Re: [PATCH -next 2/3] md/raid10: convert resync_lock to use seqlock

[Logan Gunthorpe <logang@deltatee.com>]

On 2022-09-02 02:14, Yu Kuai wrote:
> Can you try the following patch? I'm running mdadm tests myself and I
> didn't see any problems yet.

Yes, that patch seems to fix the issue.

However, may I suggest we do this without trying to introduce new
helpers into wait.h? I suspect that could result in a fair amount of
bike shedding and delay. wait_event_cmd() is often used in situations 
where a specific lock type doesn't have a helper.

My stab at it is in a diff below which also fixes the bug. 

I'd also recommend somebody clean up that nasty condition in 
wait_barrier(). Put it into an appropriately named function
with some comments. As is, it is pretty much unreadable.

Logan

--


diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 0e3229ee1ebc..ae297bc870bd 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -934,22 +934,26 @@ static void flush_pending_writes(struct r10conf *conf)
  *    lower_barrier when the particular background IO completes.
  */
 
+#define wait_event_barrier_cmd(conf, cond, cmd) \
+	wait_event_cmd((conf)->wait_barrier, cond, \
+		       write_sequnlock_irq(&(conf)->resync_lock); cmd, \
+		       write_seqlock_irq(&(conf)->resync_lock))
+#define wait_event_barrier(conf, cond) wait_event_barrier_cmd(conf, cond, )
+
 static void raise_barrier(struct r10conf *conf, int force)
 {
 	write_seqlock_irq(&conf->resync_lock);
 	BUG_ON(force && !conf->barrier);
 
 	/* Wait until no block IO is waiting (unless 'force') */
-	wait_event_lock_irq(conf->wait_barrier, force || !conf->nr_waiting,
-			    conf->resync_lock.lock);
+	wait_event_barrier(conf, force || !conf->nr_waiting);
 
 	/* block any new IO from starting */
 	WRITE_ONCE(conf->barrier, conf->barrier + 1);
 
 	/* Now wait for all pending IO to complete */
-	wait_event_lock_irq(conf->wait_barrier,
-			    !atomic_read(&conf->nr_pending) && conf->barrier < RESYNC_DEPTH,
-			    conf->resync_lock.lock);
+	wait_event_barrier(conf, !atomic_read(&conf->nr_pending) &&
+			   conf->barrier < RESYNC_DEPTH);
 
 	write_sequnlock_irq(&conf->resync_lock);
 }
@@ -1007,20 +1011,19 @@ static bool wait_barrier(struct r10conf *conf, bool nowait)
 			ret = false;
 		} else {
 			raid10_log(conf->mddev, "wait barrier");
-			wait_event_lock_irq(conf->wait_barrier,
-					    !conf->barrier ||
-					    (atomic_read(&conf->nr_pending) &&
-					     bio_list &&
-					     (!bio_list_empty(&bio_list[0]) ||
-					      !bio_list_empty(&bio_list[1]))) ||
+			wait_event_barrier(conf,
+					   !conf->barrier ||
+					   (atomic_read(&conf->nr_pending) &&
+					    bio_list &&
+					    (!bio_list_empty(&bio_list[0]) ||
+					     !bio_list_empty(&bio_list[1]))) ||
 					     /* move on if recovery thread is
 					      * blocked by us
 					      */
-					     (conf->mddev->thread->tsk == current &&
-					      test_bit(MD_RECOVERY_RUNNING,
-						       &conf->mddev->recovery) &&
-					      conf->nr_queued > 0),
-					    conf->resync_lock.lock);
+					    (conf->mddev->thread->tsk == current &&
+					     test_bit(MD_RECOVERY_RUNNING,
+					       &conf->mddev->recovery) &&
+					     conf->nr_queued > 0));
 		}
 		conf->nr_waiting--;
 		if (!conf->nr_waiting)
@@ -1058,10 +1061,9 @@ static void freeze_array(struct r10conf *conf, int extra)
 	conf->array_freeze_pending++;
 	WRITE_ONCE(conf->barrier, conf->barrier + 1);
 	conf->nr_waiting++;
-	wait_event_lock_irq_cmd(conf->wait_barrier,
-				atomic_read(&conf->nr_pending) == conf->nr_queued+extra,
-				conf->resync_lock.lock,
-				flush_pending_writes(conf));
+	wait_event_barrier_cmd(conf,
+		atomic_read(&conf->nr_pending) == conf->nr_queued+extra,
+		flush_pending_writes(conf));
 
 	conf->array_freeze_pending--;
 	write_sequnlock_irq(&conf->resync_lock);