linux-ext4 - Re: [patch, resend] ext4: fix race between unwritten extent conversion and truncate

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Message-ID: <20120221040007.GE25249@thunk.org>
Date:	Mon, 20 Feb 2012 23:00:07 -0500
From:	Ted Ts'o <tytso@....edu>
To:	Jeff Moyer <jmoyer@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [patch, resend] ext4: fix race between unwritten extent
 conversion and truncate

On Thu, Feb 16, 2012 at 03:26:48PM -0500, Jeff Moyer wrote:
> Hi,
> 
> The following comment in ext4_end_io_dio caught my attention:
> 
> 	/* XXX: probably should move into the real I/O completion handler */
>         inode_dio_done(inode);
> 
> The truncate code takes i_mutex, then calls inode_dio_wait.  Because the
> ext4 code path above will end up dropping the mutex before it is
> reacquired by the worker thread that does the extent conversion, it
> seems to me that the truncate can happen out of order.  Jan Kara
> mentioned that this might result in error messages in the system logs,
> but that should be the extent of the "damage."
> 
> The fix is pretty straight-forward: don't call inode_dio_done until the
> extent conversion is complete.
> 
> Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
> Reviewed-by: Jan Kara <jack@...e.cz>

Thanks, applied.

						- Ted
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