6-STABLE snapshot (background fsck) lock-up

[Kostik Belousov]

On Mon, Aug 21, 2006 at 12:27:53PM -0400, John Baldwin wrote:
> On Thursday 17 August 2006 08:30, Eric Anderson wrote:
> > On 08/17/06 07:25, Kostik Belousov wrote:
> > > On Thu, Aug 17, 2006 at 07:08:31AM -0500, Eric Anderson wrote:
> > >> I've seen this several times now, but this time I got a dump. 
> > >> Basically, the system comes up after unclean shutdown, throws a bunch of 
> > >> filesystems into the background fsck list, and begins 60 seconds later. 
> > >>    After some amount of time, the system will lock up, presumably hung 
> > >> waiting on locks.
> > >>
> > >> Here's some info:
> > >> lock type bufwait: EXCL (count 1) by thread 0xffffff0128812980 (pid 804) 
> > >> lock type getblk: EXCL (count 1) by thread 0xffffff0128812980 (pid 
> > >> 804)Locked vnodes
> > >>
> > >> 0xffffff01c5c9f000: tag ufs, type VREG
> > >>     usecount 1, writecount 0, refcount 13656 mountedhere 0
> > >>     flags (VV_SYSTEM)
> > >>     v_object 0xffffff01b09542a0 ref 0 pages 1691637
> > >>      lock type snaplk: EXCL (count 1) by thread 0xffffff0128812980 (pid 
> > >> 804)
> > >>         ino 4, on dev label/vol4
> > >>
> > >>
> > >>
> > >> How can I use kgdb to get more debugging information from this?
> > >>
> > > Look at the
> > > 
> http://www.freebsd.org/doc/en_US.ISO8859-1/books/developers-handbook/kerneldebug-deadlocks.html
> > > for instructions for ddb.
> > > 
> > > What is the date of the system checkout ?
> > 
> > 
> > 6-STABLE from ~8/12/06.
> > 
> > So there's not much that can be done with the vmcore?
> 
> Actually, there is stuff that can be done with the vmcore.  Download 
> http://www.FreeBSD.org/~jhb/gdb.6
> 
> Then in kgdb do:
> 
> (gdb) source /path/to/6.gdb
> (gdb) sleepchain 0xffffff0128812980
> 
> And see if that spits out a cycle.

In fact, I just committed the fix that shall help with snapshots on AMD64.
Please, try sys/ufs/ffs/ffs_snapshot.c, rev. 1.128.
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