From: Dave Chinner <david@fromorbit.com>
Subject: Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict_inode()
Date: Fri, 26 Aug 2011 18:44:03 +1000
Message-ID: <20110826084403.GA3162@dastard>
References: <E1QwnAu-00087H-8X@tytso-glaptop.cam.corp.google.com>
 <20110826073507.GZ3162@dastard>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Jiaying Zhang <jiayingz@google.com>, linux-ext4@vger.kernel.org
To: Theodore Ts'o <tytso@mit.edu>
Content-Disposition: inline
In-Reply-To: <20110826073507.GZ3162@dastard>
Sender: linux-ext4-owner@vger.kernel.org

On Fri, Aug 26, 2011 at 05:35:07PM +1000, Dave Chinner wrote:
> On Thu, Aug 25, 2011 at 11:33:44PM -0400, Theodore Ts'o wrote:
> > 
> > Note: this will probably need to be sent to Linus as an emergency
> > bugfix ASAP, since it was introduced in 3.1-rc1, so it represents a
> > regression.
> 
> It doesn't appear to be a bug. All of the new ext4 lockdep reports
> in 3.1 I've seen (except for the mmap_sem/i_mutex one) are false
> positives....

While the lockdep report is false positive, I agree that your
change is the right fix to make - the IO completions are already
queued on the workqueue, so they don't need to be flushed to get
them to complete. All that needs to be done is call
ext4_ioend_wait() for them to complete, and that gets rid of the
i_mutex altogether. (*)

Sorry for the noise, Ted.

Cheers,

Dave.

(*) Even better would be to get rid of that flush list altogether
and just use ext4_ioend_wait() everywhere....
-- 
Dave Chinner
david@fromorbit.com