On 2019/4/26 9:01 下午, Nathan Chancellor wrote:
> On Fri, Apr 26, 2019 at 10:43:01AM +0800, Coly Li wrote:
>> On 2019/4/26 2:08 上午, Nathan Chancellor wrote:
>>> On Fri, Mar 22, 2019 at 03:35:00PM +0100, Arnd Bergmann wrote:
>>>> clang has identified a code path in which it thinks a
>>>> variable may be unused:
>>>>
>>>> drivers/md/bcache/alloc.c:333:4: error: variable 'bucket' is used uninitialized whenever 'if' condition is false
>>>> [-Werror,-Wsometimes-uninitialized]
>>>> fifo_pop(&ca->free_inc, bucket);
>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>> drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop'
>>>> #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i))
>>>> ^~~~~~~~~~~~~~~~~~~~~~~~~
>>>> drivers/md/bcache/util.h:189:6: note: expanded from macro 'fifo_pop_front'
>>>> if (_r) { \
>>>> ^~
>>>> drivers/md/bcache/alloc.c:343:46: note: uninitialized use occurs here
>>>> allocator_wait(ca, bch_allocator_push(ca, bucket));
>>>> ^~~~~~
>>>> drivers/md/bcache/alloc.c:287:7: note: expanded from macro 'allocator_wait'
>>>> if (cond) \
>>>> ^~~~
>>>> drivers/md/bcache/alloc.c:333:4: note: remove the 'if' if its condition is always true
>>>> fifo_pop(&ca->free_inc, bucket);
>>>> ^
>>>> drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop'
>>>> #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i))
>>>> ^
>>>> drivers/md/bcache/util.h:189:2: note: expanded from macro 'fifo_pop_front'
>>>> if (_r) { \
>>>> ^
>>>> drivers/md/bcache/alloc.c:331:15: note: initialize the variable 'bucket' to silence this warning
>>>> long bucket;
>>>> ^
>>>>
>>>> This cannot happen in practice because we only enter the loop
>>>> if there is at least one element in the list.
>>>>
>>>> Slightly rearranging the code makes this clearer to both the
>>>> reader and the compiler, which avoids the warning.
>>>>
>>>> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
>>>> ---
>>>> drivers/md/bcache/alloc.c | 5 +++--
>>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c
>>>> index 5002838ea476..f8986effcb50 100644
>>>> --- a/drivers/md/bcache/alloc.c
>>>> +++ b/drivers/md/bcache/alloc.c
>>>> @@ -327,10 +327,11 @@ static int bch_allocator_thread(void *arg)
>>>> * possibly issue discards to them, then we add the bucket to
>>>> * the free list:
>>>> */
>>>> - while (!fifo_empty(&ca->free_inc)) {
>>>> + while (1) {
>>>> long bucket;
>>>>
>>>> - fifo_pop(&ca->free_inc, bucket);
>>>> + if (!fifo_pop(&ca->free_inc, bucket))
>>>> + break;
>>>>
>>>> if (ca->discard) {
>>>> mutex_unlock(&ca->set->bucket_lock);
>>>> --
>>>> 2.20.0
>>>>
>>>
>>> Hi all,
>>>
>>> Could someone please review/pick this up? This is one of two remaining
>>> -Wsometimes-uninitialized warnings among arm, arm64, and x86_64
>>> all{yes,mod}config and I'd like to get it turned on as soon as possible
>>> to catch more bugs.
>>
>> Hi Nathan,
>>
>> It is in Jens' block tree for-next branch already, for Linux v5.2 merge
>> window.
>>
>> Thanks.
>>
>> --
>>
>> Coly Li
>
> Hi Coly,
>
> Thank you for the reply and heads up, it hadn't hit -next when I sent
> that message and I didn't check Jens' tree.
>
> I appreciate you picking it up!
Hi Nathan,
You are welcome, and thanks for the contribution to make bcache better :-)
--
Coly Li
