nfsd hung on ufs vnode lock
jjh at deterlab.net
Mon Jan 31 22:29:25 UTC 2011
On Mon, Jan 31, 2011 at 12:00:29PM -0500, John Baldwin wrote:
> On Friday, January 28, 2011 8:10:41 pm John Hickey wrote:
> > There was a previous thread about this, but it doesn't look like there was any resolution:
> > http://lists.freebsd.org/pipermail/freebsd-stable/2010-May/056986.html
> > I run a fileserver for an Emulab (www.emulab.net) system. As such, the exports table is constantly modified as experiments are swapped in and
> out. We also get a lot of researchers using NFS for strange things. In this case, the exclusive lock was for a cache directory shared by about
> 36 machines running Ubuntu 8.04 and mounting with NFSv2. Eventually, all our nfsd processes get stuck since the exclusive lock for the directory
> is never released. I could use any and all pointers on getting this fixed.
> > What I am running:
> > jjh at users: ~$ uname -a
> > FreeBSD users.isi.deterlab.net 7.3-RELEASE-p2 FreeBSD 7.3-RELEASE-p2 #9: Tue Sep 14 16:24:57 PDT 2010
> root at users.isi.deterlab.net:/usr/obj/usr/src/sys/USERS7 i386
> > Here are the sleepchains for my system (note that 0xd1f72678 appears twice):
> > 0xce089cf0: tag syncer, type VNON
> > usecount 1, writecount 0, refcount 2 mountedhere 0
> > flags ()
> > lock type syncer: EXCL (count 1) by thread 0xcdb4b000 (pid 46)
> > 0xd1f72678: tag ufs, type VDIR
> > usecount 2, writecount 0, refcount 67 mountedhere 0
> > flags ()
> > v_object 0xd1e90e80 ref 0 pages 1
> > lock type ufs: EXCL (count 1) by thread 0xce1146c0 (pid 866) with 62 pending
> > ino 143173560, on dev mfid0s1f
> From the stack trace, this vnode is the directory vnode that is the parent
> of the new file being created.
> > (kgdb) bt
> > #0 sched_switch (td=0xce1146c0, newtd=Variable "newtd" is not available.
> > ) at /usr/src/sys/kern/sched_ule.c:1936
> > #1 0xc080a4a6 in mi_switch (flags=Variable "flags" is not available.
> > ) at /usr/src/sys/kern/kern_synch.c:444
> > #2 0xc0837aab in sleepq_switch (wchan=Variable "wchan" is not available.
> > ) at /usr/src/sys/kern/subr_sleepqueue.c:497
> > #3 0xc08380f6 in sleepq_wait (wchan=0xd4176394) at /usr/src/sys/kern/subr_sleepqueue.c:580
> > #4 0xc080a92a in _sleep (ident=0xd4176394, lock=0xc0ceb498, priority=80, wmesg=0xc0bb656e "ufs", timo=0) at /usr/src/sys/kern/kern_synch.c:230
> > #5 0xc07ea9fa in acquire (lkpp=0xcd7375a0, extflags=Variable "extflags" is not available.
> > ) at /usr/src/sys/kern/kern_lock.c:151
> > #6 0xc07eb2ec in _lockmgr (lkp=0xd4176394, flags=8194, interlkp=0xd41763c4, td=0xce1146c0, file=0xc0bc20c8 "/usr/src/sys/kern/vfs_subr.c",
> > at /usr/src/sys/kern/kern_lock.c:384
> > #7 0xc0a24765 in ffs_lock (ap=0xcd737608) at /usr/src/sys/ufs/ffs/ffs_vnops.c:377
> > #8 0xc0b26876 in VOP_LOCK1_APV (vop=0xc0ca4740, a=0xcd737608) at vnode_if.c:1618
> > #9 0xc0896d76 in _vn_lock (vp=0xd417633c, flags=8194, td=0xce1146c0, file=0xc0bc20c8 "/usr/src/sys/kern/vfs_subr.c", line=2062) at
> Note that, this vnode (vp) doesn't show up in your list above. You can try
> using my gdb scripts at www.freebsd.org/~jhb/gdb (you want gdb6* and do
> 'source gdb6'). You can then do 'vprint vp' at this frame and should see
> lock details about who holds this lock. However, I would not expect the
> vnode lock for a new i-node to be already held.
jjh at users: ~$ kgdb /boot/kernel/kernel vmcore.0
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This GDB was configured as "i386-marcel-freebsd"...
Unread portion of the kernel message buffer:
cpuid = 1
Physical memory: 3566 MB
Dumping 437 MB: 422 406 390 374 358 342 326 310 294 278 262 246 230 214 198 182 166 150 134 118 102 86 70 54 38 22 6
#0 doadump () at pcpu.h:196
196 pcpu.h: No such file or directory.
(kgdb) source gdb6
(kgdb) proc 866
[Switching to thread 66 (Thread 100104)]#0 sched_switch (td=0xce1146c0, newtd=Variable "newtd" is not available.
) at /usr/src/sys/kern/sched_ule.c:1936
1936 cpuid = PCPU_GET(cpuid);
(kgdb) frame 9
#9 0xc0896d76 in _vn_lock (vp=0xd417633c, flags=8194, td=0xce1146c0, file=0xc0bc20c8 "/usr/src/sys/kern/vfs_subr.c", line=2062) at vnode_if.h:851
warning: Source file is more recent than executable.
851 return (VOP_LOCK1_APV(vp->v_op, &a));
(kgdb) vprint vp
0xd417633c: tag none, type VBAD
usecount 0, writecount 0, refcount 1 mountedhere 0x0
lock type ufs: UNLOCKED with 1 pending
> There's a chance though you are tripping over the bug fixed by these two
I should be able to sync up with 7.4 without much pain in a few days.
> Author: jhb
> Date: Fri Jul 16 20:23:24 2010
> New Revision: 210173
> URL: http://svn.freebsd.org/changeset/base/210173
> When the MNTK_EXTENDED_SHARED mount option was added, some filesystems were
> changed to defer the setting of VN_LOCK_ASHARE() (which clears LK_NOSHARE
> in the vnode lock's flags) until after they had determined if the vnode was
> a FIFO. This occurs after the vnode has been inserted into a VFS hash or
> some similar table, so it is possible for another thread to find this vnode
> via vget() on an i-node number and block on the vnode lock. If the lockmgr
> interlock (vnode interlock for vnode locks) is not held when clearing the
> LK_NOSHARE flag, then the lk_flags field can be clobbered. As a result
> the thread blocked on the vnode lock may never get woken up. Fix this by
> holding the vnode interlock while modifying the lock flags in this case.
> The softupdates code also toggles LK_NOSHARE in one function to close a
> race with snapshots. Fix this code to grab the interlock while fiddling
> with lk_flags.
> Author: jhb
> Date: Fri Aug 20 20:58:57 2010
> New Revision: 211533
> URL: http://svn.freebsd.org/changeset/base/211533
> Revert 210173 as it did not properly fix the bug. It assumed that the
> VI_LOCK() for a given vnode was used as the internal interlock for that
> vnode's v_lock lockmgr lock. This is not the case. Instead, add dedicated
> routines to toggle the LK_NOSHARE and LK_CANRECURSE flags. These routines
> lock the lockmgr lock's internal interlock to synchronize the updates to
> the flags member with other threads attempting to acquire the lock. The
> VN_LOCK_A*() macros now invoke these routines, and the softupdates code
> uses these routines to temporarly enable recursion on buffer locks.
> Reviewed by: kib
> John Baldwin
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