Re: [PATCH] xfs: fix race while discarding buffers [V4]

Ben Myers
2012-08-24T18:43:57Z

Carlos and Dave,

On Tue, Aug 21, 2012 at 09:21:10AM +1000, Dave Chinner wrote:
> On Mon, Aug 20, 2012 at 07:47:51PM -0300, Carlos Maiolino wrote:
> > Thanks for the comments.
> > >
> > > What was the symptom that led to the discovery of this problem?
> > >
> > > Reviewed-by: Ben Myers <bpm@sgi.com>
> > >
> >
> > It started with the messages like the example below being logged by syslog:
> >
> > shrink_slab: xfs_buftarg_shrink+0x0/0x160 [xfs] negative objects to delete nr=-61993820
> > shrink_slab: xfs_buftarg_shrink+0x0/0x160 [xfs] negative objects to delete nr=-146
> > shrink_slab: xfs_buftarg_shrink+0x0/0x160 [xfs] negative objects to delete nr=-240601220
> > shrink_slab: xfs_buftarg_shrink+0x0/0x160 [xfs] negative objects to delete nr=-152
> > shrink_slab: xfs_buftarg_shrink+0x0/0x160 [xfs] negative objects to delete nr=-2921236993
> >
> > These messages came from shrink_slab().
>
> Worth noting is that this warning came from a RHEL kernel, not a
> mainline kernel. The mainline kernels don't screw up the nr_to_scan
> calculations when a negative object count is returned to them.
> Hence mainline kernels are not impacted by the accounting bug at
> all...

Thanks for the additional information. Sometimes it is helpful to know the
symptom along with the fix.

Regards,
Ben