Messages in this thread | | | Subject | Re: [PATCH] sbitmap: avoid maybe-uninitialized warning | From | Jens Axboe <> | Date | Mon, 19 Sep 2016 09:22:34 -0600 |
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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
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