linux-kernel - [PATCH AUTOSEL 6.5 08/18] btrfs: initialize start_slot in btrfs_log_prealloc

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Date:   Sat,  7 Oct 2023 20:48:42 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Josef Bacik <josef@...icpanda.com>, Jens Axboe <axboe@...nel.dk>,
        David Sterba <dsterba@...e.com>,
        Sasha Levin <sashal@...nel.org>, clm@...com,
        linux-btrfs@...r.kernel.org
Subject: [PATCH AUTOSEL 6.5 08/18] btrfs: initialize start_slot in btrfs_log_prealloc_extents

From: Josef Bacik <josef@...icpanda.com>

[ 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@...nel.dk>
Tested-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Josef Bacik <josef@...icpanda.com>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/btrfs/tree-log.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 365a1cc0a3c35..a00e7a0bc713d 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4722,7 +4722,7 @@ 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))
-- 
2.40.1