dm: fix queue start/stop imbalance under suspend/load/resume races

When suspend and load run concurrently, before q->mq_ops is set in
blk_mq_init_allocated_queue(), __dm_suspend() skip dm_stop_queue(). As a
result, the queue's quiesce depth is not incremented.

Later, once table load has finished and __dm_resume() runs, which triggers
q->quiesce_depth ==0 warning in blk_mq_unquiesce_queue():
Call Trace:
 <TASK>
 dm_start_queue+0x16/0x20 [dm_mod]
 __dm_resume+0xac/0xb0 [dm_mod]
 dm_resume+0x12d/0x150 [dm_mod]
 do_resume+0x2c2/0x420 [dm_mod]
 dev_suspend+0x30/0x130 [dm_mod]
 ctl_ioctl+0x402/0x570 [dm_mod]
 dm_ctl_ioctl+0x23/0x30 [dm_mod]

Fix this by explicitly tracking whether the request queue was
stopped in __dm_suspend() via a new DMF_QUEUE_STOPPED flag.
Only call dm_start_queue() in __dm_resume() if the queue was
actually stopped.

Fixes: e70feb8 ("blk-mq: support concurrent queue quiesce/unquiesce")
Cc: stable@vger.kernel.org
Signed-off-by: Zheng Qixing <zhengqixing@huawei.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: Zheng Qixing

drivers/md/dm-core.h

@@ -162,6 +162,7 @@ struct mapped_device {
 #define DMF_SUSPENDED_INTERNALLY 7
 #define DMF_POST_SUSPENDING 8
 #define DMF_EMULATE_ZONE_APPEND 9
+#define DMF_QUEUE_STOPPED 10
 
 static inline sector_t dm_get_size(struct mapped_device *md)
 {

drivers/md/dm.c

@@ -2960,8 +2960,10 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
 	 * Stop md->queue before flushing md->wq in case request-based
 	 * dm defers requests to md->wq from md->queue.
 	 */
-	if (dm_request_based(md))
+	if (dm_request_based(md)) {
 		dm_stop_queue(md->queue);
+		set_bit(DMF_QUEUE_STOPPED, &md->flags);
+	}
 
 	flush_workqueue(md->wq);
 
@@ -2983,7 +2985,7 @@ static int __dm_suspend(struct mapped_device *md, struct dm_table *map,
 	if (r < 0) {
 		dm_queue_flush(md);
 
-		if (dm_request_based(md))
+		if (test_and_clear_bit(DMF_QUEUE_STOPPED, &md->flags))
 			dm_start_queue(md->queue);
 
 		unlock_fs(md);
@@ -3067,7 +3069,7 @@ static int __dm_resume(struct mapped_device *md, struct dm_table *map)
 	 * so that mapping of targets can work correctly.
 	 * Request-based dm is queueing the deferred I/Os in its request_queue.
 	 */
-	if (dm_request_based(md))
+	if (test_and_clear_bit(DMF_QUEUE_STOPPED, &md->flags))
 		dm_start_queue(md->queue);
 
 	unlock_fs(md);