Btrfs: avoid unnecessarily locking inode when clearing a range

If the range being cleared was not marked for defrag and we are not
about to clear the range from the defrag status, we don't need to
lock and unlock the inode.
Signed-off-by: NFilipe Manana <fdmanana@suse.com>
Reviewed-by: NChris Mason <clm@fb.com>
Reviewed-by: NWang Shilong <wangshilong1991@gmail.com>
Signed-off-by: NChris Mason <clm@fb.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -1801,10 +1801,11 @@ static void btrfs_clear_bit_hook(void *private_data,
 	u64 len = state->end + 1 - state->start;
 	u32 num_extents = count_max_extents(len);
 
-	spin_lock(&inode->lock);
-	if ((state->state & EXTENT_DEFRAG) && (*bits & EXTENT_DEFRAG))
+	if ((state->state & EXTENT_DEFRAG) && (*bits & EXTENT_DEFRAG)) {
+		spin_lock(&inode->lock);
 		inode->defrag_bytes -= len;
-	spin_unlock(&inode->lock);
+		spin_unlock(&inode->lock);
+	}
 
 	/*
 	 * set_bit and clear bit hooks normally require _irqsave/restore