md: raid5: fix clearing of biofill operations

ops_complete_biofill() runs outside of spin_lock(&sh->lock) and clears the
'pending' and 'ack' bits.  Since the test_and_ack_op() macro only checks
against 'complete' it can get an inconsistent snapshot of pending work.

Move the clearing of these bits to handle_stripe5(), under the lock.
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Tested-by: Joel Bertrand <joel.bertrand@systella.fr>
Signed-off-by: Neil Brown <neilb@suse.de>
Cc: Stable <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/md/raid5.c

@@ -376,7 +376,12 @@ static unsigned long get_stripe_work(struct stripe_head *sh)
 		ack++;
 
 	sh->ops.count -= ack;
-	BUG_ON(sh->ops.count < 0);
+	if (unlikely(sh->ops.count < 0)) {
+		printk(KERN_ERR "pending: %#lx ops.pending: %#lx ops.ack: %#lx "
+			"ops.complete: %#lx\n", pending, sh->ops.pending,
+			sh->ops.ack, sh->ops.complete);
+		BUG();
+	}
 
 	return pending;
 }
@@ -550,8 +555,7 @@ static void ops_complete_biofill(void *stripe_head_ref)
 			}
 		}
 	}
-	clear_bit(STRIPE_OP_BIOFILL, &sh->ops.ack);
-	clear_bit(STRIPE_OP_BIOFILL, &sh->ops.pending);
+	set_bit(STRIPE_OP_BIOFILL, &sh->ops.complete);
 
 	return_io(return_bi);
 
@@ -2893,6 +2897,13 @@ static void handle_stripe6(struct stripe_head *sh, struct page *tmp_page)
 	s.expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
 	/* Now to look around and see what can be done */
 
+	/* clean-up completed biofill operations */
+	if (test_bit(STRIPE_OP_BIOFILL, &sh->ops.complete)) {
+		clear_bit(STRIPE_OP_BIOFILL, &sh->ops.pending);
+		clear_bit(STRIPE_OP_BIOFILL, &sh->ops.ack);
+		clear_bit(STRIPE_OP_BIOFILL, &sh->ops.complete);
+	}
+
 	rcu_read_lock();
 	for (i=disks; i--; ) {
 		mdk_rdev_t *rdev;