linux-kernel - Re: [git pull] vfs.git fixes for -rc2

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Message-ID: <20140210104747.GV13997@dastard>
Date:	Mon, 10 Feb 2014 21:47:47 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [git pull] vfs.git fixes for -rc2

On Sun, Feb 09, 2014 at 11:36:43PM +0000, Al Viro wrote:
> 	A couple of fixes, both -stable fodder.  O_SYNC bug is
> fairly old...  Please, pull from the usual place -
> git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git for-linus
> 
> Shortlog:
> Al Viro (2):
>       fix O_SYNC|O_APPEND syncing the wrong range on write()

As i pointed out in a private thread this doesn't fix XFS. It passes
a private "pos" variable to generic_write_checks() and so
iocb->ki_pos never gets updated to point at the new EOF when
O_APPEND is set. Hence the code inthe above commit is still syncing
the wrong range.

Indeed, I think that __generic_file_aio_write has the same problem.
It gets called from generic_file_aio_write() like so:

	ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);

And __generic_file_aio_write() does this:

	pos = *ppos;
	....
	err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));

and the updated pos value on O_APPEND writes is never folded back
into ppos. Hence the later call to generic_write_sync() still has
the wrong range....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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