md/bitmap: It is OK to clear bits during recovery.

commit d0a4bb492772ce5c4bdfba3744a99ed6f6fb238f introduced a
regression which is annoying but fairly harmless.

When writing to an array that is undergoing recovery (a spare
in being integrated into the array), writing to the array will
set bits in the bitmap, but they will not be cleared when the
write completes.

For bits covering areas that have not been recovered yet this is not a
problem as the recovery will clear the bits.  However bits set in
already-recovered region will stay set and never be cleared.
This doesn't risk data integrity.  The only negatives are:
 - next time there is a crash, more resyncing than necessary will
   be done.
 - the bitmap doesn't look clean, which is confusing.

While an array is recovering we don't want to update the
'events_cleared' setting in the bitmap but we do still want to clear
bits that have very recently been set - providing they were written to
the recovering device.

So split those two needs - which previously both depended on 'success'
and always clear the bit of the write went to all devices.

Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/bitmap.c

@@ -1393,9 +1393,6 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto
 			 atomic_read(&bitmap->behind_writes),
 			 bitmap->mddev->bitmap_info.max_write_behind);
 	}
-	if (bitmap->mddev->degraded)
-		/* Never clear bits or update events_cleared when degraded */
-		success = 0;
 
 	while (sectors) {
 		sector_t blocks;
@@ -1409,7 +1406,7 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto
 			return;
 		}
 
-		if (success &&
+		if (success && !bitmap->mddev->degraded &&
 		    bitmap->events_cleared < bitmap->mddev->events) {
 			bitmap->events_cleared = bitmap->mddev->events;
 			bitmap->need_sync = 1;