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
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