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

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Message-ID: <x4962fyyxij.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 26 Jan 2012 16:17:08 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Jan Kara <jack@...e.cz>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [patch] ext4: fix race between unwritten extent conversion and truncate

Jan Kara <jack@...e.cz> writes:

> On Thu 26-01-12 15:59:11, 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 extra journal I/O, which isn't nice,
>   Funny misunderstanding ;) I meant we will complain to system log with error
> messages / WARN_ON.

Heh.  Ted, let me know if I need to repost to fix that up...

Cheers,
Jeff
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