linux-kernel - Re: [REGRESSION] bfq probe failed on 4.19-rc3

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Date:   Wed, 12 Sep 2018 10:58:45 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Jeff Moyer <jmoyer@...hat.com>,
        Paolo Valente <paolo.valente@...aro.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [REGRESSION] bfq probe failed on 4.19-rc3

On Tue, 11 Sep 2018 18:54:19 +0200,
Jens Axboe wrote:
> 
> On 9/11/18 10:51 AM, Jeff Moyer wrote:
> > Jens Axboe <axboe@...nel.dk> writes:
> > 
> >> On 9/11/18 10:48 AM, Jeff Moyer wrote:
> >>> Jens Axboe <axboe@...nel.dk> writes:
> >>>
> >>>> On 9/11/18 10:03 AM, Takashi Iwai wrote:
> >>>>> Hi,
> >>>>>
> >>>>> I noticed that bfq doesn't appear in the I/O scheduler list on
> >>>>> 4.19-rc3.  It seems that blkcg_policy_register() at the beginning of
> >>>>> bfq_init() returns -ENOSPC, hence the probe aborts silently.
> >>>>>
> >>>>> Is this already addressed?
> >>>>
> >>>> Haven't heard about this one before. What kernel did you last use that
> >>>> worked?
> >>>
> >>> I'm guessing you just need to update the maximum number of policies:
> >>>
> >>> /*
> >>>  * Maximum number of blkcg policies allowed to be registered concurrently.
> >>>  * Defined here to simplify include dependency.
> >>>  */
> >>> #define BLKCG_MAX_POLS          3
> >>
> >> That is my guess too, hence the suggestion to try and disable the
> >> iolatency policy. Just tried here without, and it works, rebooting
> >> with to verify that we're running out of policy slots.
> > 
> > Functions calling this function: blkcg_policy_register
> > 
> >   File                      Function       Line
> > 0 block/bfq-iosched.c       bfq_init       5675 ret =
> >                                                 blkcg_policy_register(&blkcg_pol
> >                                                 icy_bfq);
> > 1 block/blk-iolatency.c     iolatency_init  946 return
> >                                                 blkcg_policy_register(&blkcg_pol
> >                                                 icy_iolatency);
> > 2 block/blk-throttle.c      throtl_init    2511 return
> >                                                 blkcg_policy_register(&blkcg_pol
> >                                                 icy_throtl);
> > 3 block/cfq-iosched.c       cfq_init       4869 ret =
> >                                                 blkcg_policy_register(&blkcg_pol
> >                                                 icy_cfq);
> > 
> > And then there were 4...
> 
> Exactly. I'd bump it to 5 to leave room for one more, if we have to grow it
> again, probably worth it to make it dynamic. So for, not really needed. Takashi,
> can verify that the below fixes it up for you?

Yes, it works.

Tested-by: Takashi Iwai <tiwai@...e.de>


Thanks!

Takashi