* [PATCH] sbitmap: avoid maybe-uninitialized warning
@ 2016-09-19 12:33 Arnd Bergmann
2016-09-19 14:43 ` Jens Axboe
0 siblings, 1 reply; 5+ messages in thread
From: Arnd Bergmann @ 2016-09-19 12:33 UTC (permalink / raw)
To: Jens Axboe; +Cc: Arnd Bergmann, Omar Sandoval, linux-block, linux-kernel
The sbitmap code that has just been turned into a library module
returns uninitialized data for sbitmap_weight(), as pointed out by
gcc when building with -Wmaybe-uninitialized:
lib/sbitmap.c: In function 'sbitmap_weight':
lib/sbitmap.c:179:9: error: 'weight' may be used uninitialized in this function [-Werror=maybe-uninitialized]
Note that the value is never initialized, we just add data on
top, so it is wrong regardless of sb->map_nr.
This adds the missing initialization.
Fixes: 88459642cba4 ("blk-mq: abstract tag allocation out into sbitmap library")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
lib/sbitmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index e40808921544..2cecf05c82fd 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -169,7 +169,7 @@ EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);
unsigned int sbitmap_weight(const struct sbitmap *sb)
{
- unsigned int i, weight;
+ unsigned int i, weight = 0;
for (i = 0; i < sb->map_nr; i++) {
const struct sbitmap_word *word = &sb->map[i];
--
2.9.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] sbitmap: avoid maybe-uninitialized warning
2016-09-19 12:33 [PATCH] sbitmap: avoid maybe-uninitialized warning Arnd Bergmann
@ 2016-09-19 14:43 ` Jens Axboe
2016-09-19 15:14 ` Arnd Bergmann
0 siblings, 1 reply; 5+ messages in thread
From: Jens Axboe @ 2016-09-19 14:43 UTC (permalink / raw)
To: Arnd Bergmann; +Cc: Omar Sandoval, linux-block, linux-kernel
On 09/19/2016 06:33 AM, Arnd Bergmann wrote:
> The sbitmap code that has just been turned into a library module
> returns uninitialized data for sbitmap_weight(), as pointed out by
> gcc when building with -Wmaybe-uninitialized:
>
> lib/sbitmap.c: In function 'sbitmap_weight':
> lib/sbitmap.c:179:9: error: 'weight' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>
> Note that the value is never initialized, we just add data on
> top, so it is wrong regardless of sb->map_nr.
>
> This adds the missing initialization.
Thanks Arnd, Colin sent the same patch and I applied it. Note that:
> Fixes: 88459642cba4 ("blk-mq: abstract tag allocation out into sbitmap library")
that isn't truly correct, that patch is just what moved the code. The
bug predates that commit.
--
Jens Axboe
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] sbitmap: avoid maybe-uninitialized warning
2016-09-19 14:43 ` Jens Axboe
@ 2016-09-19 15:14 ` Arnd Bergmann
2016-09-19 15:22 ` Jens Axboe
0 siblings, 1 reply; 5+ messages in thread
From: Arnd Bergmann @ 2016-09-19 15:14 UTC (permalink / raw)
To: Jens Axboe; +Cc: Omar Sandoval, linux-block, linux-kernel
On Monday, September 19, 2016 8:43:12 AM CEST Jens Axboe wrote:
> On 09/19/2016 06:33 AM, Arnd Bergmann wrote:
> > The sbitmap code that has just been turned into a library module
> > returns uninitialized data for sbitmap_weight(), as pointed out by
> > gcc when building with -Wmaybe-uninitialized:
> >
> > lib/sbitmap.c: In function 'sbitmap_weight':
> > lib/sbitmap.c:179:9: error: 'weight' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> >
> > Note that the value is never initialized, we just add data on
> > top, so it is wrong regardless of sb->map_nr.
> >
> > This adds the missing initialization.
>
> Thanks Arnd, Colin sent the same patch and I applied it. Note that:
Ok, thanks!
> > Fixes: 88459642cba4 ("blk-mq: abstract tag allocation out into sbitmap library")
>
> that isn't truly correct, that patch is just what moved the code. The
> bug predates that commit.
It's not important as long as the bug is fixed now, but I think it was
correct before that move, we just lost the 'used=0' initialization,
which also triggered the warning:
-static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
-{
- unsigned int i, used;
-
- for (i = 0, used = 0; i < bt->map_nr; i++) {
- struct blk_align_bitmap *bm = &bt->map[i];
-
- used += bitmap_weight(&bm->word, bm->depth);
}
- return bt->depth - used;
}
Arnd
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] sbitmap: avoid maybe-uninitialized warning
2016-09-19 15:14 ` Arnd Bergmann
@ 2016-09-19 15:22 ` Jens Axboe
2016-09-19 15:41 ` Omar Sandoval
0 siblings, 1 reply; 5+ messages in thread
From: Jens Axboe @ 2016-09-19 15:22 UTC (permalink / raw)
To: Arnd Bergmann; +Cc: Omar Sandoval, linux-block, linux-kernel
On 09/19/2016 09:14 AM, Arnd Bergmann wrote:
> On Monday, September 19, 2016 8:43:12 AM CEST Jens Axboe wrote:
>> On 09/19/2016 06:33 AM, Arnd Bergmann wrote:
>>> The sbitmap code that has just been turned into a library module
>>> returns uninitialized data for sbitmap_weight(), as pointed out by
>>> gcc when building with -Wmaybe-uninitialized:
>>>
>>> lib/sbitmap.c: In function 'sbitmap_weight':
>>> lib/sbitmap.c:179:9: error: 'weight' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>>
>>> Note that the value is never initialized, we just add data on
>>> top, so it is wrong regardless of sb->map_nr.
>>>
>>> This adds the missing initialization.
>>
>> Thanks Arnd, Colin sent the same patch and I applied it. Note that:
>
> Ok, thanks!
>
>>> Fixes: 88459642cba4 ("blk-mq: abstract tag allocation out into sbitmap library")
>>
>> that isn't truly correct, that patch is just what moved the code. The
>> bug predates that commit.
>
> It's not important as long as the bug is fixed now, but I think it was
> correct before that move, we just lost the 'used=0' initialization,
> which also triggered the warning:
>
> -static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
> -{
> - unsigned int i, used;
> -
> - for (i = 0, used = 0; i < bt->map_nr; i++) {
> - struct blk_align_bitmap *bm = &bt->map[i];
> -
> - used += bitmap_weight(&bm->word, bm->depth);
> }
>
> - return bt->depth - used;
> }
I missed that, as I generally never use double inits in for loops, but I
guess I did for this one. But you are right, the bug was introduced with
the recent move, so your Fixes was completely correct.
Omar loses a cookie.
--
Jens Axboe
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] sbitmap: avoid maybe-uninitialized warning
2016-09-19 15:22 ` Jens Axboe
@ 2016-09-19 15:41 ` Omar Sandoval
0 siblings, 0 replies; 5+ messages in thread
From: Omar Sandoval @ 2016-09-19 15:41 UTC (permalink / raw)
To: Jens Axboe; +Cc: Arnd Bergmann, Omar Sandoval, linux-block, linux-kernel
On Mon, Sep 19, 2016 at 09:22:34AM -0600, Jens Axboe wrote:
> On 09/19/2016 09:14 AM, Arnd Bergmann wrote:
> > On Monday, September 19, 2016 8:43:12 AM CEST Jens Axboe wrote:
> > > On 09/19/2016 06:33 AM, Arnd Bergmann wrote:
> > > > The sbitmap code that has just been turned into a library module
> > > > returns uninitialized data for sbitmap_weight(), as pointed out by
> > > > gcc when building with -Wmaybe-uninitialized:
> > > >
> > > > lib/sbitmap.c: In function 'sbitmap_weight':
> > > > lib/sbitmap.c:179:9: error: 'weight' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> > > >
> > > > Note that the value is never initialized, we just add data on
> > > > top, so it is wrong regardless of sb->map_nr.
> > > >
> > > > This adds the missing initialization.
> > >
> > > Thanks Arnd, Colin sent the same patch and I applied it. Note that:
> >
> > Ok, thanks!
> >
> > > > Fixes: 88459642cba4 ("blk-mq: abstract tag allocation out into sbitmap library")
> > >
> > > that isn't truly correct, that patch is just what moved the code. The
> > > bug predates that commit.
> >
> > It's not important as long as the bug is fixed now, but I think it was
> > correct before that move, we just lost the 'used=0' initialization,
> > which also triggered the warning:
> >
> > -static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
> > -{
> > - unsigned int i, used;
> > -
> > - for (i = 0, used = 0; i < bt->map_nr; i++) {
> > - struct blk_align_bitmap *bm = &bt->map[i];
> > -
> > - used += bitmap_weight(&bm->word, bm->depth);
> > }
> >
> > - return bt->depth - used;
> > }
>
> I missed that, as I generally never use double inits in for loops, but I
> guess I did for this one. But you are right, the bug was introduced with
> the recent move, so your Fixes was completely correct.
>
> Omar loses a cookie.
:(
Apparently we disable -Wmaybe-uninitialized by default since
6e8d666e9253 ("Disable "maybe-uninitialized" warning globally"), that's
probably why I didn't see this. My mistake, thanks Arnd and Colin.
--
Omar
^ permalink raw reply [flat|nested] 5+ messages in thread
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2016-09-19 12:33 [PATCH] sbitmap: avoid maybe-uninitialized warning Arnd Bergmann
2016-09-19 14:43 ` Jens Axboe
2016-09-19 15:14 ` Arnd Bergmann
2016-09-19 15:22 ` Jens Axboe
2016-09-19 15:41 ` Omar Sandoval
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