linux-kernel - Re: [PATCH BUGFIX] block, bfq: update wr_busy

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Date:   Mon, 19 Jun 2017 15:38:19 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Paolo Valente <paolo.valente@...aro.org>
Cc:     kbuild-all@...org, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, broonie@...nel.org,
        Paolo Valente <paolo.valente@...aro.org>
Subject: Re: [PATCH BUGFIX] block, bfq: update wr_busy_queues if needed on a
 queue split

Hi Paolo,

[auto build test WARNING on v4.12-rc5]
[also build test WARNING on next-20170616]
[cannot apply to block/for-next]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Paolo-Valente/block-bfq-update-wr_busy_queues-if-needed-on-a-queue-split/20170619-145003
config: i386-randconfig-x000-201725 (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   block/bfq-iosched.c: In function 'bfq_get_rq_private':
>> block/bfq-iosched.c:770:10: warning: 'old_wr_coeff' may be used uninitialized in this function [-Wmaybe-uninitialized]
     else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
             ^
   block/bfq-iosched.c:731:15: note: 'old_wr_coeff' was declared here
     unsigned int old_wr_coeff;
                  ^~~~~~~~~~~~

vim +/old_wr_coeff +770 block/bfq-iosched.c

   754		    time_is_before_jiffies(bfqq->last_wr_start_finish +
   755					   bfqq->wr_cur_max_time))) {
   756			bfq_log_bfqq(bfqq->bfqd, bfqq,
   757			    "resume state: switching off wr");
   758	
   759			bfqq->wr_coeff = 1;
   760		}
   761	
   762		/* make sure weight will be updated, however we got here */
   763		bfqq->entity.prio_changed = 1;
   764	
   765		if (likely(!busy))
   766			return;
   767	
   768		if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
   769			bfqd->wr_busy_queues++;
 > 770		else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
   771			bfqd->wr_busy_queues--;
   772	}
   773	
   774	static int bfqq_process_refs(struct bfq_queue *bfqq)
   775	{
   776		return bfqq->ref - bfqq->allocated - bfqq->entity.on_st;
   777	}
   778	

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