[src/trunk]: src/sys/kern entropy: Use a separate condvar for rndsource list ...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/bb3d8363da47
branches:  trunk
changeset: 949418:bb3d8363da47
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Wed Jan 13 23:53:23 2021 +0000

description:
entropy: Use a separate condvar for rndsource list lock.

Otherwise, two processes both waiting for entropy will dance around
waking each other up (by releasing the rndsource list lock) and going
back to sleep (waiting for entropy).

Witnessed on the armv7 testbed when /etc/security presumably ran
twice over a >day-long test, until the metaphorical plug got pulled:

net/if_ipsec/t_ipsec_natt (509/888): 2 test cases
    ipsecif_natt_transport_null: [ 37123.2631856] entropy: pid 1005 (dd) blocking due to lack of entropy
[256.523317s] Failed: atf-check failed; see the output of the test for details
    ipsecif_natt_transport_rijndaelcbc: [274.370791s] Failed: atf-check failed; see the output of the test for details
[532.486697s]
...
    puffs_lstat_symlink: [ 123442.1606517] entropy: pid 9499 (dd) blocking due to lack of entropy
[ 123442.1835067] entropy: pid 1005 (dd) blocking due to lack of entropy
[ 123442.1944600] entropy: pid 9499 (dd) blocking due to lack of entropy
[ 123442.1944600] entropy: pid 1005 (dd) blocking due to lack of entropy
...

diffstat:

 sys/kern/kern_entropy.c |  12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diffs (61 lines):

diff -r 2aebd5cf4dff -r bb3d8363da47 sys/kern/kern_entropy.c
--- a/sys/kern/kern_entropy.c   Wed Jan 13 19:46:49 2021 +0000
+++ b/sys/kern/kern_entropy.c   Wed Jan 13 23:53:23 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_entropy.c,v 1.26 2021/01/11 02:18:40 riastradh Exp $      */
+/*     $NetBSD: kern_entropy.c,v 1.27 2021/01/13 23:53:23 riastradh Exp $      */
 
 /*-
  * Copyright (c) 2019 The NetBSD Foundation, Inc.
@@ -75,7 +75,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.26 2021/01/11 02:18:40 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_entropy.c,v 1.27 2021/01/13 23:53:23 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -161,6 +161,7 @@
        kcondvar_t      cv;             /* notifies state changes */
        struct selinfo  selq;           /* notifies needed -> 0 */
        struct lwp      *sourcelock;    /* lock on list of sources */
+       kcondvar_t      sourcelock_cv;  /* notifies sourcelock release */
        LIST_HEAD(,krndsource) sources; /* list of entropy sources */
        enum entropy_stage {
                ENTROPY_COLD = 0, /* single-threaded */
@@ -367,6 +368,7 @@
        mutex_init(&E->lock, MUTEX_DEFAULT, IPL_VM);
        cv_init(&E->cv, "entropy");
        selinit(&E->selq);
+       cv_init(&E->sourcelock_cv, "entsrclock");
 
        /* Make sure the seed source is attached.  */
        attach_seed_rndsource();
@@ -1594,7 +1596,7 @@
        /* Wait until the source list is not in use, and remove it.  */
        mutex_enter(&E->lock);
        while (E->sourcelock)
-               cv_wait(&E->cv, &E->lock);
+               cv_wait(&E->sourcelock_cv, &E->lock);
        LIST_REMOVE(rs, list);
        mutex_exit(&E->lock);
 
@@ -1618,7 +1620,7 @@
        KASSERT(mutex_owned(&E->lock));
 
        while (E->sourcelock) {
-               error = cv_wait_sig(&E->cv, &E->lock);
+               error = cv_wait_sig(&E->sourcelock_cv, &E->lock);
                if (error)
                        return error;
        }
@@ -1663,7 +1665,7 @@
            curlwp, E->sourcelock);
        E->sourcelock = NULL;
        if (E->stage >= ENTROPY_WARM)
-               cv_broadcast(&E->cv);
+               cv_signal(&E->sourcelock_cv);
 }
 
 /*