From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
viro@ZenIV.linux.org.uk, josef@redhat.com, jeffmerkey@gmail.com
Subject: Re: [PATCH 2/5] fsfreeze: emergency thaw will deadlock on s_umount
Date: Mon, 21 Jun 2010 03:47:56 -0400 [thread overview]
Message-ID: <20100621074756.GA2201@infradead.org> (raw)
In-Reply-To: <20100621015731.GJ6590@dastard>
On Mon, Jun 21, 2010 at 11:57:31AM +1000, Dave Chinner wrote:
> This patch doesn't try to deal with the bdev/super mismatches; all
> it does is prevent an obvious deadlock. Calling freeze/thaw_super
> directly will serialise on the s_umount lock, calling
> freeze/thaw_bdev() will serialise on the bdev freeze mutex, and if
> we mix the two they'll serialise on the s_umount lock. So I think
> with this patch serialisation will still occur correctly but avoid
> the current deadlock.
>
> I'll change the commit message to explain this better.
I don;t think the explanation alone is enough.
Right now thaw_super itself is only serialized by exclusive shared
s_umount. thaw_bdev it also serialized by bd_fsfreeze_mutex, but
there are callers of thaw_super that do not go through thaw_bdev, so
our locking is not enough here.
next prev parent reply other threads:[~2010-06-21 7:47 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-10 7:19 [RFC, PATCH 0/5] fsfreeze: fix sb vs bdev freeze/thaw b0rkage Dave Chinner
2010-06-10 7:19 ` [PATCH 1/5] fsfreeze: Prevent emergency thaw from looping infinitely Dave Chinner
2010-06-14 15:18 ` Christoph Hellwig
2010-06-14 23:19 ` Dave Chinner
2010-06-10 7:19 ` [PATCH 2/5] fsfreeze: emergency thaw will deadlock on s_umount Dave Chinner
2010-06-14 15:20 ` Christoph Hellwig
2010-06-14 23:21 ` Dave Chinner
2010-06-21 1:57 ` Dave Chinner
2010-06-21 7:47 ` Christoph Hellwig [this message]
2010-06-10 7:19 ` [PATCH 3/5] fsfreeze: freeze_super and thaw_bdev don't play well together Dave Chinner
2010-06-14 15:22 ` Christoph Hellwig
2010-06-15 0:01 ` Dave Chinner
2010-06-15 6:24 ` Christoph Hellwig
2010-06-10 7:19 ` [PATCH 4/5] fsfreeze: switch to using super methods everywhere Dave Chinner
2010-06-14 15:23 ` Christoph Hellwig
2010-06-10 7:19 ` [PATCH 5/5] fsfreeze: move emergency thaw code to fs/super.c Dave Chinner
2010-06-14 15:25 ` Christoph Hellwig
2010-06-10 12:45 ` [RFC, PATCH 0/5] fsfreeze: fix sb vs bdev freeze/thaw b0rkage Josef Bacik
2010-06-10 12:45 ` Josef Bacik
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