On Friday 18 August 2006 15:26, Alex Unleashed wrote:
> Hello,
>
> Before anything else I'd like to say I'm working on a SoC project for
> Gentoo for which I have to port a sandbox-like application wrapper (in
> userspace) to FreeBSD, which deals with the building and installing of
> software so that nothing gets screwed in the filesystem. It's
> finished, but unfortunately it gets frozen at random points,
> preventing the system from launching new programs or saving to disk,
> which suggested a kernel bug, as was later confirmed looking at the
> waitchannels and debugging. I know there is someone working out issues
> in devfs code in 6.x, so this might also be interesting to him.
>
> I've been able to reproduce both in 6.1-RELEASE-p3 and 6-STABLE
> (snapshot from August 16th ~01:00 GMT) a deadlock in devfs code which
> leaves the system unable to access the disk. I've come up with some
> interesting debugging info, and it looks to me like there are vnode
> problems while a sx lock is being held.
>
> My take at it is that the deadlock occurs when a process gets a lock
> on a vnode (tagged "devfs") and another process xlocks an sx lock
> ("devfsmount"). For some reason the one holding the sx lock wants to
> get the lock on the vnode through devfs_allocv(), and the other
> process wants to get the sx lock through devfs_lookup(). From this
> point on, pretty much anything wanting to touch the filesystem waits
> forever on devfs_root() for another vnode flagged as VV_ROOT and
> locked by the process holding the sx lock.
>
> Patching the devfs code with fixes from -CURRENT didn't work out.
This deadlock is fixed in current as of this:
kib 2006-09-18 13:23:08 UTC
FreeBSD src repository
Modified files:
sys/fs/devfs devfs.h devfs_devs.c devfs_vfsops.c
devfs_vnops.c
Log:
Resolve the devfs deadlock caused by LOR between devfs_mount->dm_lock and
vnode lock in devfs_allocv. Do this by temporary dropping dm_lock around
vnode locking.
For safe operation, add hold counters for both devfs_mount and devfs_dirent,
and DE_DOOMED flag for devfs_dirent. The facilities allow to continue after
dropping of the dm_lock, by making sure that referenced memory does not
disappear.
Reviewed by: tegge
Tested by: kris
Approved by: kan (mentor)
PR: kern/102335
Revision Changes Path
1.30 +11 -0 src/sys/fs/devfs/devfs.h
1.47 +12 -1 src/sys/fs/devfs/devfs_devs.c
1.51 +20 -4 src/sys/fs/devfs/devfs_vfsops.c
1.134 +70 -11 src/sys/fs/devfs/devfs_vnops.c
and
kib 2006-09-19 14:03:02 UTC
FreeBSD src repository
Modified files:
sys/fs/devfs devfs_vnops.c
Log:
Fix the bug in rev. 1.134. In devfs_allocv_drop_refs(), when not_found == 2
and drop_dm_lock is true, no unlocking shall be attempted. The lock is
already dropped and memory is freed.
Found with: Coverity Prevent(tm)
CID: 1536
Approved by: pjd (mentor)
Revision Changes Path
1.135 +1 -1 src/sys/fs/devfs/devfs_vnops.c
--
John Baldwin
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