md/md-llbitmap: raise barrier before state machine transition

Move the barrier raise operation before calling llbitmap_state_machine()
in both llbitmap_start_write() and llbitmap_start_discard(). This
ensures the barrier is in place before any state transitions occur,
preventing potential race conditions where the state machine could
complete before the barrier is properly raised.

Cc: stable@vger.kernel.org
Fixes: 5ab829f ("md/md-llbitmap: introduce new lockless bitmap")
Link: https://lore.kernel.org/linux-raid/20260223024038.3084853-3-yukuai@fnnas.com
Signed-off-by: Yu Kuai <yukuai@fnnas.com>

Author: hailan94

drivers/md/md-llbitmap.c

@@ -1070,12 +1070,12 @@ static void llbitmap_start_write(struct mddev *mddev, sector_t offset,
 	int page_start = (start + BITMAP_DATA_OFFSET) >> PAGE_SHIFT;
 	int page_end = (end + BITMAP_DATA_OFFSET) >> PAGE_SHIFT;
 
-	llbitmap_state_machine(llbitmap, start, end, BitmapActionStartwrite);
-
 	while (page_start <= page_end) {
 		llbitmap_raise_barrier(llbitmap, page_start);
 		page_start++;
 	}
+
+	llbitmap_state_machine(llbitmap, start, end, BitmapActionStartwrite);
 }
 
 static void llbitmap_end_write(struct mddev *mddev, sector_t offset,
@@ -1102,12 +1102,12 @@ static void llbitmap_start_discard(struct mddev *mddev, sector_t offset,
 	int page_start = (start + BITMAP_DATA_OFFSET) >> PAGE_SHIFT;
 	int page_end = (end + BITMAP_DATA_OFFSET) >> PAGE_SHIFT;
 
-	llbitmap_state_machine(llbitmap, start, end, BitmapActionDiscard);
-
 	while (page_start <= page_end) {
 		llbitmap_raise_barrier(llbitmap, page_start);
 		page_start++;
 	}
+
+	llbitmap_state_machine(llbitmap, start, end, BitmapActionDiscard);
 }
 
 static void llbitmap_end_discard(struct mddev *mddev, sector_t offset,