btrfs: initialize start_slot in btrfs_log_prealloc_extents

[ Upstream commit b4c639f699349880b7918b861e1bd360442ec450 ]

Jens reported a compiler warning when using
CONFIG_CC_OPTIMIZE_FOR_SIZE=y that looks like this

  fs/btrfs/tree-log.c: In function ‘btrfs_log_prealloc_extents’:
  fs/btrfs/tree-log.c:4828:23: warning: ‘start_slot’ may be used
  uninitialized [-Wmaybe-uninitialized]
   4828 |                 ret = copy_items(trans, inode, dst_path, path,
	|                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   4829 |                                  start_slot, ins_nr, 1, 0);
	|                                  ~~~~~~~~~~~~~~~~~~~~~~~~~
  fs/btrfs/tree-log.c:4725:13: note: ‘start_slot’ was declared here
   4725 |         int start_slot;
	|             ^~~~~~~~~~

The compiler is incorrect, as we only use this code when ins_len > 0,
and when ins_len > 0 we have start_slot properly initialized.  However
we generally find the -Wmaybe-uninitialized warnings valuable, so
initialize start_slot to get rid of the warning.

Reported-by: Jens Axboe <axboe@kernel.dk>
Tested-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 2407a231d9ad40913c9ccefe26a26666a13c2038..f73a1438a6ac1953cad8e086017e407549cf0b8d 100644 (file)
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4191,7 +4191,7 @@ static int btrfs_log_prealloc_extents(struct btrfs_trans_handle *trans,
        struct extent_buffer *leaf;
        int slot;
        int ins_nr = 0;
-       int start_slot;
+       int start_slot = 0;
        int ret;
 
        if (!(inode->flags & BTRFS_INODE_PREALLOC))