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Re: [PATCH 4/4] xfs: Protect xfs_file_aio_write() with sb_start_write -

To: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 4/4] xfs: Protect xfs_file_aio_write() with sb_start_write - sb_end_write
From: Jan Kara <jack@xxxxxxx>
Date: Thu, 12 Jan 2012 22:36:56 +0100
Cc: Jan Kara <jack@xxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Eric Sandeen <sandeen@xxxxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>, Surbhi Palande <csurbhi@xxxxxxxxx>, Kamal Mostafa <kamal@xxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Ben Myers <bpm@xxxxxxx>, Alex Elder <elder@xxxxxxxxxx>
In-reply-to: <20120112212941.GI23916@xxxxxxxxxxxxxxxxxx>
References: <1326331253-6497-1-git-send-email-jack@xxxxxxx> <1326331253-6497-5-git-send-email-jack@xxxxxxx> <20120112212941.GI23916@xxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
On Thu 12-01-12 21:29:41, Al Viro wrote:
> On Thu, Jan 12, 2012 at 02:20:53AM +0100, Jan Kara wrote:
> > Replace racy xfs_wait_for_freeze() check with reliable sb_start_write()
> > - sb_end_write() locking. Due to lock ranking dictated by the page fault
> > code we have to call sb_start_write() after we acquire ilock.
> > 
> > CC: Ben Myers <bpm@xxxxxxx>
> > CC: Alex Elder <elder@xxxxxxxxxx>
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > ---
> >  fs/xfs/xfs_file.c |    6 ++++--
> >  1 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> > index 753ed9b..c5f879b 100644
> > --- a/fs/xfs/xfs_file.c
> > +++ b/fs/xfs/xfs_file.c
> > @@ -862,9 +862,11 @@ xfs_file_dio_aio_write(
> >             *iolock = XFS_IOLOCK_SHARED;
> >     }
> >  
> > +   sb_start_write(inode->i_sb);
> >     trace_xfs_file_direct_write(ip, count, iocb->ki_pos, 0);
> >     ret = generic_file_direct_write(iocb, iovp,
> >                     &nr_segs, pos, &iocb->ki_pos, count, ocount);
> > +   sb_end_write(inode->i_sb);
> 
> What lock ordering do you have in mind?  Explicit description in fs/super.c,
> please...
  Good point. Will add explanatory comment. Thanks.

                                                                Honza
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR

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