On 16.11.18 г. 10:22 ч., Qu Wenruo wrote:
> 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;
>
> Again, it's the stupid compiler needs some hint for the fact that
> we will always enter the while loop for at least once, thus @slot should
> always be initialized.
>
> Fix it by assign level after the BUG_ON(), so the stupid compiler knows
> we will always go into the while loop.
>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
Much better, thank you:
Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
> ---
> changelog:
> v1.1:
> Better commit message, with the original warning report and
> how compiler thinks this could be a problem.
> ---
> ctree.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/ctree.c b/ctree.c
> index 46e2ccedc0bf..9c9cb0dfdbf2 100644
> --- a/ctree.c
> +++ b/ctree.c
> @@ -2961,11 +2961,12 @@ int btrfs_next_sibling_tree_block(struct btrfs_fs_info *fs_info,
> struct btrfs_path *path)
> {
> int slot;
> - int level = path->lowest_level + 1;
> + int level;
> struct extent_buffer *c;
> struct extent_buffer *next = NULL;
>
> BUG_ON(path->lowest_level + 1 >= BTRFS_MAX_LEVEL);
> + level = path->lowest_level + 1;
> while(level < BTRFS_MAX_LEVEL) {
> if (!path->nodes[level])
> return 1;
>
