md/raid10: unify handling of write completion.

A write can complete at two different places:
1/ when the last member-device write completes, through
   raid10_end_write_request
2/ in make_request() when we remove the initial bias from ->remaining.

These two should do exactly the same thing and the comment says they
do, but they don't.

So factor the correct code out into a function and call it in both
places.  This makes the code much more similar to RAID1.

The difference is only significant if there is an error, and they
usually take a while, so it is unlikely that there will be an error
already when make_request is completing, so this is unlikely to cause
real problems.
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid10.c

@@ -337,6 +337,21 @@ static void close_write(r10bio_t *r10_bio)
 	md_write_end(r10_bio->mddev);
 }
 
+static void one_write_done(r10bio_t *r10_bio)
+{
+	if (atomic_dec_and_test(&r10_bio->remaining)) {
+		if (test_bit(R10BIO_WriteError, &r10_bio->state))
+			reschedule_retry(r10_bio);
+		else {
+			close_write(r10_bio);
+			if (test_bit(R10BIO_MadeGood, &r10_bio->state))
+				reschedule_retry(r10_bio);
+			else
+				raid_end_bio_io(r10_bio);
+		}
+	}
+}
+
 static void raid10_end_write_request(struct bio *bio, int error)
 {
 	int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
@@ -387,17 +402,7 @@ static void raid10_end_write_request(struct bio *bio, int error)
 	 * Let's see if all mirrored write operations have finished
 	 * already.
 	 */
-	if (atomic_dec_and_test(&r10_bio->remaining)) {
-		if (test_bit(R10BIO_WriteError, &r10_bio->state))
-			reschedule_retry(r10_bio);
-		else {
-			close_write(r10_bio);
-			if (test_bit(R10BIO_MadeGood, &r10_bio->state))
-				reschedule_retry(r10_bio);
-			else
-				raid_end_bio_io(r10_bio);
-		}
-	}
+	one_write_done(r10_bio);
 	if (dec_rdev)
 		rdev_dec_pending(conf->mirrors[dev].rdev, conf->mddev);
 }
@@ -1127,15 +1132,8 @@ static int make_request(mddev_t *mddev, struct bio * bio)
 		spin_unlock_irqrestore(&conf->device_lock, flags);
 	}
 
-	if (atomic_dec_and_test(&r10_bio->remaining)) {
-		/* This matches the end of raid10_end_write_request() */
-		bitmap_endwrite(r10_bio->mddev->bitmap, r10_bio->sector,
-				r10_bio->sectors,
-				!test_bit(R10BIO_Degraded, &r10_bio->state),
-				0);
-		md_write_end(mddev);
-		raid_end_bio_io(r10_bio);
-	}
+	/* Remove the bias on 'remaining' */
+	one_write_done(r10_bio);
 
 	/* In case raid10d snuck in to freeze_array */
 	wake_up(&conf->wait_barrier);