Btrfs: fix trim 0 bytes after a device delete

A user reported a bug of btrfs's trim, that is we will trim 0 bytes
after a device delete.

The reproducer:

$ mkfs.btrfs disk1
$ mkfs.btrfs disk2
$ mount disk1 /mnt
$ fstrim -v /mnt
$ btrfs device add disk2 /mnt
$ btrfs device del disk1 /mnt
$ fstrim -v /mnt

This is because after we delete the device, the block group may start from
a non-zero place, which will confuse trim to discard nothing.

Reported-by: Lutz Euler <lutz.euler@freenet.de>
Signed-off-by: Liu Bo <liubo2009@cn.fujitsu.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 283af7a676a3..60bfe2d68547 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7886,9 +7886,16 @@ int btrfs_trim_fs(struct btrfs_root *root, struct fstrim_range *range)
         u64 start;
         u64 end;
         u64 trimmed = 0;
+        u64 total_bytes = btrfs_super_total_bytes(fs_info->super_copy);
         int ret = 0;
 
-        cache = btrfs_lookup_block_group(fs_info, range->start);
+        /*
+         * try to trim all FS space, our block group may start from non-zero.
+         */
+        if (range->len == total_bytes)
+                cache = btrfs_lookup_first_block_group(fs_info, range->start);
+        else
+                cache = btrfs_lookup_block_group(fs_info, range->start);
 
         while (cache) {
                 if (cache->key.objectid >= (range->start + range->len)) {