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SubjectRe: [PATCH] bcache: avoid clang -Wunintialized warning
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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@arndb.de>
>> ---
>> 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

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