[PATCH 2/2] scsi: alua: Call scsi_device_put() from non-atomic context

[Bart Van Assche <bvanassche@acm.org>]

Since commit f93ed747e2c7 ("scsi: core: Release SCSI devices
synchronously"), scsi_device_put() might sleep. Avoid calling it from
alua_rtpg_queue() with the pg_lock held. The lock only pretects h->pg,
anyway. To avoid the pg being freed under us, because of a race with
another thread, take a temporary reference. In alua_rtpg_queue(), verify
that the pg still belongs to the sdev being passed before actually
queueing the RTPG.

This patch fixes the following smatch warning:

drivers/scsi/device_handler/scsi_dh_alua.c:1013 alua_rtpg_queue() warn: sleeping in atomic context

alua_check_vpd() <- disables preempt
-> alua_rtpg_queue()
   -> scsi_device_put()

Cc: Martin Wilck <mwilck@suse.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Sachin Sant <sachinp@linux.ibm.com>
Cc: Benjamin Block <bblock@linux.ibm.com>
Suggested-by: Martin Wilck <mwilck@suse.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 drivers/scsi/device_handler/scsi_dh_alua.c | 27 +++++++++++++++-------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c b/drivers/scsi/device_handler/scsi_dh_alua.c
index bd4ee294f5c7..49cc18a87473 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -354,6 +354,8 @@ static int alua_check_vpd(struct scsi_device *sdev, struct alua_dh_data *h,
 			    "%s: port group %x rel port %x\n",
 			    ALUA_DH_NAME, group_id, rel_port);
 
+	kref_get(&pg->kref);
+
 	/* Check for existing port group references */
 	spin_lock(&h->pg_lock);
 	old_pg = rcu_dereference_protected(h->pg, lockdep_is_held(&h->pg_lock));
@@ -373,11 +375,11 @@ static int alua_check_vpd(struct scsi_device *sdev, struct alua_dh_data *h,
 		list_add_rcu(&h->node, &pg->dh_list);
 	spin_unlock_irqrestore(&pg->lock, flags);
 
-	alua_rtpg_queue(rcu_dereference_protected(h->pg,
-						  lockdep_is_held(&h->pg_lock)),
-			sdev, NULL, true);
 	spin_unlock(&h->pg_lock);
 
+	alua_rtpg_queue(pg, sdev, NULL, true);
+	kref_put(&pg->kref, release_port_group);
+
 	if (old_pg)
 		kref_put(&old_pg->kref, release_port_group);
 
@@ -986,6 +988,9 @@ static bool alua_rtpg_queue(struct alua_port_group *pg,
 {
 	int start_queue = 0;
 	unsigned long flags;
+
+	might_sleep();
+
 	if (WARN_ON_ONCE(!pg) || scsi_device_get(sdev))
 		return false;
 
@@ -996,11 +1001,17 @@ static bool alua_rtpg_queue(struct alua_port_group *pg,
 		force = true;
 	}
 	if (pg->rtpg_sdev == NULL) {
-		pg->interval = 0;
-		pg->flags |= ALUA_PG_RUN_RTPG;
-		kref_get(&pg->kref);
-		pg->rtpg_sdev = sdev;
-		start_queue = 1;
+		struct alua_dh_data *h = sdev->handler_data;
+
+		rcu_read_lock();
+		if (h && rcu_dereference(h->pg) == pg) {
+			pg->interval = 0;
+			pg->flags |= ALUA_PG_RUN_RTPG;
+			kref_get(&pg->kref);
+			pg->rtpg_sdev = sdev;
+			start_queue = 1;
+		}
+		rcu_read_unlock();
 	} else if (!(pg->flags & ALUA_PG_RUN_RTPG) && force) {
 		pg->flags |= ALUA_PG_RUN_RTPG;
 		/* Do not queue if the worker is already running */