> Il giorno 09 feb 2018, alle ore 20:18, Jens Axboe <axboe@xxxxxxxxx> ha scritto:
>
> On 2/9/18 12:14 PM, Bart Van Assche wrote:
>> On 02/09/18 10:58, Jens Axboe wrote:
>>> On 2/9/18 11:54 AM, Bart Van Assche wrote:
>>>> Hello Paolo,
>>>>
>>>> If I enable the BFQ scheduler for a dm-mpath device then a kernel oops
>>>> appears (see also below). This happens systematically with Linus' tree from
>>>> this morning (commit 54ce685cae30) merged with Jens' for-linus branch (commit
>>>> a78773906147 ("block, bfq: add requeue-request hook")) and for-next branch
>>>> (commit 88455ad7f928). Is this a known issue?
>>>
>>> Does it happen on Linus -git as well, or just with my for-linus merged in?
>>> What I'm getting at is if a78773906147 caused this or not.
>>
>> Hello Jens,
>>
>> Thanks for chiming in. After having reverted commit a78773906147, after
>> having rebuilt the BFQ scheduler, after having rebooted and after having
>> repeated the test I see the same kernel oops being reported. I think
>> that means that this regression is not caused by commit a78773906147. In
>> case it would be useful, here is how gdb translates the crash address:
>>
>> $ gdb block/bfq*ko
>> (gdb) list *(bfq_remove_request+0x8d)
>> 0x280d is in bfq_remove_request (block/bfq-iosched.c:1760).
>> 1755 list_del_init(&rq->queuelist);
>> 1756 bfqq->queued[sync]--;
>> 1757 bfqd->queued--;
>> 1758 elv_rb_del(&bfqq->sort_list, rq);
>> 1759
>> 1760 elv_rqhash_del(q, rq);
>> 1761 if (q->last_merge == rq)
>> 1762 q->last_merge = NULL;
>> 1763
>> 1764 if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
>
> Looks very odd. So clearly RQF_HASHED is set, but we're blowing up on
> the hash list pointers. I'll let Paolo take a look at this one. Thanks
> for testing without that commit, I want to push out my pending fixes
> today and this would have thrown a wrench in the works.
>
Also this smells a little bit like some spurious elevator call.
Unfortunately I have no clue on the cause. To go on, I need at least
to reproduce it. In this respect: Bart, could you please tell me how
to setup the offending configuration, and to cause the failure?
Possibly with just one, or at most two PCs. I don't have fancier hw
at the moment.
Thanks,
Paolo
> --
> Jens Axboe
