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

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Message-ID: <20170329112922.GB9183@linux-x5ow.site>
Date:   Wed, 29 Mar 2017 13:29:22 +0200
From:   Johannes Thumshirn <jthumshirn@...e.de>
To:     John Garry <john.garry@...wei.com>
Cc:     "Martin K . Petersen" <martin.petersen@...cle.com>,
        Tejun Heo <tj@...nel.org>,
        James Bottomley <jejb@...ux.vnet.ibm.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Jack Wang <jinpu.wang@...fitbricks.com>,
        Hannes Reinecke <hare@...e.de>,
        Linux SCSI Mailinglist <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] scsi: sas: flush destruct workqueue on device
 unregister

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@...e.de>
> >---
> > 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?

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

Thanks a lot,
       Johannes

-- 
Johannes Thumshirn                                          Storage
jthumshirn@...e.de                                +49 911 74053 689
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