Date: Fri, 15 Jun 2007 23:40:07 -0400 From: Kris Kennaway <kris@obsecurity.org> To: Benjamin Close <Benjamin.Close@clearchain.com> Cc: freebsd-current@freebsd.org, Kris Kennaway <kris@obsecurity.org> Subject: Re: Swapfile on ZFS & Deadlock Message-ID: <20070616034006.GA17514@rot13.obsecurity.org> In-Reply-To: <46735745.5000401@clearchain.com> References: <4672945C.3060304@clearchain.com> <20070615182521.GB9619@rot13.obsecurity.org> <46735745.5000401@clearchain.com>
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On Sat, Jun 16, 2007 at 12:51:41PM +0930, Benjamin Close wrote: > Kris Kennaway wrote: > >On Fri, Jun 15, 2007 at 11:00:04PM +0930, Benjamin Close wrote: > > > >>Hi All, > >> Whilst running out of memory compiling Xorg (scanPCI is a killer) I > >>discovered a quick way to deadlock the system: > >> > >>dd if=/dev/zero of=somefileonzfs bs=something count=something > >>mdconfig -a -f something > >>swapon /dev/md0 > >> > >>Then do something that needs swap.. instant deadlock. The system is > >>still responsive but all disk access become hung. > >> > >>Known issue? If so is there a way we can warn users/prevent users from > >>doing it? > >> > > > >Enable DEBUG_VFS_LOCKS and DEBUG_LOCKS, then break to DDB when the > >deadlock occurs and do 'show lockedvnods'. > > > Ok, enabled the above and this time got: > > swap_pager: indefinite wait buffer: bufobj: 0, blkno: 312865, size: 16384 > > just before the deadlock: > > Show locked vnods returns (hand transcribed) > > 0xffffff002c3ab5d0: tagz zfs, type VREG > usecout 1, writecount 1, refcount 2 mountedhere 0 > flags() > v_object 0xffffff002f047c80 ref 0 pages 0 > lock type zfs: EXCL (count 1) by thread 0xffffff0030573360 (pid 1188) What was needed was the backtrace that should have been also displayed here. > Pid 1188 is: > > 1188 0 0 0 SL zfs:(&zi 0xffffff000208fd58 [md0] Also a trace of the current backtrace of this. However based on the single byte of information 'i' I predict that this is due to zil (ZFS intent logging). I have turned this off on my machines because of deadlock conditions during low memory, which is also going to be true on your system. Try adding to /boot/loader.conf vfs.zfs.zil_disable=1 > called doadump and though it went through the motions, savecore didn't > find anything saved. > Not sure what you need debugging wise, let me know. > > System is Intel Core 2 duo, running in SMP amd64, updated Friday 15th June. > The box has 1G physical ram, 1G dedicated swap partition, but needs an > extra 300M to compile xf86ScanPCI.c (freaky!). Or just use -O0 on this file. Kris
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