raid5: remove unnecessary bitmap write optimization

Neil pointed out the bitmap write optimization in handle_stripe_clean_event()
is unnecessary, because the chance one stripe gets written twice in the mean
time is rare. We can always do a bitmap_startwrite when a write request is
added to a stripe and bitmap_endwrite after write request is done.  Delete the
optimization. With it, we can delete some cases of device_lock.
Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid5.c

@@ -2357,7 +2357,7 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, in
 	spin_lock_irq(&conf->device_lock);
 	if (forwrite) {
 		bip = &sh->dev[dd_idx].towrite;
-		if (*bip == NULL && sh->dev[dd_idx].written == NULL)
+		if (*bip == NULL)
 			firstwrite = 1;
 	} else
 		bip = &sh->dev[dd_idx].toread;
@@ -2458,6 +2458,7 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 		/* fail all writes first */
 		bi = sh->dev[i].towrite;
 		sh->dev[i].towrite = NULL;
+		spin_unlock_irq(&conf->device_lock);
 		if (bi) {
 			s->to_write--;
 			bitmap_end = 1;
@@ -2477,6 +2478,10 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 			}
 			bi = nextbi;
 		}
+		if (bitmap_end)
+			bitmap_endwrite(conf->mddev->bitmap, sh->sector,
+				STRIPE_SECTORS, 0, 0);
+		bitmap_end = 0;
 		/* and fail all 'written' */
 		bi = sh->dev[i].written;
 		sh->dev[i].written = NULL;
@@ -2516,7 +2521,6 @@ handle_failed_stripe(struct r5conf *conf, struct stripe_head *sh,
 				bi = nextbi;
 			}
 		}
-		spin_unlock_irq(&conf->device_lock);
 		if (bitmap_end)
 			bitmap_endwrite(conf->mddev->bitmap, sh->sector,
 					STRIPE_SECTORS, 0, 0);
@@ -2720,9 +2724,7 @@ static void handle_stripe_clean_event(struct r5conf *conf,
 				test_bit(R5_UPTODATE, &dev->flags)) {
 				/* We can return any write requests */
 				struct bio *wbi, *wbi2;
-				int bitmap_end = 0;
 				pr_debug("Return write for disc %d\n", i);
-				spin_lock_irq(&conf->device_lock);
 				wbi = dev->written;
 				dev->written = NULL;
 				while (wbi && wbi->bi_sector <
@@ -2735,12 +2737,7 @@ static void handle_stripe_clean_event(struct r5conf *conf,
 					}
 					wbi = wbi2;
 				}
-				if (dev->towrite == NULL)
-					bitmap_end = 1;
-				spin_unlock_irq(&conf->device_lock);
-				if (bitmap_end)
-					bitmap_endwrite(conf->mddev->bitmap,
-							sh->sector,
+				bitmap_endwrite(conf->mddev->bitmap, sh->sector,
 						STRIPE_SECTORS,
 					 !test_bit(STRIPE_DEGRADED, &sh->state),
 						0);