Re: [PATCH 1/2] scsi: sas: flush destruct workqueue on device unregister

[John Garry]

On 29/03/2017 12:29, Johannes Thumshirn wrote:
> On Wed, Mar 29, 2017 at 12:15:44PM +0100, John Garry wrote:
> > On 29/03/2017 10:41, Johannes Thumshirn wrote:
> > > In the advent of an SAS device unregister we have to wait for all destruct
> > > works to be done to not accidently delay deletion of a SAS rphy or it's
> > > children to the point when we're removing the SCSI or SAS hosts.
> > >
> > > Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
> > > ---
> > > drivers/scsi/libsas/sas_discover.c | 4 ++++
> > > 1 file changed, 4 insertions(+)
> > >
> > > diff --git a/drivers/scsi/libsas/sas_discover.c b/drivers/scsi/libsas/sas_discover.c
> > > index 60de662..75b18f1 100644
> > > --- a/drivers/scsi/libsas/sas_discover.c
> > > +++ b/drivers/scsi/libsas/sas_discover.c
> > > @@ -382,9 +382,13 @@ void sas_unregister_dev(struct asd_sas_port *port, struct domain_device *dev)
> > > 	}
> > >
> > > 	if (!test_and_set_bit(SAS_DEV_DESTROY, &dev->state)) {
> > > +		struct sas_discovery *disc = &dev->port->disc;
> > > +		struct sas_work *sw = &disc->disc_work[DISCE_DESTRUCT].work;
> > > +
> > > 		sas_rphy_unlink(dev->rphy);
> > > 		list_move_tail(&dev->disco_list_node, &port->destroy_list);
> > > 		sas_discover_event(dev->port, DISCE_DESTRUCT);
> > > +		flush_work(&sw->work);
> >
> > I quickly tested plugging out the expander and we never get past this call
> > to flush - a hang results:
>
> Can you activat lockdep so we can see which lock it is that we're blocking on?

I have it on:
CONFIG_LOCKDEP_SUPPORT=y
CONFIG_LOCKD=y
CONFIG_LOCKD_V4=y

> It's most likely in sas_unregister_common_dev() but this function takes two spin
> locks, port->dev_list_lock and ha->lock.

We can see from the callstack I provided that we're working in workqueue 
scsi_wq_0 and trying to flush that same queue.

Much appreciated,
John

> Thanks a lot,
>        Johannes