[PATCH] btrfs: Fix off-by-one error btrfs_trim_free_extents

[Nikolay Borisov <nborisov@suse.com>]

btrfs_trim_free_extents always caps the range it's going to trim based
on the size of the device. This happens if find_first_clear_extent_bit
detects that untrimmed range is past the last allocated range. Since it
doesn't have knowledge of the size of the device it just returns (u64)-1
for end. Then btrfs_trim_free_extents caps this to device->total_bytes.
However, btrfs_trim_free_extent calculates 'len' based off of the
actual usable end byte - in this case total_bytes - 1.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>

Fixes: 4d877687cbbc ("btrfs: Switch btrfs_trim_free_extents to find_first_clear_extent_bit")
---

David you might want to squash that in the 'Fixes' commit. With this I see 
generic/500 passing and also full xfstest didn't uncover any new regressions. 
 fs/btrfs/extent-tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d9e2e35700fd..5a4b81259413 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -11175,7 +11175,7 @@ static int btrfs_trim_free_extents(struct btrfs_device *device,
 		 * end of the device it will set end to -1, in this case it's up
 		 * to the caller to trim the value to the size of the device.
 		 */
-		end = min(end, device->total_bytes);
+		end = min(end, device->total_bytes - 1);
 		len = end - start + 1;
 
 		/* We didn't find any extents */
-- 
2.17.1