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btrfs-progs: Fix -Wmaybe-uninitialized warning 

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 <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo 2018-12-05 14:40:12 +08:00 committed by David Sterba
parent e27e36b989
commit bda00a4021
1 changed files with 2 additions and 2 deletions
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4
ctree.c
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@ -2967,7 +2967,7 @@ 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;
@ -2987,7 +2987,7 @@ 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--;