From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
"xfs@oss.sgi.com" <xfs@oss.sgi.com>,
Stefan Priebe - Profihost AG <s.priebe@profihost.ag>
Subject: Re: [xfs-masters] xfs deadlock in stable kernel 3.0.4
Date: Thu, 22 Sep 2011 18:01:51 -0400 [thread overview]
Message-ID: <20110922220151.GA21701@infradead.org> (raw)
In-Reply-To: <20110922214956.GX15688@dastard>
On Fri, Sep 23, 2011 at 07:49:56AM +1000, Dave Chinner wrote:
> On Thu, Sep 22, 2011 at 10:14:57AM -0400, Christoph Hellwig wrote:
> > By default, a wq guarantees non-reentrance only on the same
> > CPU. A work item may not be executed concurrently on the same
> > CPU by multiple workers but is allowed to be executed
> > concurrently on multiple CPUs. This flag makes sure
> > non-reentrance is enforced across all CPUs. Work items queued
> > to a non-reentrant wq are guaranteed to be executed by at most
> > one worker system-wide at any given time.
> >
> > So this still seems to preferable for the ail workqueue, and should be
> > able to replace the XFS_AIL_PUSHING_BIT protections.
>
> No, we can't. WQ_NON_REENTRANT only protects against concurrency on
> the same CPU, not across all CPUs - it still allows concurrent
> per-CPU work processing on the same work item.
Non concurrently for a given work_struct on the same CPU is the default,
WQ_NON_REENTRANT extents that to not beeing exectuted concurrently at
all. Check the documentation above again, or the code - just look
for the only occurance of WQ_NON_REENTRANT in kernel/workqueue.c and
the surronuding code (e.g. find_worker_executing_work and the
current_work field in struct worker)
> However, we want only a *single* AIL worker instance executing per
> filesystem, not per-cpu per filesystem. Concurrent per-filesystem
> workers will simply bash on the AIL lock trying to walk the AIL at
> the same time, and this is precisely the issue the single AIL worker
> setup is avoiding. The XFS_AIL_PUSHING_BIT is what enforces the
> single per-filesystem push worker running at any time.
I think that's exactly what WQ_NON_REENTRANT is intended for.
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next prev parent reply other threads:[~2011-09-22 22:01 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-10 12:23 xfs deadlock in stable kernel 3.0.4 Stefan Priebe
2011-09-12 15:21 ` Christoph Hellwig
2011-09-12 16:46 ` Stefan Priebe
2011-09-12 20:05 ` Christoph Hellwig
2011-09-13 6:04 ` Stefan Priebe - Profihost AG
2011-09-13 19:31 ` Stefan Priebe - Profihost AG
2011-09-13 20:50 ` Christoph Hellwig
2011-09-13 21:52 ` [xfs-masters] " Alex Elder
2011-09-13 21:58 ` Alex Elder
2011-09-13 22:26 ` Christoph Hellwig
2011-09-14 7:26 ` Stefan Priebe - Profihost AG
2011-09-14 7:48 ` Stefan Priebe - Profihost AG
2011-09-14 8:49 ` Stefan Priebe - Profihost AG
2011-09-14 14:30 ` Christoph Hellwig
2011-09-14 14:30 ` Christoph Hellwig
2011-09-14 16:06 ` Stefan Priebe - Profihost AG
2011-09-18 9:14 ` Stefan Priebe - Profihost AG
2011-09-18 20:04 ` Christoph Hellwig
2011-09-19 10:54 ` Stefan Priebe - Profihost AG
2011-09-18 23:02 ` Dave Chinner
2011-09-20 0:47 ` Stefan Priebe
2011-09-20 1:01 ` Stefan Priebe
2011-09-20 10:09 ` Stefan Priebe - Profihost AG
2011-09-20 16:02 ` Christoph Hellwig
2011-09-20 17:23 ` Stefan Priebe - Profihost AG
2011-09-20 17:24 ` Christoph Hellwig
2011-09-20 17:35 ` Stefan Priebe - Profihost AG
2011-09-20 22:30 ` Christoph Hellwig
2011-09-21 2:11 ` [xfs-masters] " Dave Chinner
2011-09-21 7:40 ` Stefan Priebe - Profihost AG
2011-09-21 11:42 ` Dave Chinner
2011-09-21 11:55 ` Stefan Priebe - Profihost AG
2011-09-21 12:26 ` Christoph Hellwig
2011-09-21 13:42 ` Stefan Priebe
2011-09-21 16:48 ` Stefan Priebe - Profihost AG
2011-09-21 17:26 ` Stefan Priebe - Profihost AG
2011-09-21 19:01 ` Stefan Priebe - Profihost AG
2011-09-21 23:07 ` Dave Chinner
2011-09-22 14:14 ` Christoph Hellwig
2011-09-22 21:49 ` Dave Chinner
2011-09-22 22:01 ` Christoph Hellwig [this message]
2011-09-23 5:28 ` Stefan Priebe - Profihost AG
2011-09-22 0:53 ` Dave Chinner
2011-09-22 5:27 ` Stefan Priebe - Profihost AG
2011-09-22 7:52 ` Stefan Priebe - Profihost AG
2011-09-21 7:36 ` Stefan Priebe - Profihost AG
2011-09-21 11:39 ` Christoph Hellwig
2011-09-21 13:39 ` Stefan Priebe
2011-09-21 14:17 ` Christoph Hellwig
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