Re: kern/46462: Hang trying to run a disklabel on an inserted USB flash drive

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

The following reply was made to PR kern/46462; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: Mindaugas Rasiukevicius <rmind%NetBSD.org@localhost>
Cc: gnats-bugs%NetBSD.org@localhost, kern-bug-people%NetBSD.org@localhost, 
gnats-admin%NetBSD.org@localhost,
        netbsd-bugs%NetBSD.org@localhost, cyber%NetBSD.org@localhost
Subject: Re: kern/46462: Hang trying to run a disklabel on an inserted USB
 flash drive
Date: Mon, 21 May 2012 14:45:47 +0200

 On Sat, May 19, 2012 at 08:29:03PM +0100, Mindaugas Rasiukevicius wrote:
 > OK, this thread is likely a problem:
 > 
 > > db> tr/t 0.59
 > > trace: pid 0 lid 59 at 0xffffa00049c1b770
 > > sleepq_block() at netbsd:sleepq_block+0xdd
 > > cv_wait() at netbsd:cv_wait+0xf1
 > > biowait() at netbsd:biowait+0x4f
 > > read_sector() at netbsd:read_sector+0x23
 > > scan_mbr() at netbsd:scan_mbr+0x40
 > > readdisklabel() at netbsd:readdisklabel+0xfb
 > > sdopen() at netbsd:sdopen+0x26a
 > > spec_open() at netbsd:spec_open+0x29a
 > > VOP_OPEN() at netbsd:VOP_OPEN+0x29
 > > dkwedge_discover() at netbsd:dkwedge_discover+0xee
 > > sdattach() at netbsd:sdattach+0x206
 > > config_attach_loc() at netbsd:config_attach_loc+0x15a
 > > scsi_probe_bus() at netbsd:scsi_probe_bus+0x4aa
 > > scsibus_config() at netbsd:scsibus_config+0x5d
 > > scsipi_completion_thread() at netbsd:scsipi_completion_thread+0x23
 > 
 > - scsipi_completion_thread()
 >      This asynchronous completion thread handles the event, which is
 >      in this case attaching of a new device.  Callbacks are performed
 >      under splbio().
 > 
 > -- [skipping] .. sdopen()
 >      Acquiring sd->sc_dk.dk_openlock here.  We are still at IPL_BIO.
 > 
 > --- [skipping] .. read_sector() -> disk_read_sectors()
 >      Invoking sdstrategy() and entering biowait().  However, since
 >      we are still at IPL_BIO, biodone() does not happen - thread has
 >      deadlocked against interrupt with sd->sc_dk.dk_openlock held.
 
 I don't understand how you get to this conclusion. biowait() will cause the
 thread to sleep, and IPL_BIO interrupts will be accepted again while
 it sleeps. Otherwise, all IPL_VM and lower interrupts would be blocked,
 which would probably cause not only disklabel to hang, but most probably
 the complete system.
 
 I guess the problem is more that the USB I/O doesn't completes for some
 reason.
 
 -- 
 Manuel Bouyer <bouyer%antioche.eu.org@localhost>
      NetBSD: 26 ans d'experience feront toujours la difference
 --