From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Brian Foster <bfoster@redhat.com>,
xfs@oss.sgi.com
Subject: Re: [PATCH v2] xfs: re-enable xfsaild idle mode and fix associated races
Date: Thu, 21 Jun 2012 03:11:36 -0400 [thread overview]
Message-ID: <20120621071135.GA5106@infradead.org> (raw)
In-Reply-To: <20120620223548.GK30705@dastard>
On Thu, Jun 21, 2012 at 08:35:48AM +1000, Dave Chinner wrote:
> writes are single instructions on 64 bit systems. The lock is
> required for 32 bit systems because the write requires separate 32
> bit writes to the LSN which can result in unlocked accesses seeing
> partially updated (and hence incorrect) LSN values.
>
> So the memory barriers are definitely needed for 64 bit machines
> because there is no locking on the update and spinlocks only provide
> memory barriers via unlock->lock transitions, not via a single
> spin_lock() call.
Indeed. So we'll either need the barriers, or just always take xa_lock
in xfs_ail_push. Given that xa_lock and xa_target appear in the same
cache line it probably wouldn't even make much of a difference.
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prev parent reply other threads:[~2012-06-21 7:11 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-07 16:49 [PATCH v2] xfs: re-enable xfsaild idle mode and fix associated races Brian Foster
2012-06-20 8:05 ` Christoph Hellwig
2012-06-20 15:35 ` Brian Foster
2012-06-20 15:59 ` Brian Foster
2012-06-20 22:35 ` Dave Chinner
2012-06-21 7:11 ` Christoph Hellwig [this message]
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