Date: Sat, 16 Jun 2007 12:53:45 +0930 From: Benjamin Close <Benjamin.Close@clearchain.com> To: Kris Kennaway <kris@obsecurity.org> Cc: freebsd-current@freebsd.org Subject: Re: Swapfile on ZFS & Deadlock Message-ID: <467357C1.9020903@clearchain.com> 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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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)
>
> Pid 1188 is:
>
> 1188 0 0 0 SL zfs:(&zi 0xffffff000208fd58 [md0]
>
> 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!).
> Figured a temp solution would be to allocate a 500M swap file on /var
> which is zfs.
Forgot to mention, this happens regardless of the state of
vfs.zfs.prefetch_disable and there was ~200M swap free (in the swapfile,
none in the partition) when it deadlocked.
Cheers,
Benjamin
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