Date: Sat, 16 Jun 2007 12:51:41 +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: <46735745.5000401@clearchain.com> In-Reply-To: <20070615182521.GB9619@rot13.obsecurity.org> References: <4672945C.3060304@clearchain.com> <20070615182521.GB9619@rot13.obsecurity.org>
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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.
Cheers,
Benjamin
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