Re: [PATCH 1/3] xfs: fix up quotacheck buffer list error handling

[Brian Foster <bfoster@redhat.com>]

On Thu, Apr 06, 2017 at 03:39:21PM -0700, Darrick J. Wong wrote:
> On Fri, Feb 24, 2017 at 02:53:19PM -0500, Brian Foster wrote:
> > The quotacheck error handling of the delwri buffer list assumes the
> > resident buffers are locked and doesn't clear the _XBF_DELWRI_Q flag
> > on the buffers that are dequeued. This can lead to assert failures
> > on buffer release and possibly other locking problems.
> > 
> > Update the error handling code to lock each buffer as it is removed
> > from the buffer list and clear the delwri queue flag.
> > 
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ---
> >  fs/xfs/xfs_buf.c | 2 ++
> >  fs/xfs/xfs_qm.c  | 2 ++
> >  2 files changed, 4 insertions(+)
> > 
> > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > index ac3b4db..e566510 100644
> > --- a/fs/xfs/xfs_buf.c
> > +++ b/fs/xfs/xfs_buf.c
> > @@ -1078,6 +1078,8 @@ void
> >  xfs_buf_unlock(
> >  	struct xfs_buf		*bp)
> >  {
> > +	ASSERT(xfs_buf_islocked(bp));
> > +
> >  	XB_CLEAR_OWNER(bp);
> >  	up(&bp->b_sema);
> >  
> > diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
> > index b669b12..4ff993c 100644
> > --- a/fs/xfs/xfs_qm.c
> > +++ b/fs/xfs/xfs_qm.c
> > @@ -1387,6 +1387,8 @@ xfs_qm_quotacheck(
> >  	while (!list_empty(&buffer_list)) {
> >  		struct xfs_buf *bp =
> >  			list_first_entry(&buffer_list, struct xfs_buf, b_list);
> > +		xfs_buf_lock(bp);
> > +		bp->b_flags &= ~_XBF_DELWRI_Q;
> >  		list_del_init(&bp->b_list);
> >  		xfs_buf_relse(bp);
> 
> Hmm, was this the only place we ever _buf_unlock'd an unlocked buffer?
> 

I'm not aware of any other places (otherwise I would try to fix them :).
Or perhaps I'm not following the question...

I do recall a similar problem with flush locks fixed in commit 98efe8a
("xfs: fix unbalanced inode reclaim flush locking").

Brian

> --D
> 
> >  	}
> > -- 
> > 2.7.4
> > 
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