Block: use a freezable workqueue for disk-event polling

This patch (as1519) fixes a bug in the block layer's disk-events
polling.  The polling is done by a work routine queued on the
system_nrt_wq workqueue.  Since that workqueue isn't freezable, the
polling continues even in the middle of a system sleep transition.

Obviously, polling a suspended drive for media changes and such isn't
a good thing to do; in the case of USB mass-storage devices it can
lead to real problems requiring device resets and even re-enumeration.

The patch fixes things by creating a new system-wide, non-reentrant,
freezable workqueue and using it for disk-events polling.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -1478,9 +1478,9 @@ static void __disk_unblock_events(struct gendisk *disk, bool check_now)
 	intv = disk_events_poll_jiffies(disk);
 	set_timer_slack(&ev->dwork.timer, intv / 4);
 	if (check_now)
-		queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
+		queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, 0);
 	else if (intv)
-		queue_delayed_work(system_nrt_wq, &ev->dwork, intv);
+		queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, intv);
 out_unlock:
 	spin_unlock_irqrestore(&ev->lock, flags);
 }
@@ -1524,7 +1524,7 @@ void disk_flush_events(struct gendisk *disk, unsigned int mask)
 	ev->clearing |= mask;
 	if (!ev->block) {
 		cancel_delayed_work(&ev->dwork);
-		queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
+		queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, 0);
 	}
 	spin_unlock_irq(&ev->lock);
 }
@@ -1561,7 +1561,7 @@ unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask)
 
 	/* uncondtionally schedule event check and wait for it to finish */
 	disk_block_events(disk);
-	queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
+	queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, 0);
 	flush_delayed_work(&ev->dwork);
 	__disk_unblock_events(disk, false);
 
@@ -1598,7 +1598,7 @@ static void disk_events_workfn(struct work_struct *work)
 
 	intv = disk_events_poll_jiffies(disk);
 	if (!ev->block && intv)
-		queue_delayed_work(system_nrt_wq, &ev->dwork, intv);
+		queue_delayed_work(system_nrt_freezable_wq, &ev->dwork, intv);
 
 	spin_unlock_irq(&ev->lock);
 

include/linux/workqueue.h

@@ -289,12 +289,16 @@ enum {
  *
  * system_freezable_wq is equivalent to system_wq except that it's
  * freezable.
+ *
+ * system_nrt_freezable_wq is equivalent to system_nrt_wq except that
+ * it's freezable.
  */
 extern struct workqueue_struct *system_wq;
 extern struct workqueue_struct *system_long_wq;
 extern struct workqueue_struct *system_nrt_wq;
 extern struct workqueue_struct *system_unbound_wq;
 extern struct workqueue_struct *system_freezable_wq;
+extern struct workqueue_struct *system_nrt_freezable_wq;
 
 extern struct workqueue_struct *
 __alloc_workqueue_key(const char *fmt, unsigned int flags, int max_active,

kernel/workqueue.c

@@ -253,11 +253,13 @@ struct workqueue_struct *system_long_wq __read_mostly;
 struct workqueue_struct *system_nrt_wq __read_mostly;
 struct workqueue_struct *system_unbound_wq __read_mostly;
 struct workqueue_struct *system_freezable_wq __read_mostly;
+struct workqueue_struct *system_nrt_freezable_wq __read_mostly;
 EXPORT_SYMBOL_GPL(system_wq);
 EXPORT_SYMBOL_GPL(system_long_wq);
 EXPORT_SYMBOL_GPL(system_nrt_wq);
 EXPORT_SYMBOL_GPL(system_unbound_wq);
 EXPORT_SYMBOL_GPL(system_freezable_wq);
+EXPORT_SYMBOL_GPL(system_nrt_freezable_wq);
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/workqueue.h>
@@ -3833,8 +3835,11 @@ static int __init init_workqueues(void)
 					    WQ_UNBOUND_MAX_ACTIVE);
 	system_freezable_wq = alloc_workqueue("events_freezable",
 					      WQ_FREEZABLE, 0);
+	system_nrt_freezable_wq = alloc_workqueue("events_nrt_freezable",
+			WQ_NON_REENTRANT | WQ_FREEZABLE, 0);
 	BUG_ON(!system_wq || !system_long_wq || !system_nrt_wq ||
-	       !system_unbound_wq || !system_freezable_wq);
+	       !system_unbound_wq || !system_freezable_wq ||
+		!system_nrt_freezable_wq);
 	return 0;
 }
 early_initcall(init_workqueues);