Re: XFS related hang (was Re: How to send a break? - dump from frozen 64bit linux)

["Janos Haar" <djani22@netcenter.hu>]

----- Original Message ----- 
From: "Nathan Scott" <nathans@sgi.com>
To: "Janos Haar" <djani22@netcenter.hu>
Cc: <linux-kernel@vger.kernel.org>; <linux-xfs@oss.sgi.com>
Sent: Wednesday, May 31, 2006 6:38 AM
Subject: XFS related hang (was Re: How to send a break? - dump from frozen
64bit linux)


> On Tue, May 30, 2006 at 09:20:31PM -0400, Steven Rostedt wrote:
> > Added all those listed in the MAINTAINERS file for XFS.
>
> Thanks Steve.
>
> > On Tue, 2006-05-30 at 15:03 -0400, Valdis.Kletnieks@vt.edu wrote:
> > > On Tue, 30 May 2006 12:22:01 +0200, Janos Haar said:
> > > Half the processes on the box seem wedged at that same mutex_lock. I
can't
> > > seem to find an xfs_qm_shake in my source tree though.
>
> Its in fs/xfs/quota/xfs_qm.c.
>
> > kswapd0       D ffff81011fe03c38     0   297      1          1287    19
(L-TLB)
> > ffff81011fe03c38 0000000000000004 000000000000000a ffff81011f92ba68
> >        ffff81011f92b850 ffffffff805a23a0 0000149f99fa7d7c
000000000003bcde
> >        000000002f2c46e0 ffff81008bc37180
> > Call Trace: <ffffffff804e5522>{schedule_timeout+34}
> >        <ffffffff80269f87>{xfs_qm_dqunpin_wait+220}
<ffffffff80140e74>{debug_mutex_free_waiter+141}
>
> So, we're waiting here on a synchronisation variable that'll
> be released once the dquot metadata buffer write completes.
>
> > So it is now waiting to be woken up by something that calls:
> >
> > xfs_qm_dquot_logitem_unpin  which seems to be the function to wake it
> > up.
>
> Mhmm, that'd be called by the I/O completion handler on the buffer
> containing that dquot.
>
> > And decyphering all the macro crap it seems that the function that wakes
> > it up is xfs_trans_chunk_committed, or xfs_trans_uncommit.
>
> Right (the former, at this point in the code).
>
> > The above xfs_qm_dqunpin_wait still looks awfully racy, and the
> > xfs_log_force, which I'm assuming wakes up whoever is suppose to wake up
> > kswapd0, doesn't have a return code check.  So if it failed to do
>
> The logforce isn't race-critical here - its ensuring writeout
> of previously logged buffers is started before we go to sleep
> waiting for the driver to wake us up when its done.
>
> An earlier I/O error on the journal is the only thing the log
> force can return as an error there, which isnt useful at that
> point anyway (we're in a kernel thread trying to free mem).
>
> > whatever the hell it's doing (that code gives me a headache), it looks
>
> Heh, likewise.  I have voodoo dolls of one or two of the early
> XFS folks that I like to poke with needles occasionally.. :)
>
> > like this guy might sleep forever holding a lock that will prevent
> > others from freeing kernel memory.
>
> It will sleep until the previously initiated buffer write is done.
> AFAICT, we aren't seeing the I/O completion here for some reason...
> which points more to a possible device driver or h/ware issue (that
> is the usual root cause of this sort of hang, anyway).
>
> cheers.

Hey, i think i found something.
My quota on my huge device is broken.
(inferno   -- 18014398504855404       0       0        18446744073709551519
0     0)
I cant found a way to re-initialize it.
But anyway, at this point i dont need it, trying to disable the quota usage.
We will see....

Thanks a lot!

Janos

>
> -- 
> Nathan
> -
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