Re: [PATCH] block: put the reference of the io scheduler module after switching back

[Yu Kuai]

Hi!

在 2022/10/11 20:54, Yu Kuai 写道:
> Hi!
>
> 在 2022/10/11 18:21, Jinlong Chen 写道:
> > We got a reference of the io scheduler module in
> > blk_mq_elv_switch_none to prevent the module from
> > being removed. We need to put that reference back
> > once we are done.
>
> However, if blk_mq_elv_switch_none() failed due to OOM, and module
> reference is not acquired, blk_mq_elv_switch_back() will still be
> called. This seems not to be the right fix.

Please ignore this.

I got it now if switch none failed, old queue is not added to the list,
and later blk_lookup_qe_pair() will fail to lookup the queue.

Thanks,
Kuai
> Thanks,
> Kuai
> > Signed-off-by: Jinlong Chen <chenjinlong2016@xxxxxxxxxxx>
> > ---
> >   block/blk-mq.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 8070b6c10e8d..8dfe3bf3e599 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -4595,6 +4595,13 @@ static void blk_mq_elv_switch_back(struct 
> > list_head *head,
> >       mutex_lock(&q->sysfs_lock);
> >       elevator_switch(q, t);
> > +    /**
> > +     * We got a reference of the io scheduler module in
> > +     * blk_mq_elv_switch_none to prevent the module from
> > +     * being removed. We need to put that reference back
> > +     * once we are done.
> > +     */
> > +    module_put(t->elevator_owner);
> >       mutex_unlock(&q->sysfs_lock);
> >   }
>
> .