GCC 8.2.1 will report the following warning with "make W=1": ctree.c: In function 'btrfs_next_sibling_tree_block': ctree.c:2990:21: warning: 'slot' may be used uninitialized in this function [-Wmaybe-uninitialized] path->slots[level] = slot; ~~~~~~~~~~~~~~~~~~~^~~~~~
The culprit is the following code: int slot; << Not initialized int level = path->lowest_level + 1; BUG_ON(path->lowest_level + 1 >= BTRFS_MAX_LEVEL); while(level < BTRFS_MAX_LEVEL) { slot = path->slots[level] + 1; ^^^^^^ but we initialize @slot here. ... } path->slots[level] = slot; It's possible that compiler doesn't get enough hint for BUG_ON() on lowest_level + 1 >= BTRFS_MAX_LEVEL case. Fix it by using a do {} while() loop other than while() {} loop, to ensure we will run the loop for at least once. Signed-off-by: Qu Wenruo <w...@suse.com> --- ctree.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/ctree.c b/ctree.c index 46e2ccedc0bf..867e8b60b199 100644 --- a/ctree.c +++ b/ctree.c @@ -2966,7 +2966,7 @@ int btrfs_next_sibling_tree_block(struct btrfs_fs_info *fs_info, struct extent_buffer *next = NULL; BUG_ON(path->lowest_level + 1 >= BTRFS_MAX_LEVEL); - while(level < BTRFS_MAX_LEVEL) { + do { if (!path->nodes[level]) return 1; @@ -2986,7 +2986,7 @@ int btrfs_next_sibling_tree_block(struct btrfs_fs_info *fs_info, if (!extent_buffer_uptodate(next)) return -EIO; break; - } + } while (level < BTRFS_MAX_LEVEL); path->slots[level] = slot; while(1) { level--; -- 2.19.2