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Resolving open/close, attach/detach races
The attached patch series enables us to resolve a large class of races
between devsw open/close, autoconf attach/detach, and module unload.
For example, if xyzopen does
if ((sc = device_lookup_private(&xyz_cd, minor(dev))) == NULL)
return ENXIO;
mutex_enter(&sc->sc_lock);
and if xyz_detach runs concurrently, then xyzopen may obtain a
non-null softc pointer that is immediately freed by the concurrent
xyz_detach. This problem affects essentially every driver in tree
that has devsw operations (userland /dev nodes) coupled with autoconf
device instances. There are a host of other similar problems, like
opening a device while attach is in progress, or detaching a device
that is in the middle of bdev_strategy.
Resolving the races for a driver requires opting in via bdevsw/cdevsw.
Pretty much any driver whose devsw operations that use device_lookup
should opt into this. Making a driver opt in is just a matter of
adding:
static const struct xyz_cdevsw = {
...
.d_cfdriver = &xyz_cd,
.d_devtounit = dev_minor_unit,
...
};
The .d_cfdriver member points at an autoconf cfdriver, and the
.d_devtounit member gives a function that maps a dev_t to a
nonnegative int autoconf unit. Two built-in functions --
dev_minor_unit and disklabel_dev_unit -- cover the vast majority of
existing cases where devsw and autoconf are coupled together. Same
deal for bdevsw as for cdevsw.
Once opted in, the system provides a number of new guarantees for
drivers that enable simplifications (as demonstrated at the end of the
patch series):
- xyzopen and xyz_attach never run concurrently, so device_lookup in
xyzopen never returns a device with partially initialized softc.
The thread in which xyz_attach is running is allowed to call
cdev_open(xyz) and anything else that uses device_lookup_acquire --
but _only_ that thread, until xyz_attach has completed.
- xyzopen and xyz_detach never run concurrently, so device_lookup in
xyzopen returns a stable pointer that doesn't go away until after
xyzopen returns. (If xyz_detach backs out, it unblocks any waiting
xyzopen calls.)
- Provided xyz_detach causes subsequent xyzopen to fail gracefully, if
xyz_detach calls vdevgone then it is guaranteed all devsw operations
have completed and instances have been closed. This means a lot of
driver-specific reference-counting of devsw operations can be
tossed.
- Since xyzopen and xyz_detach never run concurrently, the xyzclose in
vdevgone called from xyz_detach never runs concurrently with xyzopen
either.
I opted a handful of drivers in, and demonstrated removing unnecessary
driver-specific reference-counting mechanisms in uhid(4).
The patch also introduces two new functions: device_lookup_acquire and
device_release. device_lookup_acquire is like device_lookup, but if
attach or detach is in progress, it waits for them to complete; and if
successful, it holds a reference to the device that blocks detach
until the caller invokes device_release.
Most drivers don't have to use these: opting into the devsw/autoconf
hooks has the side effect that all calls to xyzopen are bracketed by
acquiring/releasing the device automatically. But in rare cases it
may be necessary to use device_lookup_acquire, e.g. in audiobell.
The patch also fixes issues with devsw_detach on module unload. It is
the caller's responsibility to ensure all autoconf instances are
detached _before_ calling devsw_detach on unload. devsw_detach now
returns void, not an error code, so there is no longer any need to
flail around trying to roll back detachment if devsw_detach fails
(which it never did anyway but we have oodles of dead error branches I
pruned in this patch series).
Caveats:
1. I haven't done anything with ttys yet. Not sure what additional
problems they pose -- but it is unlikely this branch will make them
worse.
2. I haven't done anything with pseudo-devices yet -- device_lookup as
used in, e.g., cgd_open may still be racy. There's a complication
because, e.g., cgd_detach _can't_ issue vdevgone, which would wait
for cgd_close because it's cgd_close that calls cgd_detach in the
first place, TBD.
3. I haven't done a lot of testing yet, just some stress-testing with
uhid(4) open/close attach/detach and umass(4) mount/tar
attach/detach. Might crash horribly in an atf test run, but I'm
reasonably confident most of the principles underlying the patch
series are sound.
Comments, reports of testing, and other input welcome!
>From 9a6ad667fa6456d238e2b5e3c74f930fa83f99c3 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Wed, 12 Jan 2022 00:46:40 +0000
Subject: [PATCH 01/13] driver(9): devsw_detach never fails. Make it return
void.
Prune a whole lotta dead branches as a result of this. (Some logic
calling this is also wrong for other reasons; devsw_detach is final
-- you should never have any reason to decide to roll it back. To be
cleaned up in subsequent commits...)
---
external/cddl/osnet/dev/dtrace/dtrace_modevent.c | 4 +---
external/cddl/osnet/dev/fbt/fbt.c | 3 ++-
external/cddl/osnet/dev/sdt/sdt.c | 3 ++-
.../cddl/osnet/dist/uts/common/fs/zfs/zfs_ioctl.c | 2 +-
share/man/man9/devsw_attach.9 | 15 +++++++++------
sys/coda/coda_psdev.c | 2 +-
sys/dev/ccd.c | 2 +-
sys/dev/clockctl.c | 8 +++-----
sys/dev/hdaudio/hdaudio.c | 6 +-----
sys/dev/i2c/i2c.c | 7 ++-----
sys/dev/pad/pad.c | 4 +---
sys/dev/raidframe/rf_netbsdkintf.c | 11 +----------
sys/dev/sysmon/sysmon.c | 2 +-
sys/dev/tprof/tprof.c | 8 +-------
sys/dist/pf/net/pf_ioctl.c | 3 ++-
sys/external/bsd/ipf/netinet/ip_fil_netbsd.c | 2 +-
sys/fs/autofs/autofs_vfsops.c | 4 +---
sys/kern/kern_drvctl.c | 9 ++-------
sys/kern/subr_devsw.c | 3 +--
sys/modules/examples/pollpal/pollpal.c | 3 ++-
sys/net/if_tap.c | 5 +----
sys/net/if_tun.c | 9 +--------
sys/rump/dev/lib/libbpf/bpf_component.c | 3 +--
sys/rump/dev/lib/libdrvctl/drvctl_component.c | 4 +---
sys/sys/conf.h | 2 +-
25 files changed, 41 insertions(+), 83 deletions(-)
diff --git a/external/cddl/osnet/dev/dtrace/dtrace_modevent.c b/external/cddl/osnet/dev/dtrace/dtrace_modevent.c
index cc0f8103fb98..f1338840125a 100644
--- a/external/cddl/osnet/dev/dtrace/dtrace_modevent.c
+++ b/external/cddl/osnet/dev/dtrace/dtrace_modevent.c
@@ -42,9 +42,7 @@ dtrace_modcmd(modcmd_t cmd, void *data)
return error;
case MODULE_CMD_FINI:
- error = devsw_detach(NULL, &dtrace_cdevsw);
- if (error != 0)
- return error;
+ devsw_detach(NULL, &dtrace_cdevsw);
error = dtrace_unload();
if (error != 0) {
diff --git a/external/cddl/osnet/dev/fbt/fbt.c b/external/cddl/osnet/dev/fbt/fbt.c
index b367c2155292..46dd7c1f7f06 100644
--- a/external/cddl/osnet/dev/fbt/fbt.c
+++ b/external/cddl/osnet/dev/fbt/fbt.c
@@ -1329,7 +1329,8 @@ dtrace_fbt_modcmd(modcmd_t cmd, void *data)
error = fbt_unload();
if (error != 0)
return error;
- return devsw_detach(NULL, &fbt_cdevsw);
+ devsw_detach(NULL, &fbt_cdevsw);
+ return 0;
case MODULE_CMD_AUTOUNLOAD:
return EBUSY;
default:
diff --git a/external/cddl/osnet/dev/sdt/sdt.c b/external/cddl/osnet/dev/sdt/sdt.c
index c3ad129f8284..5a41270a2917 100644
--- a/external/cddl/osnet/dev/sdt/sdt.c
+++ b/external/cddl/osnet/dev/sdt/sdt.c
@@ -562,7 +562,8 @@ dtrace_sdt_modcmd(modcmd_t cmd, void *data)
error = sdt_unload();
if (error != 0)
return error;
- return devsw_detach(NULL, &sdt_cdevsw);
+ devsw_detach(NULL, &sdt_cdevsw);
+ return 0;
case MODULE_CMD_AUTOUNLOAD:
return EBUSY;
default:
diff --git a/external/cddl/osnet/dist/uts/common/fs/zfs/zfs_ioctl.c b/external/cddl/osnet/dist/uts/common/fs/zfs/zfs_ioctl.c
index 9e19cd1dc0c3..d74d8c71e54d 100644
--- a/external/cddl/osnet/dist/uts/common/fs/zfs/zfs_ioctl.c
+++ b/external/cddl/osnet/dist/uts/common/fs/zfs/zfs_ioctl.c
@@ -7231,7 +7231,7 @@ zfs_modcmd(modcmd_t cmd, void *arg)
if (error)
return error;
- (void) devsw_detach(&zfs_bdevsw, &zfs_cdevsw);
+ devsw_detach(&zfs_bdevsw, &zfs_cdevsw);
attacherr:
zfs_sysctl_fini();
diff --git a/share/man/man9/devsw_attach.9 b/share/man/man9/devsw_attach.9
index cf862be5846a..6ffc51957a3f 100644
--- a/share/man/man9/devsw_attach.9
+++ b/share/man/man9/devsw_attach.9
@@ -27,7 +27,7 @@
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
-.Dd April 30, 2017
+.Dd January 11, 2022
.Dt DEVSW 9
.Os
.Sh NAME
@@ -49,7 +49,7 @@
.Fa "const struct cdevsw *cdev"
.Fa "devmajor_t *cmajor"
.Fc
-.Ft int
+.Ft void
.Fo devsw_detach
.Fa "const struct bdevsw *bdev"
.Fa "const struct cdevsw *cdev"
@@ -130,6 +130,11 @@ and
structures.
.Fn devsw_detach
should be called before a loaded device driver is unloaded.
+The caller must ensure that there are no open instances of the device,
+and that the device's
+.Fn d_open
+function will fail, before calling.
+Fn devsw_detach .
.Pp
The
.Fn bdevsw_lookup
@@ -155,10 +160,8 @@ or
.Sh RETURN VALUES
Upon successful completion,
.Fn devsw_attach
-and
-.Fn devsw_detach
-return 0.
-Otherwise they return an error value.
+returns 0.
+Otherwise it returns an error value.
.Pp
In case of failure,
.Fn bdevsw_lookup
diff --git a/sys/coda/coda_psdev.c b/sys/coda/coda_psdev.c
index cede16da3f53..7f531f03fe56 100644
--- a/sys/coda/coda_psdev.c
+++ b/sys/coda/coda_psdev.c
@@ -758,7 +758,7 @@ vcoda_modcmd(modcmd_t cmd, void *arg)
if (VC_OPEN(vcp))
return EBUSY;
}
- return devsw_detach(NULL, &vcoda_cdevsw);
+ devsw_detach(NULL, &vcoda_cdevsw);
}
#endif
break;
diff --git a/sys/dev/ccd.c b/sys/dev/ccd.c
index 05945f9a67ba..2283bc0346da 100644
--- a/sys/dev/ccd.c
+++ b/sys/dev/ccd.c
@@ -1710,7 +1710,7 @@ ccd_modcmd(modcmd_t cmd, void *arg)
error = EBUSY;
} else {
mutex_exit(&ccd_lock);
- error = devsw_detach(&ccd_bdevsw, &ccd_cdevsw);
+ devsw_detach(&ccd_bdevsw, &ccd_cdevsw);
ccddetach();
}
#endif
diff --git a/sys/dev/clockctl.c b/sys/dev/clockctl.c
index 0da5e7765fe8..9685c0f129f6 100644
--- a/sys/dev/clockctl.c
+++ b/sys/dev/clockctl.c
@@ -182,14 +182,12 @@ clockctl_modcmd(modcmd_t cmd, void *data)
return EBUSY;
}
#ifdef _MODULE
- error = devsw_detach(NULL, &clockctl_cdevsw);
+ devsw_detach(NULL, &clockctl_cdevsw);
#endif
mutex_exit(&clockctl_mtx);
- if (error == 0) {
- kauth_unlisten_scope(clockctl_listener);
- mutex_destroy(&clockctl_mtx);
- }
+ kauth_unlisten_scope(clockctl_listener);
+ mutex_destroy(&clockctl_mtx);
break;
default:
diff --git a/sys/dev/hdaudio/hdaudio.c b/sys/dev/hdaudio/hdaudio.c
index d39ff2db6cde..5c7874778e22 100644
--- a/sys/dev/hdaudio/hdaudio.c
+++ b/sys/dev/hdaudio/hdaudio.c
@@ -1636,11 +1636,7 @@ hdaudio_modcmd(modcmd_t cmd, void *opaque)
error = config_cfdriver_detach(&hdaudio_cd);
if (error)
break;
- error = devsw_detach(NULL, &hdaudio_cdevsw);
- if (error) {
- config_cfdriver_attach(&hdaudio_cd);
- break;
- }
+ devsw_detach(NULL, &hdaudio_cdevsw);
#endif
break;
default:
diff --git a/sys/dev/i2c/i2c.c b/sys/dev/i2c/i2c.c
index 322f6ad3f199..b56b3e235112 100644
--- a/sys/dev/i2c/i2c.c
+++ b/sys/dev/i2c/i2c.c
@@ -904,7 +904,7 @@ iic_modcmd(modcmd_t cmd, void *opaque)
if (error) {
aprint_error("%s: unable to init component\n",
iic_cd.cd_name);
- (void)devsw_detach(NULL, &iic_cdevsw);
+ devsw_detach(NULL, &iic_cdevsw);
}
mutex_exit(&iic_mtx);
#endif
@@ -922,10 +922,7 @@ iic_modcmd(modcmd_t cmd, void *opaque)
mutex_exit(&iic_mtx);
break;
}
- error = devsw_detach(NULL, &iic_cdevsw);
- if (error != 0)
- config_init_component(cfdriver_ioconf_iic,
- cfattach_ioconf_iic, cfdata_ioconf_iic);
+ devsw_detach(NULL, &iic_cdevsw);
#endif
mutex_exit(&iic_mtx);
break;
diff --git a/sys/dev/pad/pad.c b/sys/dev/pad/pad.c
index fe0b429cf386..a779f1f71b8d 100644
--- a/sys/dev/pad/pad.c
+++ b/sys/dev/pad/pad.c
@@ -777,9 +777,7 @@ pad_modcmd(modcmd_t cmd, void *arg)
case MODULE_CMD_FINI:
#ifdef _MODULE
- error = devsw_detach(NULL, &pad_cdevsw);
- if (error)
- break;
+ devsw_detach(NULL, &pad_cdevsw);
error = config_fini_component(cfdriver_ioconf_pad,
pad_cfattach, cfdata_ioconf_pad);
diff --git a/sys/dev/raidframe/rf_netbsdkintf.c b/sys/dev/raidframe/rf_netbsdkintf.c
index d1bda3553e03..87439aa70bfb 100644
--- a/sys/dev/raidframe/rf_netbsdkintf.c
+++ b/sys/dev/raidframe/rf_netbsdkintf.c
@@ -4088,16 +4088,7 @@ raid_modcmd_fini(void)
return error;
}
#endif
- error = devsw_detach(&raid_bdevsw, &raid_cdevsw);
- if (error != 0) {
- aprint_error("%s: cannot detach devsw\n",__func__);
-#ifdef _MODULE
- config_cfdriver_attach(&raid_cd);
-#endif
- config_cfattach_attach(raid_cd.cd_name, &raid_ca);
- mutex_exit(&raid_lock);
- return error;
- }
+ devsw_detach(&raid_bdevsw, &raid_cdevsw);
rf_BootRaidframe(false);
#if (RF_INCLUDE_PARITY_DECLUSTERING_DS > 0)
rf_destroy_mutex2(rf_sparet_wait_mutex);
diff --git a/sys/dev/sysmon/sysmon.c b/sys/dev/sysmon/sysmon.c
index 46aedaad7337..fd2993f0c180 100644
--- a/sys/dev/sysmon/sysmon.c
+++ b/sys/dev/sysmon/sysmon.c
@@ -356,7 +356,7 @@ sysmon_fini(void)
if (error == 0) {
mutex_enter(&sysmon_minor_mtx);
sm_is_attached = false;
- error = devsw_detach(NULL, &sysmon_cdevsw);
+ devsw_detach(NULL, &sysmon_cdevsw);
mutex_exit(&sysmon_minor_mtx);
}
#endif
diff --git a/sys/dev/tprof/tprof.c b/sys/dev/tprof/tprof.c
index b069a5b7df5d..136fd190ad14 100644
--- a/sys/dev/tprof/tprof.c
+++ b/sys/dev/tprof/tprof.c
@@ -768,13 +768,7 @@ tprof_modcmd(modcmd_t cmd, void *arg)
case MODULE_CMD_FINI:
#if defined(_MODULE)
- {
- int error;
- error = devsw_detach(NULL, &tprof_cdevsw);
- if (error) {
- return error;
- }
- }
+ devsw_detach(NULL, &tprof_cdevsw);
#endif /* defined(_MODULE) */
tprof_driver_fini();
return 0;
diff --git a/sys/dist/pf/net/pf_ioctl.c b/sys/dist/pf/net/pf_ioctl.c
index 94bfb70a411d..e4c13be698f8 100644
--- a/sys/dist/pf/net/pf_ioctl.c
+++ b/sys/dist/pf/net/pf_ioctl.c
@@ -3459,7 +3459,8 @@ pf_modcmd(modcmd_t cmd, void *opaque)
} else {
pfdetach();
pflogdetach();
- return devsw_detach(NULL, &pf_cdevsw);
+ devsw_detach(NULL, &pf_cdevsw);
+ return 0;
}
default:
return ENOTTY;
diff --git a/sys/external/bsd/ipf/netinet/ip_fil_netbsd.c b/sys/external/bsd/ipf/netinet/ip_fil_netbsd.c
index d0c4ca95097c..bb4e0706cc9b 100644
--- a/sys/external/bsd/ipf/netinet/ip_fil_netbsd.c
+++ b/sys/external/bsd/ipf/netinet/ip_fil_netbsd.c
@@ -2256,7 +2256,7 @@ ipl_fini(void *opaque)
{
#ifdef _MODULE
- (void)devsw_detach(NULL, &ipl_cdevsw);
+ devsw_detach(NULL, &ipl_cdevsw);
#endif
/*
diff --git a/sys/fs/autofs/autofs_vfsops.c b/sys/fs/autofs/autofs_vfsops.c
index fbd6eafe6532..1204d1f9b6d3 100644
--- a/sys/fs/autofs/autofs_vfsops.c
+++ b/sys/fs/autofs/autofs_vfsops.c
@@ -496,9 +496,7 @@ autofs_modcmd(modcmd_t cmd, void *arg)
}
mutex_exit(&autofs_softc->sc_lock);
- error = devsw_detach(NULL, &autofs_cdevsw);
- if (error)
- break;
+ devsw_detach(NULL, &autofs_cdevsw);
#endif
error = vfs_detach(&autofs_vfsops);
if (error)
diff --git a/sys/kern/kern_drvctl.c b/sys/kern/kern_drvctl.c
index 37f4730b2512..8a4156f8a0aa 100644
--- a/sys/kern/kern_drvctl.c
+++ b/sys/kern/kern_drvctl.c
@@ -665,15 +665,10 @@ drvctl_modcmd(modcmd_t cmd, void *arg)
devmon_insert_vec = saved_insert_vec;
saved_insert_vec = NULL;
#ifdef _MODULE
- error = devsw_detach(NULL, &drvctl_cdevsw);
- if (error != 0) {
- saved_insert_vec = devmon_insert_vec;
- devmon_insert_vec = devmon_insert;
- }
+ devsw_detach(NULL, &drvctl_cdevsw);
#endif
mutex_exit(&drvctl_lock);
- if (error == 0)
- drvctl_fini();
+ drvctl_fini();
break;
default:
diff --git a/sys/kern/subr_devsw.c b/sys/kern/subr_devsw.c
index 1a0f721fdd65..b95a09d3e6b6 100644
--- a/sys/kern/subr_devsw.c
+++ b/sys/kern/subr_devsw.c
@@ -343,14 +343,13 @@ devsw_detach_locked(const struct bdevsw *bdev, const struct cdevsw *cdev)
}
}
-int
+void
devsw_detach(const struct bdevsw *bdev, const struct cdevsw *cdev)
{
mutex_enter(&device_lock);
devsw_detach_locked(bdev, cdev);
mutex_exit(&device_lock);
- return 0;
}
/*
diff --git a/sys/modules/examples/pollpal/pollpal.c b/sys/modules/examples/pollpal/pollpal.c
index b76e0733699b..d8ddc73450e0 100644
--- a/sys/modules/examples/pollpal/pollpal.c
+++ b/sys/modules/examples/pollpal/pollpal.c
@@ -311,7 +311,8 @@ pollpal_modcmd(modcmd_t cmd, void *arg __unused)
case MODULE_CMD_FINI:
if (pollpal_nopen != 0)
return EBUSY;
- return devsw_detach(NULL, &pollpal_cdevsw);
+ devsw_detach(NULL, &pollpal_cdevsw);
+ return 0;
default:
return ENOTTY;
}
diff --git a/sys/net/if_tap.c b/sys/net/if_tap.c
index 0b57ad4a711c..314f4647707c 100644
--- a/sys/net/if_tap.c
+++ b/sys/net/if_tap.c
@@ -256,9 +256,7 @@ tapdetach(void)
if_clone_detach(&tap_cloners);
#ifdef _MODULE
- error = devsw_detach(NULL, &tap_cdevsw);
- if (error != 0)
- goto out2;
+ devsw_detach(NULL, &tap_cdevsw);
#endif
if (tap_count != 0) {
@@ -277,7 +275,6 @@ tapdetach(void)
out1:
#ifdef _MODULE
devsw_attach("tap", NULL, &tap_bmajor, &tap_cdevsw, &tap_cmajor);
- out2:
#endif
if_clone_attach(&tap_cloners);
diff --git a/sys/net/if_tun.c b/sys/net/if_tun.c
index 4f533a8f08d1..f4e5b6d86d43 100644
--- a/sys/net/if_tun.c
+++ b/sys/net/if_tun.c
@@ -142,17 +142,10 @@ tuninit(void)
static int
tundetach(void)
{
-#ifdef _MODULE
- int error;
-#endif
if_clone_detach(&tun_cloner);
#ifdef _MODULE
- error = devsw_detach(NULL, &tun_cdevsw);
- if (error != 0) {
- if_clone_attach(&tun_cloner);
- return error;
- }
+ devsw_detach(NULL, &tun_cdevsw);
#endif
if (!LIST_EMPTY(&tun_softc_list) || !LIST_EMPTY(&tunz_softc_list)) {
diff --git a/sys/rump/dev/lib/libbpf/bpf_component.c b/sys/rump/dev/lib/libbpf/bpf_component.c
index 05807d371d40..d41d1987afe8 100644
--- a/sys/rump/dev/lib/libbpf/bpf_component.c
+++ b/sys/rump/dev/lib/libbpf/bpf_component.c
@@ -50,6 +50,5 @@ RUMP_COMPONENT(RUMP_COMPONENT_NET)
panic("bpf devsw attach failed: %d", error);
if ((error = rump_vfs_makeonedevnode(S_IFCHR, "/dev/bpf", cmaj, 0)) !=0)
panic("cannot create bpf device nodes: %d", error);
- if ((error = devsw_detach(NULL, &bpf_cdevsw)) != 0)
- panic("cannot detach bpf devsw: %d", error);
+ devsw_detach(NULL, &bpf_cdevsw);
}
diff --git a/sys/rump/dev/lib/libdrvctl/drvctl_component.c b/sys/rump/dev/lib/libdrvctl/drvctl_component.c
index e2e79f45f9de..ac4e103fdb9c 100644
--- a/sys/rump/dev/lib/libdrvctl/drvctl_component.c
+++ b/sys/rump/dev/lib/libdrvctl/drvctl_component.c
@@ -51,7 +51,5 @@ RUMP_COMPONENT(RUMP_COMPONENT_DEV)
if ( error !=0)
panic("cannot create drvctl device node: %d", error);
- error = devsw_detach(NULL, &drvctl_cdevsw);
- if (error != 0)
- panic("cannot detach drvctl devsw: %d", error);
+ devsw_detach(NULL, &drvctl_cdevsw);
}
diff --git a/sys/sys/conf.h b/sys/sys/conf.h
index 081631d2111f..ba46976a924b 100644
--- a/sys/sys/conf.h
+++ b/sys/sys/conf.h
@@ -104,7 +104,7 @@ extern kmutex_t device_lock;
int devsw_attach(const char *, const struct bdevsw *, devmajor_t *,
const struct cdevsw *, devmajor_t *);
-int devsw_detach(const struct bdevsw *, const struct cdevsw *);
+void devsw_detach(const struct bdevsw *, const struct cdevsw *);
const struct bdevsw *bdevsw_lookup(dev_t);
const struct cdevsw *cdevsw_lookup(dev_t);
devmajor_t bdevsw_lookup_major(const struct bdevsw *);
>From 0774d5ff5a0dac90f9fb53b03dab728b05fb6ee2 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Wed, 12 Jan 2022 01:05:24 +0000
Subject: [PATCH 02/13] driver(9): Fix synchronization of
devsw_attach/lookup/detach.
(`dev' means either `bdev' or `cdev' for brevity here, e.g. in
`devsw_lookup' (bdevsw_lookup, cdevsw_lookup), `dev_open' (bdev_open,
cdev_open), `maxdevsws', &c., except for `devsw_attach' and
`devsw_detach' which are taken literally.)
- Use atomic_store_release and atomic_load_consume for devsw and
tables and their entries, which are read unlocked and thus require
memory barriers to ensure ordering between initialization in
devsw_attach and use in dev_lookup.
- Use pserialize(9) and localcount(9) to synchronize dev_open and
devsw_detach.
=> Driver must ensure d_open fails and all open instances have been
closed by the time it calls devsw_detach.
=> Bonus: dev_open is no longer globally serialized through
device_lock.
- Use atomic_store_release and atomic_load_acquire for max_devsws,
which is used in conditionals in the new devsw_lookup_acquire.
=> It is safe to use atomic_load_relaxed in devsw_lookup because
the caller must guarantee the entry is stable, so any increase
of max_devsws must have already happened.
=> devsw_lookup and devsw_lookup_acquire assume that max_devsws
never goes down. If you change this you must find some way to
adapt the users, preferably without adding much overhead so that
devsw operations are cheap.
This change introduces an auxiliary table devswref mapping device
majors to localcounts of opens in progress. The auxiliary table only
occupies one pointer's worth of memory in a monolithic kernel, and is
allocated on the fly for dynamically loaded modules. We could ask
the module itself to reserve storage for it, but I don't see much
value in that, and it would require some changes to the ABI and to
config(8).
---
sys/kern/subr_devsw.c | 285 +++++++++++++++++++++++++++++++++++-------
1 file changed, 238 insertions(+), 47 deletions(-)
diff --git a/sys/kern/subr_devsw.c b/sys/kern/subr_devsw.c
index b95a09d3e6b6..1145bf83a08c 100644
--- a/sys/kern/subr_devsw.c
+++ b/sys/kern/subr_devsw.c
@@ -85,6 +85,9 @@ __KERNEL_RCSID(0, "$NetBSD: subr_devsw.c,v 1.38 2017/11/07 18:35:57 christos Exp
#include <sys/buf.h>
#include <sys/reboot.h>
#include <sys/sdt.h>
+#include <sys/atomic.h>
+#include <sys/localcount.h>
+#include <sys/pserialize.h>
#ifdef DEVSW_DEBUG
#define DPRINTF(x) printf x
@@ -97,12 +100,22 @@ __KERNEL_RCSID(0, "$NetBSD: subr_devsw.c,v 1.38 2017/11/07 18:35:57 christos Exp
#define CDEVSW_SIZE (sizeof(struct cdevsw *))
#define DEVSWCONV_SIZE (sizeof(struct devsw_conv))
+struct devswref {
+ struct localcount dr_lc;
+};
+
+/* XXX bdevsw, cdevsw, max_bdevsws, and max_cdevsws should be volatile */
extern const struct bdevsw **bdevsw, *bdevsw0[];
extern const struct cdevsw **cdevsw, *cdevsw0[];
extern struct devsw_conv *devsw_conv, devsw_conv0[];
extern const int sys_bdevsws, sys_cdevsws;
extern int max_bdevsws, max_cdevsws, max_devsw_convs;
+static struct devswref *cdevswref;
+static struct devswref *bdevswref;
+static struct pserialize *devsw_psz;
+static kcondvar_t devsw_cv;
+
static int bdevsw_attach(const struct bdevsw *, devmajor_t *);
static int cdevsw_attach(const struct cdevsw *, devmajor_t *);
static void devsw_detach_locked(const struct bdevsw *, const struct cdevsw *);
@@ -118,6 +131,9 @@ devsw_init(void)
KASSERT(sys_bdevsws < MAXDEVSW - 1);
KASSERT(sys_cdevsws < MAXDEVSW - 1);
mutex_init(&device_lock, MUTEX_DEFAULT, IPL_NONE);
+
+ devsw_psz = pserialize_create();
+ cv_init(&devsw_cv, "devsw");
}
int
@@ -160,13 +176,17 @@ devsw_attach(const char *devname,
}
if (bdev != NULL)
- bdevsw[*bmajor] = bdev;
- cdevsw[*cmajor] = cdev;
+ atomic_store_release(&bdevsw[*bmajor], bdev);
+ atomic_store_release(&cdevsw[*cmajor], cdev);
mutex_exit(&device_lock);
return (0);
}
+ /*
+ * XXX This should allocate what it needs up front so we never
+ * need to flail around trying to unwind.
+ */
error = bdevsw_attach(bdev, bmajor);
if (error != 0)
goto fail;
@@ -224,7 +244,8 @@ devsw_attach(const char *devname,
static int
bdevsw_attach(const struct bdevsw *devsw, devmajor_t *devmajor)
{
- const struct bdevsw **newptr;
+ const struct bdevsw **newbdevsw = NULL;
+ struct devswref *newbdevswref = NULL;
devmajor_t bmajor;
int i;
@@ -255,18 +276,34 @@ bdevsw_attach(const struct bdevsw *devsw, devmajor_t *devmajor)
if (*devmajor >= max_bdevsws) {
KASSERT(bdevsw == bdevsw0);
- newptr = kmem_zalloc(MAXDEVSW * BDEVSW_SIZE, KM_NOSLEEP);
- if (newptr == NULL)
+ newbdevsw = kmem_zalloc(MAXDEVSW * sizeof(newbdevsw[0]),
+ KM_NOSLEEP);
+ newbdevswref = kmem_zalloc(((MAXDEVSW - sys_bdevsws) *
+ sizeof(newbdevsw[0])),
+ KM_NOSLEEP);
+ if (newbdevsw == NULL || newbdevswref == NULL) {
+ if (newbdevsw) {
+ kmem_free(newbdevsw,
+ MAXDEVSW * sizeof(newbdevsw[0]));
+ }
+ if (newbdevswref) {
+ kmem_free(newbdevswref,
+ ((MAXDEVSW - sys_bdevsws) *
+ sizeof(newbdevswref[0])));
+ }
return (ENOMEM);
- memcpy(newptr, bdevsw, max_bdevsws * BDEVSW_SIZE);
- bdevsw = newptr;
- max_bdevsws = MAXDEVSW;
+ }
+ memcpy(newbdevsw, bdevsw, max_bdevsws * BDEVSW_SIZE);
+ atomic_store_release(&bdevsw, newbdevsw);
+ atomic_store_release(&bdevswref, newbdevswref);
+ atomic_store_release(&max_bdevsws, MAXDEVSW);
}
if (bdevsw[*devmajor] != NULL)
return (EEXIST);
- bdevsw[*devmajor] = devsw;
+ atomic_store_release(&bdevsw[*devmajor], devsw);
+ localcount_init(&bdevswref[*devmajor - sys_bdevsws].dr_lc);
return (0);
}
@@ -274,7 +311,8 @@ bdevsw_attach(const struct bdevsw *devsw, devmajor_t *devmajor)
static int
cdevsw_attach(const struct cdevsw *devsw, devmajor_t *devmajor)
{
- const struct cdevsw **newptr;
+ const struct cdevsw **newcdevsw = NULL;
+ struct devswref *newcdevswref = NULL;
devmajor_t cmajor;
int i;
@@ -302,18 +340,34 @@ cdevsw_attach(const struct cdevsw *devsw, devmajor_t *devmajor)
if (*devmajor >= max_cdevsws) {
KASSERT(cdevsw == cdevsw0);
- newptr = kmem_zalloc(MAXDEVSW * CDEVSW_SIZE, KM_NOSLEEP);
- if (newptr == NULL)
+ newcdevsw = kmem_zalloc(MAXDEVSW * sizeof(newcdevsw[0]),
+ KM_NOSLEEP);
+ newcdevswref = kmem_zalloc(((MAXDEVSW - sys_cdevsws) *
+ sizeof(newcdevswref[0])),
+ KM_NOSLEEP);
+ if (newcdevsw == NULL || newcdevswref == NULL) {
+ if (newcdevsw) {
+ kmem_free(newcdevsw,
+ MAXDEVSW * sizeof(newcdevsw[0]));
+ }
+ if (newcdevswref) {
+ kmem_free(newcdevswref,
+ ((MAXDEVSW - sys_cdevsws) *
+ sizeof(newcdevswref[0])));
+ }
return (ENOMEM);
- memcpy(newptr, cdevsw, max_cdevsws * CDEVSW_SIZE);
- cdevsw = newptr;
- max_cdevsws = MAXDEVSW;
+ }
+ memcpy(newcdevsw, cdevsw, max_cdevsws * sizeof(cdevsw[0]));
+ atomic_store_release(&cdevsw, newcdevsw);
+ atomic_store_release(&cdevswref, newcdevswref);
+ atomic_store_release(&max_cdevsws, MAXDEVSW);
}
if (cdevsw[*devmajor] != NULL)
return (EEXIST);
- cdevsw[*devmajor] = devsw;
+ atomic_store_release(&cdevsw[*devmajor], devsw);
+ localcount_init(&cdevswref[*devmajor - sys_cdevsws].dr_lc);
return (0);
}
@@ -321,25 +375,56 @@ cdevsw_attach(const struct cdevsw *devsw, devmajor_t *devmajor)
static void
devsw_detach_locked(const struct bdevsw *bdev, const struct cdevsw *cdev)
{
- int i;
+ int bi, ci;
KASSERT(mutex_owned(&device_lock));
+ /* Prevent new references. */
if (bdev != NULL) {
- for (i = 0 ; i < max_bdevsws ; i++) {
- if (bdevsw[i] != bdev)
+ for (bi = 0; bi < max_bdevsws; bi++) {
+ if (bdevsw[bi] != bdev)
continue;
- bdevsw[i] = NULL;
+ atomic_store_relaxed(&bdevsw[bi], NULL);
break;
}
+ KASSERT(bi < max_bdevsws);
}
if (cdev != NULL) {
- for (i = 0 ; i < max_cdevsws ; i++) {
- if (cdevsw[i] != cdev)
+ for (ci = 0; ci < max_cdevsws; ci++) {
+ if (cdevsw[ci] != cdev)
continue;
- cdevsw[i] = NULL;
+ atomic_store_relaxed(&cdevsw[ci], NULL);
break;
}
+ KASSERT(ci < max_cdevsws);
+ }
+
+ if (bdev == NULL && cdev == NULL) /* XXX possible? */
+ return;
+
+ /*
+ * Wait for all bdevsw_lookup_acquire, cdevsw_lookup_acquire
+ * calls to notice that the devsw is gone.
+ */
+ pserialize_perform(devsw_psz);
+
+ /*
+ * Wait for all references to drain. It is the caller's
+ * responsibility to ensure that at this point, there are no
+ * extant open instances and all new d_open calls will fail.
+ *
+ * Note that localcount_drain may release and reacquire
+ * device_lock.
+ */
+ if (bdev != NULL) {
+ localcount_drain(&bdevswref[bi - sys_bdevsws].dr_lc,
+ &devsw_cv, &device_lock);
+ localcount_fini(&bdevswref[bi - sys_bdevsws].dr_lc);
+ }
+ if (cdev != NULL) {
+ localcount_drain(&cdevswref[ci - sys_cdevsws].dr_lc,
+ &devsw_cv, &device_lock);
+ localcount_fini(&cdevswref[ci - sys_cdevsws].dr_lc);
}
}
@@ -365,10 +450,63 @@ bdevsw_lookup(dev_t dev)
if (dev == NODEV)
return (NULL);
bmajor = major(dev);
- if (bmajor < 0 || bmajor >= max_bdevsws)
+ if (bmajor < 0 || bmajor >= atomic_load_relaxed(&max_bdevsws))
return (NULL);
- return (bdevsw[bmajor]);
+ return atomic_load_consume(&bdevsw)[bmajor];
+}
+
+static const struct bdevsw *
+bdevsw_lookup_acquire(dev_t dev, struct localcount **lcp)
+{
+ devmajor_t bmajor;
+ const struct bdevsw *bdev = NULL, *const *curbdevsw;
+ struct devswref *curbdevswref;
+ int s;
+
+ if (dev == NODEV)
+ return NULL;
+ bmajor = major(dev);
+ if (bmajor < 0)
+ return NULL;
+
+ /*
+ * If it's statically linked into the kernel, no need for
+ * localcount reference -- it will never go away until the
+ * machine reboots.
+ */
+ if (bmajor < sys_bdevsws) {
+ *lcp = NULL;
+ return bdevsw0[bmajor];
+ }
+
+ s = pserialize_read_enter();
+
+ /*
+ * max_bdevsws never goes down, so it is safe to rely on this
+ * condition without any locking for the array access below.
+ */
+ if (bmajor >= atomic_load_acquire(&max_bdevsws))
+ goto out;
+ curbdevsw = atomic_load_consume(&bdevsw);
+ if ((bdev = atomic_load_consume(&curbdevsw[bmajor])) == NULL)
+ goto out;
+
+ curbdevswref = atomic_load_consume(&bdevswref);
+ *lcp = &curbdevswref[bmajor - sys_bdevsws].dr_lc;
+ localcount_acquire(*lcp);
+
+out: pserialize_read_exit(s);
+ return bdev;
+}
+
+static void
+bdevsw_release(const struct bdevsw *bdev, struct localcount *lc)
+{
+
+ if (lc == NULL)
+ return;
+ localcount_release(lc, &devsw_cv, &device_lock);
}
/*
@@ -384,10 +522,63 @@ cdevsw_lookup(dev_t dev)
if (dev == NODEV)
return (NULL);
cmajor = major(dev);
- if (cmajor < 0 || cmajor >= max_cdevsws)
+ if (cmajor < 0 || cmajor >= atomic_load_relaxed(&max_cdevsws))
return (NULL);
- return (cdevsw[cmajor]);
+ return atomic_load_consume(&cdevsw)[cmajor];
+}
+
+static const struct cdevsw *
+cdevsw_lookup_acquire(dev_t dev, struct localcount **lcp)
+{
+ devmajor_t cmajor;
+ const struct cdevsw *cdev = NULL, *const *curcdevsw;
+ struct devswref *curcdevswref;
+ int s;
+
+ if (dev == NODEV)
+ return NULL;
+ cmajor = major(dev);
+ if (cmajor < 0)
+ return NULL;
+
+ /*
+ * If it's statically linked into the kernel, no need for
+ * localcount reference -- it will never go away until the
+ * machine reboots.
+ */
+ if (cmajor < sys_cdevsws) {
+ *lcp = NULL;
+ return cdevsw0[cmajor];
+ }
+
+ s = pserialize_read_enter();
+
+ /*
+ * max_cdevsws never goes down, so it is safe to rely on this
+ * condition without any locking for the array access below.
+ */
+ if (cmajor >= atomic_load_acquire(&max_cdevsws))
+ goto out;
+ curcdevsw = atomic_load_consume(&cdevsw);
+ if ((cdev = atomic_load_consume(&curcdevsw[cmajor])) == NULL)
+ goto out;
+
+ curcdevswref = atomic_load_consume(&cdevswref);
+ *lcp = &curcdevswref[cmajor - sys_cdevsws].dr_lc;
+ localcount_acquire(*lcp);
+
+out: pserialize_read_exit(s);
+ return cdev;
+}
+
+static void
+cdevsw_release(const struct cdevsw *cdev, struct localcount *lc)
+{
+
+ if (lc == NULL)
+ return;
+ localcount_release(lc, &devsw_cv, &device_lock);
}
/*
@@ -399,10 +590,13 @@ cdevsw_lookup(dev_t dev)
devmajor_t
bdevsw_lookup_major(const struct bdevsw *bdev)
{
- devmajor_t bmajor;
+ const struct bdevsw *const *curbdevsw;
+ devmajor_t bmajor, bmax;
- for (bmajor = 0 ; bmajor < max_bdevsws ; bmajor++) {
- if (bdevsw[bmajor] == bdev)
+ bmax = atomic_load_acquire(&max_bdevsws);
+ curbdevsw = atomic_load_consume(&bdevsw);
+ for (bmajor = 0; bmajor < bmax; bmajor++) {
+ if (atomic_load_relaxed(&curbdevsw[bmajor]) == bdev)
return (bmajor);
}
@@ -418,10 +612,13 @@ bdevsw_lookup_major(const struct bdevsw *bdev)
devmajor_t
cdevsw_lookup_major(const struct cdevsw *cdev)
{
- devmajor_t cmajor;
+ const struct cdevsw *const *curcdevsw;
+ devmajor_t cmajor, cmax;
- for (cmajor = 0 ; cmajor < max_cdevsws ; cmajor++) {
- if (cdevsw[cmajor] == cdev)
+ cmax = atomic_load_acquire(&max_cdevsws);
+ curcdevsw = atomic_load_consume(&cdevsw);
+ for (cmajor = 0; cmajor < cmax; cmajor++) {
+ if (atomic_load_relaxed(&curcdevsw[cmajor]) == cdev)
return (cmajor);
}
@@ -696,15 +893,10 @@ int
bdev_open(dev_t dev, int flag, int devtype, lwp_t *l)
{
const struct bdevsw *d;
+ struct localcount *lc;
int rv, mpflag;
- /*
- * For open we need to lock, in order to synchronize
- * with attach/detach.
- */
- mutex_enter(&device_lock);
- d = bdevsw_lookup(dev);
- mutex_exit(&device_lock);
+ d = bdevsw_lookup_acquire(dev, &lc);
if (d == NULL)
return ENXIO;
@@ -712,6 +904,8 @@ bdev_open(dev_t dev, int flag, int devtype, lwp_t *l)
rv = (*d->d_open)(dev, flag, devtype, l);
DEV_UNLOCK(d);
+ bdevsw_release(d, lc);
+
return rv;
}
@@ -854,15 +1048,10 @@ int
cdev_open(dev_t dev, int flag, int devtype, lwp_t *l)
{
const struct cdevsw *d;
+ struct localcount *lc;
int rv, mpflag;
- /*
- * For open we need to lock, in order to synchronize
- * with attach/detach.
- */
- mutex_enter(&device_lock);
- d = cdevsw_lookup(dev);
- mutex_exit(&device_lock);
+ d = cdevsw_lookup_acquire(dev, &lc);
if (d == NULL)
return ENXIO;
@@ -870,6 +1059,8 @@ cdev_open(dev_t dev, int flag, int devtype, lwp_t *l)
rv = (*d->d_open)(dev, flag, devtype, l);
DEV_UNLOCK(d);
+ cdevsw_release(d, lc);
+
return rv;
}
>From 265f125581de1f28fdbcc8adf700b8add6464349 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Sat, 15 Jan 2022 20:01:53 +0000
Subject: [PATCH 03/13] driver(9): Use xcall(9) rather than pserialize(9) for
devsw detach.
devsw_init is called too early for the kmem(9) in pserialize_create,
but pserialize_create doesn't do anything useful anyway.
---
sys/kern/subr_devsw.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/sys/kern/subr_devsw.c b/sys/kern/subr_devsw.c
index 1145bf83a08c..4b184e0249fc 100644
--- a/sys/kern/subr_devsw.c
+++ b/sys/kern/subr_devsw.c
@@ -88,6 +88,7 @@ __KERNEL_RCSID(0, "$NetBSD: subr_devsw.c,v 1.38 2017/11/07 18:35:57 christos Exp
#include <sys/atomic.h>
#include <sys/localcount.h>
#include <sys/pserialize.h>
+#include <sys/xcall.h>
#ifdef DEVSW_DEBUG
#define DPRINTF(x) printf x
@@ -113,7 +114,6 @@ extern int max_bdevsws, max_cdevsws, max_devsw_convs;
static struct devswref *cdevswref;
static struct devswref *bdevswref;
-static struct pserialize *devsw_psz;
static kcondvar_t devsw_cv;
static int bdevsw_attach(const struct bdevsw *, devmajor_t *);
@@ -132,7 +132,6 @@ devsw_init(void)
KASSERT(sys_cdevsws < MAXDEVSW - 1);
mutex_init(&device_lock, MUTEX_DEFAULT, IPL_NONE);
- devsw_psz = pserialize_create();
cv_init(&devsw_cv, "devsw");
}
@@ -405,8 +404,11 @@ devsw_detach_locked(const struct bdevsw *bdev, const struct cdevsw *cdev)
/*
* Wait for all bdevsw_lookup_acquire, cdevsw_lookup_acquire
* calls to notice that the devsw is gone.
+ *
+ * XXX Can't use pserialize_perform here because devsw_init is
+ * too early for pserialize_create().
*/
- pserialize_perform(devsw_psz);
+ xc_barrier(0);
/*
* Wait for all references to drain. It is the caller's
>From 9dddcf56770b483d763ac76d56c337418dec84e0 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Wed, 12 Jan 2022 14:07:35 +0000
Subject: [PATCH 04/13] autoconf(9): New localcount-based device instance
references.
device_lookup_acquire looks up an autoconf device instance, if found,
and acquires a reference the caller must release with device_release.
If attach or detach is in progress, device_lookup_acquire waits until
it completes; while references are held, detach is blocked.
The reference is meant to be held across opening a device in the
short term, and then to be passed off to a longer-term reference that
can be broken explicitly by detach -- usually a device special vnode,
which is broken by vdevgone in the driver's detach function *_detach.
Sleeping while holding a reference is allowed, but the caller
shouldn't sleep on anything that is only cancelled by *_detach,
because *_detach doesn't run until the reference is released.
The purpose of device_lookup_acquire is to let *_detach reliably
determine whether there are any open instances of the device before
it commits to detaching, without needing the kernel lock. Subsequent
changes to subr_devsw.c will make bdev_open and cdev_open take a
reference to an autoconf instance automatically so there are no logic
changes needed in the *_open devsw functions.
---
sys/kern/subr_autoconf.c | 180 ++++++++++++++++++++++++++++++++++++---
sys/sys/device.h | 6 ++
2 files changed, 174 insertions(+), 12 deletions(-)
diff --git a/sys/kern/subr_autoconf.c b/sys/kern/subr_autoconf.c
index 54391c6baea6..d98050ba7afb 100644
--- a/sys/kern/subr_autoconf.c
+++ b/sys/kern/subr_autoconf.c
@@ -108,6 +108,7 @@ __KERNEL_RCSID(0, "$NetBSD: subr_autoconf.c,v 1.291 2021/12/31 14:19:57 riastrad
#include <sys/cpu.h>
#include <sys/sysctl.h>
#include <sys/stdarg.h>
+#include <sys/localcount.h>
#include <sys/disk.h>
@@ -1453,6 +1454,9 @@ config_devdelete(device_t dev)
if (dg->dg_devs != NULL)
kmem_free(dg->dg_devs, sizeof(device_t) * dg->dg_ndevs);
+ localcount_fini(dev->dv_localcount);
+ kmem_free(dev->dv_localcount, sizeof(*dev->dv_localcount));
+
cv_destroy(&dvl->dvl_cv);
mutex_destroy(&dvl->dvl_mtx);
@@ -1556,6 +1560,7 @@ config_devalloc(const device_t parent, const cfdata_t cf,
dev->dv_activity_handlers = NULL;
dev->dv_private = dev_private;
dev->dv_flags = ca->ca_flags; /* inherit flags from class */
+ dev->dv_attaching = curlwp;
myunit = config_unit_alloc(dev, cd, cf);
if (myunit == -1) {
@@ -1604,6 +1609,10 @@ config_devalloc(const device_t parent, const cfdata_t cf,
"device-parent", device_xname(parent));
}
+ dev->dv_localcount = kmem_zalloc(sizeof(*dev->dv_localcount),
+ KM_SLEEP);
+ localcount_init(dev->dv_localcount);
+
if (dev->dv_cfdriver->cd_attrs != NULL)
config_add_attrib_dict(dev);
@@ -1755,8 +1764,29 @@ config_attach_internal(device_t parent, cfdata_t cf, void *aux, cfprint_t print,
/* Let userland know */
devmon_report_device(dev, true);
+ /*
+ * Prevent detach until the driver's attach function, and all
+ * deferred actions, have finished.
+ */
config_pending_incr(dev);
+
+ /* Call the driver's attach function. */
(*dev->dv_cfattach->ca_attach)(parent, dev, aux);
+
+ /*
+ * Allow other threads to acquire references to the device now
+ * that the driver's attach function is done.
+ */
+ mutex_enter(&config_misc_lock);
+ KASSERT(dev->dv_attaching == curlwp);
+ dev->dv_attaching = NULL;
+ cv_broadcast(&config_misc_cv);
+ mutex_exit(&config_misc_lock);
+
+ /*
+ * Synchronous parts of attach are done. Allow detach, unless
+ * the driver's attach function scheduled deferred actions.
+ */
config_pending_decr(dev);
mutex_enter(&config_misc_lock);
@@ -1822,8 +1852,29 @@ config_attach_pseudo(cfdata_t cf)
/* Let userland know */
devmon_report_device(dev, true);
+ /*
+ * Prevent detach until the driver's attach function, and all
+ * deferred actions, have finished.
+ */
config_pending_incr(dev);
+
+ /* Call the driver's attach function. */
(*dev->dv_cfattach->ca_attach)(ROOT, dev, NULL);
+
+ /*
+ * Allow other threads to acquire references to the device now
+ * that the driver's attach function is done.
+ */
+ mutex_enter(&config_misc_lock);
+ KASSERT(dev->dv_attaching == curlwp);
+ dev->dv_attaching = NULL;
+ cv_broadcast(&config_misc_cv);
+ mutex_exit(&config_misc_lock);
+
+ /*
+ * Synchronous parts of attach are done. Allow detach, unless
+ * the driver's attach function scheduled deferred actions.
+ */
config_pending_decr(dev);
config_process_deferred(&deferred_config_queue, dev);
@@ -1872,24 +1923,49 @@ config_dump_garbage(struct devicelist *garbage)
static int
config_detach_enter(device_t dev)
{
- int error;
+ int error = 0;
mutex_enter(&config_misc_lock);
- for (;;) {
- if (dev->dv_pending == 0 && dev->dv_detaching == NULL) {
- dev->dv_detaching = curlwp;
- error = 0;
- break;
- }
+
+ /*
+ * Wait until attach has fully completed, and until any
+ * concurrent detach (e.g., drvctl racing with USB event
+ * thread) has completed.
+ *
+ * Caller must hold alldevs_nread or alldevs_nwrite (e.g., via
+ * deviter) to ensure the winner of the race doesn't free the
+ * device leading the loser of the race into use-after-free.
+ *
+ * XXX Not all callers do this!
+ */
+ while (dev->dv_pending || dev->dv_detaching) {
KASSERTMSG(dev->dv_detaching != curlwp,
"recursively detaching %s", device_xname(dev));
error = cv_wait_sig(&config_misc_cv, &config_misc_lock);
if (error)
- break;
+ goto out;
}
- KASSERT(error || dev->dv_detaching == curlwp);
- mutex_exit(&config_misc_lock);
+ /*
+ * Attach has completed, and no other concurrent detach is
+ * running. Claim the device for detaching. This will cause
+ * all new attempts to acquire references to block.
+ */
+ KASSERT(dev->dv_attaching == NULL);
+ KASSERT(dev->dv_detaching == NULL);
+ dev->dv_detaching = curlwp;
+
+ /*
+ * Wait for all device_lookup_acquire references -- mostly, for
+ * all attempts to open the device -- to drain. There may
+ * still be open instances of the device after this point, but
+ * all new attempts to acquire references will block until
+ * dv_detaching clears.
+ */
+ localcount_drain(dev->dv_localcount,
+ &config_misc_cv, &config_misc_lock);
+
+out: mutex_exit(&config_misc_lock);
return error;
}
@@ -1980,9 +2056,18 @@ config_detach(device_t dev, int flags)
*/
if (rv == 0)
dev->dv_flags &= ~DVF_ACTIVE;
- else if ((flags & DETACH_FORCE) == 0)
+ else if ((flags & DETACH_FORCE) == 0) {
+ /*
+ * Detach failed -- likely EBUSY. Reset the
+ * localcount. At this point there can be no
+ * references held, and no new references acquired --
+ * calls to device_lookup_acquire are held up on
+ * dv_detaching until config_detach_exit.
+ */
+ localcount_fini(dev->dv_localcount);
+ localcount_init(dev->dv_localcount);
goto out;
- else {
+ } else {
panic("config_detach: forced detach of %s failed (%d)",
device_xname(dev), rv);
}
@@ -2498,6 +2583,14 @@ config_alldevs_exit(struct alldevs_foray *af)
* device_lookup:
*
* Look up a device instance for a given driver.
+ *
+ * Caller is responsible for ensuring the device's state is
+ * stable, either by holding a reference already obtained with
+ * device_lookup_acquire or by otherwise ensuring the device is
+ * attached and can't be detached (e.g., holding an open device
+ * node and ensuring *_detach calls vdevgone).
+ *
+ * XXX Find a way to assert this.
*/
device_t
device_lookup(cfdriver_t cd, int unit)
@@ -2526,6 +2619,69 @@ device_lookup_private(cfdriver_t cd, int unit)
return device_private(device_lookup(cd, unit));
}
+/*
+ * device_lookup_acquire:
+ *
+ * Look up a device instance for a given driver, and return a
+ * reference to it that must be released by device_release.
+ *
+ * => If the device is still attaching, blocks until *_attach has
+ * returned.
+ *
+ * => If the device is detaching, blocks until *_detach has
+ * returned. May succeed or fail in that case, depending on
+ * whether *_detach has backed out (EBUSY) or committed to
+ * detaching.
+ */
+device_t
+device_lookup_acquire(cfdriver_t cd, int unit)
+{
+ device_t dv;
+
+ /* XXX This should have a pserialized fast path -- TBD. */
+ mutex_enter(&config_misc_lock);
+ mutex_enter(&alldevs_lock);
+retry: if (unit < 0 || unit >= cd->cd_ndevs ||
+ (dv = cd->cd_devs[unit]) == NULL ||
+ dv->dv_del_gen != 0) {
+ dv = NULL;
+ } else {
+ /*
+ * Wait for the device to stabilize, if attaching or
+ * detaching. Either way we must wait for *_attach or
+ * *_detach to complete, and either way we must retry:
+ * even if detaching, *_detach might fail (EBUSY) so
+ * the device may still be there.
+ */
+ if ((dv->dv_attaching != NULL && dv->dv_attaching != curlwp) ||
+ dv->dv_detaching != NULL) {
+ mutex_exit(&alldevs_lock);
+ cv_wait(&config_misc_cv, &config_misc_lock);
+ mutex_enter(&alldevs_lock);
+ goto retry;
+ }
+ localcount_acquire(dv->dv_localcount);
+ }
+ mutex_exit(&alldevs_lock);
+ mutex_exit(&config_misc_lock);
+
+ return dv;
+}
+
+/*
+ * device_release:
+ *
+ * Release a reference to a device acquired with
+ * device_lookup_acquire.
+ */
+void
+device_release(device_t dv)
+{
+
+ localcount_release(dv->dv_localcount,
+ &config_misc_cv, &config_misc_lock);
+}
+
/*
* device_find_by_xname:
*
diff --git a/sys/sys/device.h b/sys/sys/device.h
index 99940ab1563e..76d9f8be5ad6 100644
--- a/sys/sys/device.h
+++ b/sys/sys/device.h
@@ -274,10 +274,12 @@ struct device {
void *dv_private; /* this device's private storage */
int *dv_locators; /* our actual locators (optional) */
prop_dictionary_t dv_properties;/* properties dictionary */
+ struct localcount *dv_localcount;/* reference count */
int dv_pending; /* config_pending count */
TAILQ_ENTRY(device) dv_pending_list;
+ struct lwp *dv_attaching; /* thread not yet finished in attach */
struct lwp *dv_detaching; /* detach lock (config_misc_lock/cv) */
size_t dv_activity_count;
@@ -651,6 +653,10 @@ void null_childdetached(device_t, device_t);
device_t device_lookup(cfdriver_t, int);
void *device_lookup_private(cfdriver_t, int);
+
+device_t device_lookup_acquire(cfdriver_t, int);
+void device_release(device_t);
+
void device_register(device_t, void *);
void device_register_post_config(device_t, void *);
>From 2ec3a9590a64fb19d09c3768947787cad11b73f9 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Wed, 12 Jan 2022 14:18:57 +0000
Subject: [PATCH 05/13] driver(9): New devsw members d_cfdriver, d_devtounit.
If set, then bdev_open/cdev_open will use d_devtounit to map the
dev_t to an autoconf instance (e.g., /dev/wd0a -> wd0) and hold a
reference with device_lookup_acquire across the call to d_open.
This guarantees that the autoconf instance cannot be detached while
the devsw's d_open function is trying to open it (and also that the
autoconf instance has finished *_attach before anyone can open it).
Of course, if the underlying hardware has gone away, there will be
I/O errors, but this avoids software synchronization bugs between
open and detach for drivers that opt into it. It's up to the driver
and bus to figure out how to deal with I/O errors from operations on
hardware that has gone away while the software hasn't finished
notifying everything that it's gone yet.
---
sys/kern/subr_devsw.c | 49 +++++++++++++++++++++++++++++++++++++++++--
sys/sys/conf.h | 4 ++++
2 files changed, 51 insertions(+), 2 deletions(-)
diff --git a/sys/kern/subr_devsw.c b/sys/kern/subr_devsw.c
index 4b184e0249fc..3bb9ed9daeeb 100644
--- a/sys/kern/subr_devsw.c
+++ b/sys/kern/subr_devsw.c
@@ -89,6 +89,7 @@ __KERNEL_RCSID(0, "$NetBSD: subr_devsw.c,v 1.38 2017/11/07 18:35:57 christos Exp
#include <sys/localcount.h>
#include <sys/pserialize.h>
#include <sys/xcall.h>
+#include <sys/device.h>
#ifdef DEVSW_DEBUG
#define DPRINTF(x) printf x
@@ -896,16 +897,38 @@ bdev_open(dev_t dev, int flag, int devtype, lwp_t *l)
{
const struct bdevsw *d;
struct localcount *lc;
- int rv, mpflag;
+ device_t dv = NULL/*XXXGCC*/;
+ int unit, rv, mpflag;
d = bdevsw_lookup_acquire(dev, &lc);
if (d == NULL)
return ENXIO;
+ if (d->d_devtounit) {
+ /*
+ * If the device node corresponds to an autoconf device
+ * instance, acquire a reference to it so that during
+ * d_open, device_lookup is stable.
+ *
+ * XXX This should also arrange to instantiate cloning
+ * pseudo-devices if appropriate, but that requires
+ * reviewing them all to find and verify a common
+ * pattern.
+ */
+ if ((unit = (*d->d_devtounit)(dev)) == -1)
+ return ENXIO;
+ if ((dv = device_lookup_acquire(d->d_cfdriver, unit)) == NULL)
+ return ENXIO;
+ }
+
DEV_LOCK(d);
rv = (*d->d_open)(dev, flag, devtype, l);
DEV_UNLOCK(d);
+ if (d->d_devtounit) {
+ device_release(dv);
+ }
+
bdevsw_release(d, lc);
return rv;
@@ -1051,16 +1074,38 @@ cdev_open(dev_t dev, int flag, int devtype, lwp_t *l)
{
const struct cdevsw *d;
struct localcount *lc;
- int rv, mpflag;
+ device_t dv = NULL/*XXXGCC*/;
+ int unit, rv, mpflag;
d = cdevsw_lookup_acquire(dev, &lc);
if (d == NULL)
return ENXIO;
+ if (d->d_devtounit) {
+ /*
+ * If the device node corresponds to an autoconf device
+ * instance, acquire a reference to it so that during
+ * d_open, device_lookup is stable.
+ *
+ * XXX This should also arrange to instantiate cloning
+ * pseudo-devices if appropriate, but that requires
+ * reviewing them all to find and verify a common
+ * pattern.
+ */
+ if ((unit = (*d->d_devtounit)(dev)) == -1)
+ return ENXIO;
+ if ((dv = device_lookup_acquire(d->d_cfdriver, unit)) == NULL)
+ return ENXIO;
+ }
+
DEV_LOCK(d);
rv = (*d->d_open)(dev, flag, devtype, l);
DEV_UNLOCK(d);
+ if (d->d_devtounit) {
+ device_release(dv);
+ }
+
cdevsw_release(d, lc);
return rv;
diff --git a/sys/sys/conf.h b/sys/sys/conf.h
index ba46976a924b..12cfd3bf89a6 100644
--- a/sys/sys/conf.h
+++ b/sys/sys/conf.h
@@ -76,6 +76,8 @@ struct bdevsw {
int (*d_dump)(dev_t, daddr_t, void *, size_t);
int (*d_psize)(dev_t);
int (*d_discard)(dev_t, off_t, off_t);
+ int (*d_devtounit)(dev_t);
+ struct cfdriver *d_cfdriver;
int d_flag;
};
@@ -94,6 +96,8 @@ struct cdevsw {
paddr_t (*d_mmap)(dev_t, off_t, int);
int (*d_kqfilter)(dev_t, struct knote *);
int (*d_discard)(dev_t, off_t, off_t);
+ int (*d_devtounit)(dev_t);
+ struct cfdriver *d_cfdriver;
int d_flag;
};
>From aa2a0c06f42afd8e250c4b240737859480edcde3 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Sat, 15 Jan 2022 19:11:10 +0000
Subject: [PATCH 06/13] disk(9): New function disklabel_dev_unit.
Maps a dev_t like wd3e to an autoconf instance number like 3, with no
partition. Same as DISKUNIT macro, but is a symbol whose pointer can
be taken. Meant for use with struct bdevsw, cdevsw::d_devtounit.
---
sys/kern/subr_disk.c | 7 +++++++
sys/sys/disklabel.h | 1 +
2 files changed, 8 insertions(+)
diff --git a/sys/kern/subr_disk.c b/sys/kern/subr_disk.c
index da664f920382..41218421db57 100644
--- a/sys/kern/subr_disk.c
+++ b/sys/kern/subr_disk.c
@@ -728,3 +728,10 @@ disk_set_info(device_t dev, struct disk *dk, const char *type)
if (odisk_info)
prop_object_release(odisk_info);
}
+
+int
+disklabel_dev_unit(dev_t dev)
+{
+
+ return DISKUNIT(dev);
+}
diff --git a/sys/sys/disklabel.h b/sys/sys/disklabel.h
index 4e94b8671332..853cdbe668a3 100644
--- a/sys/sys/disklabel.h
+++ b/sys/sys/disklabel.h
@@ -509,6 +509,7 @@ const char *convertdisklabel(struct disklabel *, void (*)(struct buf *),
int bounds_check_with_label(struct disk *, struct buf *, int);
int bounds_check_with_mediasize(struct buf *, int, uint64_t);
const char *getfstypename(int);
+int disklabel_dev_unit(dev_t);
#endif
#endif /* _LOCORE */
>From 9fcffc95ccea19b34842804bbdc5ee08597e4bf1 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Sat, 15 Jan 2022 19:18:09 +0000
Subject: [PATCH 07/13] driver(9): New function dev_minor_unit.
---
sys/kern/subr_devsw.c | 15 +++++++++++++++
sys/sys/conf.h | 1 +
2 files changed, 16 insertions(+)
diff --git a/sys/kern/subr_devsw.c b/sys/kern/subr_devsw.c
index 3bb9ed9daeeb..598436e19d18 100644
--- a/sys/kern/subr_devsw.c
+++ b/sys/kern/subr_devsw.c
@@ -1300,3 +1300,18 @@ nommap(dev_t dev, off_t off, int prot)
return (paddr_t)-1;
}
+
+/*
+ * dev_minor_unit(dev)
+ *
+ * Returns minor(dev) as an int. Intended for use with struct
+ * bdevsw, cdevsw::d_devtounit for drivers whose /dev nodes are
+ * implemented by reference to an autoconf instance with the minor
+ * number.
+ */
+int
+dev_minor_unit(dev_t dev)
+{
+
+ return minor(dev);
+}
diff --git a/sys/sys/conf.h b/sys/sys/conf.h
index 12cfd3bf89a6..cb4c287d1982 100644
--- a/sys/sys/conf.h
+++ b/sys/sys/conf.h
@@ -280,6 +280,7 @@ devmajor_t devsw_name2blk(const char *, char *, size_t);
devmajor_t devsw_name2chr(const char *, char *, size_t);
dev_t devsw_chr2blk(dev_t);
dev_t devsw_blk2chr(dev_t);
+int dev_minor_unit(dev_t);
void mm_init(void);
#endif /* _KERNEL */
>From 81eac354354126bdcfe35788747e5ddc7bd07402 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Thu, 13 Jan 2022 21:09:22 +0000
Subject: [PATCH 08/13] specfs: Wait for I/O operations in spec_node_revoke
before VOP_CLOSE.
At the point of spec_node_revoke, vp's file system is suspended,
which excludes taking the vnode lock (and doing some vnode operations
that take fstrans(9)).
But (a) not all vnode operations take the vnode lock or fstrans(9),
e.g. VOP_STRATEGY, and (b) even for some of those that do, specfs
will _unlock_ the vnode, call bdev/cdev_*, and then _relock_ the
vnode.
So we take fstrans(9) across the unlock/op/relock, and hold a new
kind of reference so that spec_node_revoke can wait until, e.g., all
concurrent calls to VOP_STRATEGY have drained.
This way, at the time spec_node_revoke calls VOP_CLOSE, we are
guaranteed that there are no more bdevsw/cdevsw operations in
progress via the vnode.
This, in turn, guarantees -- for devsw drivers that use autoconf
instances with d_devtounit -- that if xyz_detach calls vdevgone, then
when vdevgone returns, all xyz(4) devsw operations have completed and
no more can start.
P.S. This guarantee is not relevant to pseudo-devices such as cgd(4)
which call config_detach from xyzclose and thus _must not_ call
vdevgone from xyz_detach at risk of deadlock. (This change doesn't
have any impact on that deadlock.)
P.P.S. Why can't we just take the fstrans across VOP_STRATEGY and
friends? Here's an example of a deadlock arising from that -- tar
reads from USB device at sd0a which is yanked:
1. tar starts a bread, which does bbusy on some block in /dev/sd0a
2. usb2 starts to revoke /dev/sd0a when done
3. usb2 suspends / in vrevoke because that's where the /dev/sd0a vnode
lives
4. tar, in bread, issues VOP_STRATEGY on /dev/sd0a, which does
fstrans_start (or even fstrans_start_lazy), which is now waiting
for / to resume
5. usb2 starts vinvalbuf /dev/sd0a
6. usb2 is now waiting for the block on /dev/sd0a
The problem is a cycle between bbusying a block on a device whose
node happens to live on /, and suspending /.
---
sys/miscfs/specfs/spec_vnops.c | 313 ++++++++++++++++++++++-----------
sys/miscfs/specfs/specdev.h | 1 +
2 files changed, 213 insertions(+), 101 deletions(-)
diff --git a/sys/miscfs/specfs/spec_vnops.c b/sys/miscfs/specfs/spec_vnops.c
index b4bc4c34ab03..b8fef2c7014f 100644
--- a/sys/miscfs/specfs/spec_vnops.c
+++ b/sys/miscfs/specfs/spec_vnops.c
@@ -81,6 +81,7 @@ __KERNEL_RCSID(0, "$NetBSD: spec_vnops.c,v 1.183 2021/07/18 23:57:14 dholland Ex
#include <sys/kauth.h>
#include <sys/fstrans.h>
#include <sys/module.h>
+#include <sys/atomic.h>
#include <miscfs/genfs/genfs.h>
#include <miscfs/specfs/specdev.h>
@@ -103,6 +104,7 @@ const char devcls[] = "devcls";
static vnode_t *specfs_hash[SPECHSZ];
extern struct mount *dead_rootmount;
+static struct kcondvar specfs_iocv;
/*
* This vnode operations vector is used for special device nodes
@@ -210,6 +212,100 @@ spec_init(void)
rawio_listener = kauth_listen_scope(KAUTH_SCOPE_DEVICE,
rawio_listener_cb, NULL);
+ cv_init(&specfs_iocv, "specio");
+}
+
+/*
+ * spec_io_enter(vp, &sn, &dev)
+ *
+ * Enter an operation that may not hold vp's vnode lock or an
+ * fstrans on vp's mount. Until spec_io_exit, the vnode will not
+ * be revoked.
+ *
+ * On success, set sn to the specnode pointer and dev to the dev_t
+ * number and return zero. Caller must later call spec_io_exit
+ * when done.
+ *
+ * On failure, return ENXIO -- the device has been revoked and no
+ * longer exists.
+ */
+static int
+spec_io_enter(struct vnode *vp, struct specnode **snp, dev_t *devp)
+{
+ dev_t dev;
+ struct specnode *sn;
+ unsigned iocnt;
+ int error = 0;
+
+ mutex_enter(vp->v_interlock);
+
+ /*
+ * Extract all the info we need from the vnode, unless the
+ * vnode has already been reclaimed. This can happen if the
+ * underlying device has been removed and all the device nodes
+ * for it have been revoked. The caller may not hold a vnode
+ * lock or fstrans to prevent this from happening before it has
+ * had an opportunity to notice the vnode is dead.
+ */
+ if (vdead_check(vp, VDEAD_NOWAIT) != 0 ||
+ (sn = vp->v_specnode) == NULL ||
+ (dev = vp->v_rdev) == NODEV) {
+ error = ENXIO;
+ goto out;
+ }
+
+ /*
+ * Notify spec_node_revoke that we are doing an I/O operation
+ * which may not be not bracketed by fstrans(9) and thus is not
+ * blocked by vfs suspension.
+ *
+ * We could hold this reference with psref(9) instead, but we
+ * already have to take the interlock for vdead_check, so
+ * there's not much more cost here to another atomic operation.
+ */
+ iocnt = atomic_inc_uint_nv(&sn->sn_iocnt);
+ CTASSERT(MAXLWP < UINT_MAX);
+ KASSERT(iocnt < UINT_MAX);
+
+ /* Success! */
+ *snp = sn;
+ *devp = dev;
+ error = 0;
+
+out: mutex_exit(vp->v_interlock);
+ return error;
+}
+
+/*
+ * spec_io_exit(vp, sn)
+ *
+ * Exit an operation entered with a successful spec_io_enter --
+ * allow concurrent spec_node_revoke to proceed. The argument sn
+ * must match the struct specnode pointer returned by spec_io_exit
+ * for vp.
+ */
+static void
+spec_io_exit(struct vnode *vp, struct specnode *sn)
+{
+ unsigned iocnt;
+
+ KASSERT(vp->v_specnode == sn);
+
+ /*
+ * We are done. Notify spec_node_revoke if appropriate. The
+ * transition of 1 -> 0 must happen under device_lock so
+ * spec_node_revoke doesn't miss a wakeup.
+ */
+ do {
+ iocnt = atomic_load_relaxed(&sn->sn_iocnt);
+ if (iocnt == 1) {
+ mutex_enter(&device_lock);
+ if (atomic_dec_uint_nv(&sn->sn_iocnt) == 0)
+ cv_broadcast(&specfs_iocv);
+ mutex_exit(&device_lock);
+ break;
+ }
+ } while (atomic_cas_uint(&sn->sn_iocnt, iocnt, iocnt - 1) != iocnt);
}
/*
@@ -261,6 +357,7 @@ spec_node_init(vnode_t *vp, dev_t rdev)
sn->sn_opencnt = 0;
sn->sn_rdev = rdev;
sn->sn_gone = false;
+ sn->sn_iocnt = 0;
vp->v_specnode = sn;
vp->v_specnext = *vpp;
*vpp = vp;
@@ -406,7 +503,22 @@ spec_node_revoke(vnode_t *vp)
if (sn->sn_opencnt != 0) {
sd->sd_opencnt -= (sn->sn_opencnt - 1);
sn->sn_opencnt = 1;
+
+ /* Prevent new opens. */
sn->sn_gone = true;
+
+ /*
+ * Wait for all I/O operations in spec_io_enter/exit to
+ * complete. The caller holds the file system
+ * suspended, but file system suspension doesn't block
+ * all device special operations -- only those that run
+ * to completion holding the vnode lock and a handful
+ * of others. It is the driver's responsibility to
+ * ensure that new opens fail gracefully at this point.
+ */
+ while (atomic_load_relaxed(&sn->sn_iocnt) != 0)
+ cv_wait(&specfs_iocv, &device_lock);
+
mutex_exit(&device_lock);
VOP_CLOSE(vp, FNONBLOCK, NOCRED);
@@ -435,6 +547,7 @@ spec_node_destroy(vnode_t *vp)
KASSERT(vp->v_type == VBLK || vp->v_type == VCHR);
KASSERT(vp->v_specnode != NULL);
KASSERT(sn->sn_opencnt == 0);
+ KASSERT(sn->sn_iocnt == 0);
mutex_enter(&device_lock);
/* Remove from the hash and destroy the node. */
@@ -690,6 +803,7 @@ spec_read(void *v)
struct vnode *vp = ap->a_vp;
struct uio *uio = ap->a_uio;
struct lwp *l = curlwp;
+ dev_t dev;
struct buf *bp;
daddr_t bn;
int bsize, bscale;
@@ -701,28 +815,32 @@ spec_read(void *v)
int *rasizes;
int nrablks, ratogo;
+ KASSERT(VOP_ISLOCKED(vp) || (vp->v_vflag & VV_LOCKSWORK) == 0);
KASSERT(uio->uio_rw == UIO_READ);
KASSERTMSG(VMSPACE_IS_KERNEL_P(uio->uio_vmspace) ||
uio->uio_vmspace == curproc->p_vmspace,
"vmspace belongs to neither kernel nor curproc");
if (uio->uio_resid == 0)
- return (0);
+ return 0;
- switch (vp->v_type) {
+ dev = vp->v_rdev;
+ switch (vp->v_type) {
case VCHR:
+ fstrans_start(vp->v_mount);
VOP_UNLOCK(vp);
- error = cdev_read(vp->v_rdev, uio, ap->a_ioflag);
+ error = cdev_read(dev, uio, ap->a_ioflag);
vn_lock(vp, LK_SHARED | LK_RETRY);
- return (error);
+ fstrans_done(vp->v_mount);
+ return error;
case VBLK:
KASSERT(vp == vp->v_specnode->sn_dev->sd_bdevvp);
if (uio->uio_offset < 0)
- return (EINVAL);
+ return EINVAL;
- if (bdev_ioctl(vp->v_rdev, DIOCGPARTINFO, &pi, FREAD, l) == 0)
+ if (bdev_ioctl(dev, DIOCGPARTINFO, &pi, FREAD, l) == 0)
bsize = imin(imax(pi.pi_bsize, DEV_BSIZE), MAXBSIZE);
else
bsize = BLKDEV_IOSIZE;
@@ -767,7 +885,7 @@ spec_read(void *v)
kmem_free(rablks, nra * sizeof(*rablks));
kmem_free(rasizes, nra * sizeof(*rasizes));
- return (error);
+ return error;
default:
panic("spec_read type");
@@ -790,6 +908,7 @@ spec_write(void *v)
} */ *ap = v;
struct vnode *vp = ap->a_vp;
struct uio *uio = ap->a_uio;
+ dev_t dev;
struct lwp *l = curlwp;
struct buf *bp;
daddr_t bn;
@@ -798,27 +917,32 @@ spec_write(void *v)
int n, on;
int error = 0;
+ KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE ||
+ (vp->v_vflag & VV_LOCKSWORK) == 0);
KASSERT(uio->uio_rw == UIO_WRITE);
KASSERTMSG(VMSPACE_IS_KERNEL_P(uio->uio_vmspace) ||
uio->uio_vmspace == curproc->p_vmspace,
"vmspace belongs to neither kernel nor curproc");
- switch (vp->v_type) {
+ dev = vp->v_rdev;
+ switch (vp->v_type) {
case VCHR:
+ fstrans_start(vp->v_mount);
VOP_UNLOCK(vp);
- error = cdev_write(vp->v_rdev, uio, ap->a_ioflag);
+ error = cdev_write(dev, uio, ap->a_ioflag);
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
- return (error);
+ fstrans_done(vp->v_mount);
+ return error;
case VBLK:
KASSERT(vp == vp->v_specnode->sn_dev->sd_bdevvp);
if (uio->uio_resid == 0)
- return (0);
+ return 0;
if (uio->uio_offset < 0)
- return (EINVAL);
+ return EINVAL;
- if (bdev_ioctl(vp->v_rdev, DIOCGPARTINFO, &pi, FREAD, l) == 0)
+ if (bdev_ioctl(dev, DIOCGPARTINFO, &pi, FREAD, l) == 0)
bsize = imin(imax(pi.pi_bsize, DEV_BSIZE), MAXBSIZE);
else
bsize = BLKDEV_IOSIZE;
@@ -866,31 +990,23 @@ spec_fdiscard(void *v)
off_t a_pos;
off_t a_len;
} */ *ap = v;
- struct vnode *vp;
+ struct vnode *vp = ap->a_vp;
dev_t dev;
- vp = ap->a_vp;
- dev = NODEV;
-
- mutex_enter(vp->v_interlock);
- if (vdead_check(vp, VDEAD_NOWAIT) == 0 && vp->v_specnode != NULL) {
- dev = vp->v_rdev;
- }
- mutex_exit(vp->v_interlock);
+ KASSERT(VOP_ISLOCKED(vp) == LK_EXCLUSIVE ||
+ (vp->v_vflag & VV_LOCKSWORK) == 0);
- if (dev == NODEV) {
- return ENXIO;
- }
+ dev = vp->v_rdev;
switch (vp->v_type) {
- case VCHR:
+ case VCHR:
// this is not stored for character devices
//KASSERT(vp == vp->v_specnode->sn_dev->sd_cdevvp);
return cdev_discard(dev, ap->a_pos, ap->a_len);
- case VBLK:
+ case VBLK:
KASSERT(vp == vp->v_specnode->sn_dev->sd_bdevvp);
return bdev_discard(dev, ap->a_pos, ap->a_len);
- default:
+ default:
panic("spec_fdiscard: not a device\n");
}
}
@@ -909,40 +1025,32 @@ spec_ioctl(void *v)
int a_fflag;
kauth_cred_t a_cred;
} */ *ap = v;
- struct vnode *vp;
+ struct vnode *vp = ap->a_vp;
+ struct specnode *sn;
dev_t dev;
+ int error;
- /*
- * Extract all the info we need from the vnode, taking care to
- * avoid a race with VOP_REVOKE().
- */
-
- vp = ap->a_vp;
- dev = NODEV;
- mutex_enter(vp->v_interlock);
- if (vdead_check(vp, VDEAD_NOWAIT) == 0 && vp->v_specnode) {
- dev = vp->v_rdev;
- }
- mutex_exit(vp->v_interlock);
- if (dev == NODEV) {
- return ENXIO;
- }
+ error = spec_io_enter(vp, &sn, &dev);
+ if (error)
+ return error;
switch (vp->v_type) {
-
case VCHR:
- return cdev_ioctl(dev, ap->a_command, ap->a_data,
+ error = cdev_ioctl(dev, ap->a_command, ap->a_data,
ap->a_fflag, curlwp);
-
+ break;
case VBLK:
KASSERT(vp == vp->v_specnode->sn_dev->sd_bdevvp);
- return bdev_ioctl(dev, ap->a_command, ap->a_data,
+ error = bdev_ioctl(dev, ap->a_command, ap->a_data,
ap->a_fflag, curlwp);
-
+ break;
default:
panic("spec_ioctl");
/* NOTREACHED */
}
+
+ spec_io_exit(vp, sn);
+ return error;
}
/* ARGSUSED */
@@ -953,33 +1061,25 @@ spec_poll(void *v)
struct vnode *a_vp;
int a_events;
} */ *ap = v;
- struct vnode *vp;
+ struct vnode *vp = ap->a_vp;
+ struct specnode *sn;
dev_t dev;
+ int revents;
- /*
- * Extract all the info we need from the vnode, taking care to
- * avoid a race with VOP_REVOKE().
- */
-
- vp = ap->a_vp;
- dev = NODEV;
- mutex_enter(vp->v_interlock);
- if (vdead_check(vp, VDEAD_NOWAIT) == 0 && vp->v_specnode) {
- dev = vp->v_rdev;
- }
- mutex_exit(vp->v_interlock);
- if (dev == NODEV) {
+ if (spec_io_enter(vp, &sn, &dev) != 0)
return POLLERR;
- }
switch (vp->v_type) {
-
case VCHR:
- return cdev_poll(dev, ap->a_events, curlwp);
-
+ revents = cdev_poll(dev, ap->a_events, curlwp);
+ break;
default:
- return (genfs_poll(v));
+ revents = genfs_poll(v);
+ break;
}
+
+ spec_io_exit(vp, sn);
+ return revents;
}
/* ARGSUSED */
@@ -990,20 +1090,30 @@ spec_kqfilter(void *v)
struct vnode *a_vp;
struct proc *a_kn;
} */ *ap = v;
+ struct vnode *vp = ap->a_vp;
+ struct specnode *sn;
dev_t dev;
+ int error;
- switch (ap->a_vp->v_type) {
+ error = spec_io_enter(vp, &sn, &dev);
+ if (error)
+ return error;
+ switch (vp->v_type) {
case VCHR:
- dev = ap->a_vp->v_rdev;
- return cdev_kqfilter(dev, ap->a_kn);
+ error = cdev_kqfilter(dev, ap->a_kn);
+ break;
default:
/*
* Block devices don't support kqfilter, and refuse it
* for any other files (like those vflush()ed) too.
*/
- return (EOPNOTSUPP);
+ error = EOPNOTSUPP;
+ break;
}
+
+ spec_io_exit(vp, sn);
+ return error;
}
/*
@@ -1018,11 +1128,19 @@ spec_mmap(void *v)
kauth_cred_t a_cred;
} */ *ap = v;
struct vnode *vp = ap->a_vp;
+ struct specnode *sn;
+ dev_t dev;
+ int error;
+
+ error = spec_io_enter(vp, &sn, &dev);
+ if (error)
+ return error;
KASSERT(vp->v_type == VBLK);
- if (bdev_type(vp->v_rdev) != D_DISK)
+ if (bdev_type(dev) != D_DISK)
return EINVAL;
+ spec_io_exit(vp, sn);
return 0;
}
@@ -1067,27 +1185,15 @@ spec_strategy(void *v)
} */ *ap = v;
struct vnode *vp = ap->a_vp;
struct buf *bp = ap->a_bp;
+ struct specnode *sn;
dev_t dev;
+ bool ioentered = false;
int error;
- dev = NODEV;
-
- /*
- * Extract all the info we need from the vnode, taking care to
- * avoid a race with VOP_REVOKE().
- */
-
- mutex_enter(vp->v_interlock);
- if (vdead_check(vp, VDEAD_NOWAIT) == 0 && vp->v_specnode != NULL) {
- KASSERT(vp == vp->v_specnode->sn_dev->sd_bdevvp);
- dev = vp->v_rdev;
- }
- mutex_exit(vp->v_interlock);
-
- if (dev == NODEV) {
- error = ENXIO;
+ error = spec_io_enter(vp, &sn, &dev);
+ if (error)
goto out;
- }
+ ioentered = true;
bp->b_dev = dev;
if (!(bp->b_flags & B_READ)) {
@@ -1106,14 +1212,15 @@ spec_strategy(void *v)
goto out;
}
bdev_strategy(bp);
-
- return 0;
-
-out:
- bp->b_error = error;
- bp->b_resid = bp->b_bcount;
- biodone(bp);
-
+ error = 0;
+
+out: if (ioentered)
+ spec_io_exit(vp, sn);
+ if (error) {
+ bp->b_error = error;
+ bp->b_resid = bp->b_bcount;
+ biodone(bp);
+ }
return error;
}
@@ -1284,18 +1391,22 @@ spec_close(void *v)
* might end up sleeping for someone else who wants our queues. They
* won't get them if we hold the vnode locked.
*/
- if (!(flags & FNONBLOCK))
+ if (!(flags & FNONBLOCK)) {
+ fstrans_start(vp->v_mount);
VOP_UNLOCK(vp);
+ }
if (vp->v_type == VBLK)
error = bdev_close(dev, flags, mode, curlwp);
else
error = cdev_close(dev, flags, mode, curlwp);
- if (!(flags & FNONBLOCK))
+ if (!(flags & FNONBLOCK)) {
vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+ fstrans_done(vp->v_mount);
+ }
- return (error);
+ return error;
}
/*
diff --git a/sys/miscfs/specfs/specdev.h b/sys/miscfs/specfs/specdev.h
index 621c103e80b1..e8afc0606db9 100644
--- a/sys/miscfs/specfs/specdev.h
+++ b/sys/miscfs/specfs/specdev.h
@@ -69,6 +69,7 @@ typedef struct specnode {
u_int sn_opencnt;
dev_t sn_rdev;
bool sn_gone;
+ volatile u_int sn_iocnt; /* # active I/O operations */
} specnode_t;
typedef struct specdev {
>From d723d6c49373412d817d62cb8f03e68f3a033d5d Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Fri, 14 Jan 2022 21:33:14 +0000
Subject: [PATCH 09/13] uhid(4): Use d_cfdriver/devtounit to avoid open/detach
races.
---
sys/dev/usb/uhid.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/sys/dev/usb/uhid.c b/sys/dev/usb/uhid.c
index 81292fd5130e..46769dc0353a 100644
--- a/sys/dev/usb/uhid.c
+++ b/sys/dev/usb/uhid.c
@@ -134,6 +134,8 @@ const struct cdevsw uhid_cdevsw = {
.d_mmap = nommap,
.d_kqfilter = uhidkqfilter,
.d_discard = nodiscard,
+ .d_cfdriver = &uhid_cd,
+ .d_devtounit = dev_minor_unit,
.d_flag = D_OTHER
};
>From 95d1d0648c4f3d95abc37e75f4afd7a25cb1c987 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Sat, 15 Jan 2022 19:29:39 +0000
Subject: [PATCH 10/13] wd(4): Use d_cfdriver/devtounit to avoid open/detach
races.
---
sys/dev/ata/wd.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/sys/dev/ata/wd.c b/sys/dev/ata/wd.c
index b5d7476d1e6c..672684a3b4aa 100644
--- a/sys/dev/ata/wd.c
+++ b/sys/dev/ata/wd.c
@@ -152,6 +152,8 @@ const struct bdevsw wd_bdevsw = {
.d_dump = wddump,
.d_psize = wdsize,
.d_discard = wddiscard,
+ .d_cfdriver = &wd_cd,
+ .d_devtounit = disklabel_dev_unit,
.d_flag = D_DISK
};
@@ -167,6 +169,8 @@ const struct cdevsw wd_cdevsw = {
.d_mmap = nommap,
.d_kqfilter = nokqfilter,
.d_discard = wddiscard,
+ .d_cfdriver = &wd_cd,
+ .d_devtounit = disklabel_dev_unit,
.d_flag = D_DISK
};
>From 03f101fb4307d64d6e2f528cbad942323de5a350 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Sat, 15 Jan 2022 19:30:21 +0000
Subject: [PATCH 11/13] sd(4): Use d_cfdriver/devtounit to avoid open/detach
races.
---
sys/dev/scsipi/sd.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/sys/dev/scsipi/sd.c b/sys/dev/scsipi/sd.c
index 7bd0d12c070b..24b3b6c1aa9c 100644
--- a/sys/dev/scsipi/sd.c
+++ b/sys/dev/scsipi/sd.c
@@ -167,6 +167,8 @@ const struct bdevsw sd_bdevsw = {
.d_dump = sddump,
.d_psize = sdsize,
.d_discard = nodiscard,
+ .d_cfdriver = &sd_cd,
+ .d_devtounit = disklabel_dev_unit,
.d_flag = D_DISK | D_MPSAFE
};
@@ -182,6 +184,8 @@ const struct cdevsw sd_cdevsw = {
.d_mmap = nommap,
.d_kqfilter = nokqfilter,
.d_discard = nodiscard,
+ .d_cfdriver = &sd_cd,
+ .d_devtounit = disklabel_dev_unit,
.d_flag = D_DISK | D_MPSAFE
};
>From 10f326959fe1b522307df05635a2b2868ffab5ac Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Sat, 15 Jan 2022 19:55:02 +0000
Subject: [PATCH 12/13] audio(4): Use d_cfdriver/devtounit to avoid open/detach
races.
---
sys/dev/audio/audio.c | 81 +++++++++++++++++--------------------------
1 file changed, 32 insertions(+), 49 deletions(-)
diff --git a/sys/dev/audio/audio.c b/sys/dev/audio/audio.c
index d22ea989a180..176749ac449f 100644
--- a/sys/dev/audio/audio.c
+++ b/sys/dev/audio/audio.c
@@ -521,7 +521,6 @@ static int audio_exlock_mutex_enter(struct audio_softc *);
static void audio_exlock_mutex_exit(struct audio_softc *);
static int audio_exlock_enter(struct audio_softc *);
static void audio_exlock_exit(struct audio_softc *);
-static void audio_sc_acquire_foropen(struct audio_softc *, struct psref *);
static struct audio_softc *audio_sc_acquire_fromfile(audio_file_t *,
struct psref *);
static void audio_sc_release(struct audio_softc *, struct psref *);
@@ -732,6 +731,8 @@ const struct cdevsw audio_cdevsw = {
.d_mmap = nommap,
.d_kqfilter = nokqfilter,
.d_discard = nodiscard,
+ .d_cfdriver = &audio_cd,
+ .d_devtounit = dev_minor_unit,
.d_flag = D_OTHER | D_MPSAFE
};
@@ -1543,31 +1544,6 @@ audio_exlock_exit(struct audio_softc *sc)
audio_exlock_mutex_exit(sc);
}
-/*
- * Increment reference counter for this sc.
- * This is intended to be used for open.
- */
-void
-audio_sc_acquire_foropen(struct audio_softc *sc, struct psref *refp)
-{
- int s;
-
- /* Block audiodetach while we acquire a reference */
- s = pserialize_read_enter();
-
- /*
- * We don't examine sc_dying here. However, all open methods
- * call audio_exlock_enter() right after this, so we can examine
- * sc_dying in it.
- */
-
- /* Acquire a reference */
- psref_acquire(refp, &sc->sc_psref, audio_psref_class);
-
- /* Now sc won't go away until we drop the reference count */
- pserialize_read_exit(s);
-}
-
/*
* Get sc from file, and increment reference counter for this sc.
* This is intended to be used for methods other than open.
@@ -1680,21 +1656,20 @@ static int
audioopen(dev_t dev, int flags, int ifmt, struct lwp *l)
{
struct audio_softc *sc;
- struct psref sc_ref;
- int bound;
int error;
- /* Find the device */
+ /*
+ * Find the device. Because we wired the cdevsw to the audio
+ * autoconf instance, the system ensures it will not go away
+ * until after we return.
+ */
sc = device_lookup_private(&audio_cd, AUDIOUNIT(dev));
if (sc == NULL || sc->hw_if == NULL)
return ENXIO;
- bound = curlwp_bind();
- audio_sc_acquire_foropen(sc, &sc_ref);
-
error = audio_exlock_enter(sc);
if (error)
- goto done;
+ return error;
device_active(sc->sc_dev, DVA_SYSTEM);
switch (AUDIODEV(dev)) {
@@ -1714,9 +1689,6 @@ audioopen(dev_t dev, int flags, int ifmt, struct lwp *l)
}
audio_exlock_exit(sc);
-done:
- audio_sc_release(sc, &sc_ref);
- curlwp_bindx(bound);
return error;
}
@@ -2098,30 +2070,41 @@ done:
int
audiobellopen(dev_t dev, audio_file_t **filep)
{
+ device_t audiodev = NULL;
struct audio_softc *sc;
- struct psref sc_ref;
- int bound;
+ bool exlock = false;
int error;
- /* Find the device */
- sc = device_lookup_private(&audio_cd, AUDIOUNIT(dev));
- if (sc == NULL || sc->hw_if == NULL)
- return ENXIO;
+ /*
+ * Find the autoconf instance and make sure it doesn't go away
+ * while we are opening it.
+ */
+ audiodev = device_lookup_acquire(&audio_cd, AUDIOUNIT(dev));
+ if (audiodev == NULL) {
+ error = ENXIO;
+ goto out;
+ }
- bound = curlwp_bind();
- audio_sc_acquire_foropen(sc, &sc_ref);
+ /* If attach failed, it's hopeless -- give up. */
+ sc = device_private(audiodev);
+ if (sc->hw_if == NULL) {
+ error = ENXIO;
+ goto out;
+ }
+ /* Take the exclusive configuration lock. */
error = audio_exlock_enter(sc);
if (error)
- goto done;
+ goto out;
+ /* Open the audio device. */
device_active(sc->sc_dev, DVA_SYSTEM);
error = audio_open(dev, sc, FWRITE, 0, curlwp, filep);
- audio_exlock_exit(sc);
-done:
- audio_sc_release(sc, &sc_ref);
- curlwp_bindx(bound);
+out: if (exlock)
+ audio_exlock_exit(sc);
+ if (audiodev)
+ device_release(audiodev);
return error;
}
>From 5798bbdaa473dbaf21ae560d6eb5e414ce707fb0 Mon Sep 17 00:00:00 2001
From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
Date: Sat, 15 Jan 2022 19:55:27 +0000
Subject: [PATCH 13/13] uhid(4): Omit needless reference-counting goo.
vdevgone now guarantees devsw operations have drained and the device
has been closed.
---
sys/dev/usb/uhid.c | 38 --------------------------------------
1 file changed, 38 deletions(-)
diff --git a/sys/dev/usb/uhid.c b/sys/dev/usb/uhid.c
index 46769dc0353a..1e6cd705e1a9 100644
--- a/sys/dev/usb/uhid.c
+++ b/sys/dev/usb/uhid.c
@@ -104,7 +104,6 @@ struct uhid_softc {
volatile uint32_t sc_state; /* driver state */
#define UHID_IMMED 0x02 /* return read data immediately */
- int sc_refcnt;
int sc_raw;
u_char sc_open;
u_char sc_dying;
@@ -196,7 +195,6 @@ uhid_attach(device_t parent, device_t self, void *aux)
mutex_init(&sc->sc_lock, MUTEX_DEFAULT, IPL_SOFTUSB);
cv_init(&sc->sc_cv, "uhidrea");
- cv_init(&sc->sc_detach_cv, "uhiddet");
if (!pmf_device_register(self, NULL, NULL))
aprint_error_dev(self, "couldn't establish power handler\n");
@@ -235,15 +233,6 @@ uhid_detach(device_t self, int flags)
/* Interrupt any pending uhidev_write. */
uhidev_stop(&sc->sc_hdev);
- /* Wait for I/O operations to complete. */
- mutex_enter(&sc->sc_lock);
- while (sc->sc_refcnt) {
- DPRINTF(("%s: open=%d refcnt=%d\n", __func__,
- sc->sc_open, sc->sc_refcnt));
- cv_wait(&sc->sc_detach_cv, &sc->sc_lock);
- }
- mutex_exit(&sc->sc_lock);
-
pmf_device_deregister(self);
/* locate the major number */
@@ -253,28 +242,9 @@ uhid_detach(device_t self, int flags)
mn = device_unit(self);
vdevgone(maj, mn, mn, VCHR);
- /*
- * Wait for close to finish.
- *
- * XXX I assumed that vdevgone would synchronously call close,
- * and not return before it has completed, but empirically the
- * assertion of sc->sc_open == 0 below fires if we don't wait
- * here. Someone^TM should carefully examine vdevgone to
- * ascertain what it guarantees, and audit all other users of
- * it accordingly.
- */
- mutex_enter(&sc->sc_lock);
- while (sc->sc_open) {
- DPRINTF(("%s: open=%d\n", __func__, sc->sc_open));
- cv_wait(&sc->sc_detach_cv, &sc->sc_lock);
- }
- mutex_exit(&sc->sc_lock);
-
KASSERT(sc->sc_open == 0);
- KASSERT(sc->sc_refcnt == 0);
cv_destroy(&sc->sc_cv);
- cv_destroy(&sc->sc_detach_cv);
mutex_destroy(&sc->sc_lock);
seldestroy(&sc->sc_rsel);
@@ -391,7 +361,6 @@ fail1: selnotify(&sc->sc_rsel, POLLHUP, 0);
fail0: mutex_enter(&sc->sc_lock);
KASSERT(sc->sc_open == 1);
sc->sc_open = 0;
- cv_broadcast(&sc->sc_detach_cv);
atomic_store_relaxed(&sc->sc_state, 0);
mutex_exit(&sc->sc_lock);
return error;
@@ -434,7 +403,6 @@ uhidclose(dev_t dev, int flag, int mode, struct lwp *l)
mutex_enter(&sc->sc_lock);
KASSERT(sc->sc_open == 1);
sc->sc_open = 0;
- cv_broadcast(&sc->sc_detach_cv);
atomic_store_relaxed(&sc->sc_state, 0);
mutex_exit(&sc->sc_lock);
@@ -456,11 +424,8 @@ uhid_enter(dev_t dev, struct uhid_softc **scp)
KASSERT(sc->sc_open == 2);
if (sc->sc_dying) {
error = ENXIO;
- } else if (sc->sc_refcnt == INT_MAX) {
- error = EBUSY;
} else {
*scp = sc;
- sc->sc_refcnt++;
error = 0;
}
mutex_exit(&sc->sc_lock);
@@ -474,9 +439,6 @@ uhid_exit(struct uhid_softc *sc)
mutex_enter(&sc->sc_lock);
KASSERT(sc->sc_open == 2);
- KASSERT(sc->sc_refcnt > 0);
- if (--sc->sc_refcnt == 0)
- cv_broadcast(&sc->sc_detach_cv);
mutex_exit(&sc->sc_lock);
}
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