Re: [PATCH] ceph: cancel delayed work instead of flushing on mdsc teardown

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2021-07-29 at 10:56 +0800, Xiubo Li wrote:
> On 7/28/21 4:12 AM, Jeff Layton wrote:
> > The first thing metric_delayed_work does is check mdsc->stopping,
> > and then return immediately if it's set...which is good since we would
> > have already torn down the metric structures at this point, otherwise.
> > 
> > Worse yet, it's possible that the ceph_metric_destroy call could race
> > with the delayed_work, in which case we could end up a end up accessing
> > destroyed percpu variables.
> > 
> > At this point in the mdsc teardown, the "stopping" flag has already been
> > set, so there's no benefit to flushing the work. Just cancel it instead,
> > and do so before we tear down the metrics structures.
> > 
> > Cc: Xiubo Li <xiubli@redhat.com>
> > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > ---
> >   fs/ceph/mds_client.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
> > index c43091a30ba8..d3f2baf3c352 100644
> > --- a/fs/ceph/mds_client.c
> > +++ b/fs/ceph/mds_client.c
> > @@ -4977,9 +4977,9 @@ void ceph_mdsc_destroy(struct ceph_fs_client *fsc)
> >   
> >   	ceph_mdsc_stop(mdsc);
> >   
> > +	cancel_delayed_work_sync(&mdsc->metric.delayed_work);
> >   	ceph_metric_destroy(&mdsc->metric);
> >   
> 
> In the "ceph_metric_destroy()" it will also do 
> "cancel_delayed_work_sync(&mdsc->metric.delayed_work)".
> 
> We can just move the it to the front of the _destory().
> 
> 

Good point! I'll send a v2 after I test it out.

> 
> > -	flush_delayed_work(&mdsc->metric.delayed_work);
> >   	fsc->mdsc = NULL;
> >   	kfree(mdsc);
> >   	dout("mdsc_destroy %p done\n", mdsc);
> 

Thanks,
-- 
Jeff Layton <jlayton@kernel.org>