On Wed, Dec 05, 2018 at 02:40:12PM +0800, 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;
>
> 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.
I was hoping that we can actually add the hint to BUG_ON so the code
does not continue if the condition is true.
