Re: [PATCH] xfs: Fix WARN_ON(delalloc) in xfs_vm_releasepage()

Jan Kara
2013-03-19T15:42:33Z

On Tue 19-03-13 14:47:59, Dave Chinner wrote:
> On Mon, Mar 18, 2013 at 05:05:52PM +0100, Jan Kara wrote:
> > On Fri 15-03-13 15:52:14, Ben Myers wrote:
> > > Hi Jan,
> > >
> > > On Thu, Mar 14, 2013 at 02:30:54PM +0100, Jan Kara wrote:
> > > > When a dirty page is truncated from a file but reclaim gets to it before
> > > > truncate_inode_pages(), we hit WARN_ON(delalloc) in
> > > > xfs_vm_releasepage(). This is because reclaim tries to write the page,
> > > > xfs_vm_writepage() just bails out (leaving page clean) and thus reclaim
> > > > thinks it can continue and calls xfs_vm_releasepage() on page with dirty
> > > > buffers.
> > > >
> > > > Fix the issue by redirtying the page in xfs_vm_writepage(). This makes
> > > > reclaim stop reclaiming the page and also logically it keeps page in a
> > > > more consistent state where page with dirty buffers has PageDirty set.
> > >
> > > Was there an easy way to reproduce this? I'm testing and reviewing this now
> > > and it might help.
> > I used scripts/run-bash-shared-mapping.sh from the attached tarball - it
> > fires up several processes beating a file with mmap accesses while
> > truncating the file and memory stressing the machine. I presume fsx with
> > some memhog could trigger the issue as well.
>
> I have seen fsx trip this occasionally. The problem is that it was
> never reliable because of the fact that other memory pressure had to
> be generated at the same time....
>
> Is the above script something you could turn into an xfstest (I
> haven't looked at the script yet)?
Yes, that should be doable. I'll try combining fsx and usemem whether
that will be enough to trigger the race.

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR