On 8/18/23 9:12 PM, chengming.zhou@xxxxxxxxx wrote: > From: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> > > IO scheduler has requirement that one request which has been inserted > must call finish_request() only once. > > Now we have three special cases to consider: > 1. rq has not insert, has complete: e.g. empty preflush > 2. rq has insert, has not complete: e.g. merged requests will be freed > 3. rq has insert, has twice complete: e.g. postflushes > > Note case 1 which existed before, has been no problem since all the > schedulers will check in their finish_request() if the rq has been > inserted or not, like checking "rq->elv.priv[0]". > > Then case 2 and case 3 are the introduced regression, we moved the > scheduler finish_request() from free phase to complete phase to solve > a deadlock problem. But it caused no finish_request() for request in > case 2, and double finish_request() for request in case 3. > > So we still need finish_request() in blk_mq_free_request() to cover > case 2. And clear RQF_USE_SCHED flag to avoid double finish_request(). > It should be fine since we're freeing the request now anyway. > > Of course, we can also make all schedulers' finish_request() to clear > "rq->elv.priv[0]" to avoid double finish. Or clear it in blk-mq, make > the rq like not inserted as case 1. > > FYI it's easy to reproduce warning in mq-deadline using this: > ``` > DEV=sdb > echo mq-deadline > /sys/block/$DEV/queue/scheduler > mkfs.ext4 /dev/$DEV > mount /dev/$DEV /mnt > cd /mnt > stress-ng --symlink 4 --timeout 60 > echo none > /sys/block/$DEV/queue/scheduler > ``` > > Reported-by: kernel test robot <oliver.sang@xxxxxxxxx> > Closes: https://lore.kernel.org/oe-lkp/202308172100.8ce4b853-oliver.sang@xxxxxxxxx > Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx> I folded in this one and added a link to it as well, final result is here: https://git.kernel.dk/cgit/linux/commit/?h=block-6.5&id=e5c0ca13659e9d18f53368d651ed7e6e433ec1cf I'll get this sent off today. -- Jens Axboe
