Re: [PATCH] writeback: Fix data corruption on NFS

[Fengguang Wu <fengguang.wu@intel.com>]

On Mon, Jan 13, 2014 at 11:58:26AM +0100, Jan Kara wrote:
> On Sat 14-12-13 13:45:39, Wu Fengguang wrote:
> > On Wed, Dec 11, 2013 at 08:59:36PM +0100, Jan Kara wrote:
> > > Commit 4f8ad655dbc8 "writeback: Refactor writeback_single_inode()" added
> > > a condition to skip clean inode. However this is wrong in WB_SYNC_ALL
> > > mode because there we also want to wait for outstanding writeback on
> > > possibly clean inode. This was causing occasional data corruption issues
> > > on NFS because it uses sync_inode() to make sure all outstanding writes
> > > are flushed to the server before truncating the inode and with
> > > sync_inode() returning prematurely file was sometimes extended back
> > > by an outstanding write after it was truncated.
> > > 
> > > So modify the test to also check for pages under writeback in
> > > WB_SYNC_ALL mode.
> > 
> > Applied to the writeback tree. Thank you, Jan!
>   Didn't you forget to send pull request? I don't see the patch in mainline
> yet and since this is a data corruption issue, it would be nice to get it
> out for 3.13...

Sorry I scheduled it for the next release.. However you are right that
it should have been merged earlier. I should have speak out the plan
so that we realize and resolve the different opinions earlier.

I'll try to send a pull request to Linus and hope he still accepts
patches.

Fengguang

> > > CC: stable@vger.kernel.org # >= 3.5
> > > Fixes: 4f8ad655dbc82cf05d2edc11e66b78a42d38bf93
> > > Reported-and-tested-by: Dan Duval <dan.duval@oracle.com>
> > > Signed-off-by: Jan Kara <jack@suse.cz>
> > > ---
> > >  fs/fs-writeback.c | 15 +++++++++------
> > >  1 file changed, 9 insertions(+), 6 deletions(-)
> > > 
> > >  Fenguang, can you please merge this patch? Thanks!
> > > 
> > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> > > index 1f4a10ece2f1..e0259a163f98 100644
> > > --- a/fs/fs-writeback.c
> > > +++ b/fs/fs-writeback.c
> > > @@ -516,13 +516,16 @@ writeback_single_inode(struct inode *inode, struct bdi_writeback *wb,
> > >  	}
> > >  	WARN_ON(inode->i_state & I_SYNC);
> > >  	/*
> > > -	 * Skip inode if it is clean. We don't want to mess with writeback
> > > -	 * lists in this function since flusher thread may be doing for example
> > > -	 * sync in parallel and if we move the inode, it could get skipped. So
> > > -	 * here we make sure inode is on some writeback list and leave it there
> > > -	 * unless we have completely cleaned the inode.
> > > +	 * Skip inode if it is clean and we have no outstanding writeback in
> > > +	 * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
> > > +	 * function since flusher thread may be doing for example sync in
> > > +	 * parallel and if we move the inode, it could get skipped. So here we
> > > +	 * make sure inode is on some writeback list and leave it there unless
> > > +	 * we have completely cleaned the inode.
> > >  	 */
> > > -	if (!(inode->i_state & I_DIRTY))
> > > +	if (!(inode->i_state & I_DIRTY) &&
> > > +	    (wbc->sync_mode != WB_SYNC_ALL ||
> > > +	     !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
> > >  		goto out;
> > >  	inode->i_state |= I_SYNC;
> > >  	spin_unlock(&inode->i_lock);
> > > -- 
> > > 1.8.1.4
> -- 
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR