Re: [PATCH 7/9] btrfs-progs: Fix Wmaybe-uninitialized warning

[Qu Wenruo <wqu@xxxxxxx>]

On 2018/11/16 下午4:13, Nikolay Borisov wrote:
> 
> 
> On 16.11.18 г. 9:54 ч., Qu Wenruo wrote:
>> The only location is the following code:
>>
>> 	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;
>> 		...
>> 	}
>> 	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>
> 
> I don't get this warning on gcc 7.3. Also from your changelog it's not
> really clear what the compiler is confused about.

My gcc 8.2.1 reports it with "make W=1"

I'll just update the commit message with the original report:

  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;
    ~~~~~~~~~~~~~~~~~~~^~~~~~

Thanks,
Qu

> 
> Codewise lgtm:
> 
> Reviewed-by: Nikolay Borisov <nborisov@xxxxxxxx>
> 
>> ---
>>  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;
>>