md/bitmap: rename and tidy up BITMAP_PAGE_CLEAN

The flag 'BITMAP_PAGE_CLEAN' has a confusing name as it doesn't mean
that the page is clean, but rather that there are counters in the page
which allow bits in the bitmap to be cleared - i.e. maybe cleaning can
happen.

So change it to BITMAP_PAGE_PENDING and fix some irregularities:
 - Don't set it in bitmap_init_from_disk as bitmap_set_memory_bits
   sets it when needed
 - in bitmap_daemon_work, if we find a counter that is '1', but
   need_sync is set, then set BITMAP_PAGE_PENDING again (it was
   recently cleared) to ensure we don't forget about this bit.

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

drivers/md/bitmap.c

@@ -868,7 +868,8 @@ static void bitmap_file_kick(struct bitmap *bitmap)
 
 enum bitmap_page_attr {
 	BITMAP_PAGE_DIRTY = 0,     /* there are set bits that need to be synced */
-	BITMAP_PAGE_CLEAN = 1,     /* there are bits that might need to be cleared */
+	BITMAP_PAGE_PENDING = 1,   /* there are bits that are being cleaned.
+				    * i.e. counter is 1 or 2. */
 	BITMAP_PAGE_NEEDWRITE = 2, /* there are cleared bits that need to be synced */
 };
 
@@ -1111,7 +1112,6 @@ static int bitmap_init_from_disk(struct bitmap *bitmap, sector_t start)
 					       (sector_t)i << CHUNK_BLOCK_SHIFT(bitmap),
 					       needed);
 			bit_cnt++;
-			set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
 		}
 	}
 
@@ -1204,7 +1204,7 @@ void bitmap_daemon_work(mddev_t *mddev)
 
 		if (page != lastpage) {
 			/* skip this page unless it's marked as needing cleaning */
-			if (!test_page_attr(bitmap, page, BITMAP_PAGE_CLEAN)) {
+			if (!test_page_attr(bitmap, page, BITMAP_PAGE_PENDING)) {
 				int need_write = test_page_attr(bitmap, page,
 								BITMAP_PAGE_NEEDWRITE);
 				if (need_write)
@@ -1249,19 +1249,17 @@ void bitmap_daemon_work(mddev_t *mddev)
 			}
 			spin_lock_irqsave(&bitmap->lock, flags);
 			if (!bitmap->need_sync)
-				clear_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
+				clear_page_attr(bitmap, page, BITMAP_PAGE_PENDING);
 		}
 		bmc = bitmap_get_counter(bitmap,
 					 (sector_t)j << CHUNK_BLOCK_SHIFT(bitmap),
 					 &blocks, 0);
-		if (bmc) {
-			if (*bmc)
+		if (!bmc)
+			j |= PAGE_COUNTER_MASK;
+		else if (*bmc) {
 			bitmap->allclean = 0;
 
-			if (*bmc == 2) {
-				*bmc = 1; /* maybe clear the bit next time */
-				set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
-			} else if (*bmc == 1 && !bitmap->need_sync) {
+			if (*bmc == 1 && !bitmap->need_sync) {
 				/* we can clear the bit */
 				*bmc = 0;
 				bitmap_count_page(bitmap,
@@ -1279,9 +1277,11 @@ void bitmap_daemon_work(mddev_t *mddev)
 								 j),
 						paddr);
 				kunmap_atomic(paddr, KM_USER0);
+			} else if (*bmc <= 2) {
+				*bmc = 1; /* maybe clear the bit next time */
+				set_page_attr(bitmap, page, BITMAP_PAGE_PENDING);
+			}
 		}
-		} else
-			j |= PAGE_COUNTER_MASK;
 	}
 	spin_unlock_irqrestore(&bitmap->lock, flags);
 
@@ -1458,7 +1458,7 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto
 				      filemap_get_page(
 					      bitmap,
 					      offset >> CHUNK_BLOCK_SHIFT(bitmap)),
-				      BITMAP_PAGE_CLEAN);
+				      BITMAP_PAGE_PENDING);
 
 		spin_unlock_irqrestore(&bitmap->lock, flags);
 		offset += blocks;
@@ -1546,7 +1546,7 @@ void bitmap_end_sync(struct bitmap *bitmap, sector_t offset, sector_t *blocks, i
 			if (*bmc <= 2)
 				set_page_attr(bitmap,
 					      filemap_get_page(bitmap, offset >> CHUNK_BLOCK_SHIFT(bitmap)),
-					      BITMAP_PAGE_CLEAN);
+					      BITMAP_PAGE_PENDING);
 		}
 	}
  unlock:
@@ -1622,7 +1622,7 @@ static void bitmap_set_memory_bits(struct bitmap *bitmap, sector_t offset, int n
 		*bmc = 1 | (needed ? NEEDED_MASK : 0);
 		bitmap_count_page(bitmap, offset, 1);
 		page = filemap_get_page(bitmap, offset >> CHUNK_BLOCK_SHIFT(bitmap));
-		set_page_attr(bitmap, page, BITMAP_PAGE_CLEAN);
+		set_page_attr(bitmap, page, BITMAP_PAGE_PENDING);
 	}
 	spin_unlock_irq(&bitmap->lock);
 	bitmap->allclean = 0;