Re: [PATCH -next v2 8/9] block: fix null-pointer dereference in ioc_pd_init

Tejun Heo
2022-12-01T10:31:49Z

On Thu, Dec 01, 2022 at 06:23:16PM +0800, Yu Kuai wrote:
> Hi,
>
> 在 2022/12/01 18:11, Tejun Heo 写道:
> > On Thu, Dec 01, 2022 at 10:12:13AM +0800, Yu Kuai wrote:
> > > 1) By mentioning that "del_gendisk() is quiescing the queue", do you
> > > suggest to add rcu_read_lock()? This seems wrong because blk_iocost_init
> > > requires memory allocation.
> >
> > Quiescing uses SRCU so that should be fine but I'm not sure whether this is
> > the right one to piggyback on. Jens should have a better idea.
> >
> > Thanks.
> >
>
> Currently SRCU is used if BLK_MQ_F_BLOCKING set, otherwise RCU is used.
>
> dispatch:
> #define __blk_mq_run_dispatch_ops(q, check_sleep, dispatch_ops) \
> do { \
> if ((q)->tag_set->flags & BLK_MQ_F_BLOCKING) { \
> int srcu_idx; \
> \
> might_sleep_if(check_sleep); \
> srcu_idx = srcu_read_lock((q)->tag_set->srcu); \
> (dispatch_ops); \
> srcu_read_unlock((q)->tag_set->srcu, srcu_idx); \
> } else { \
> rcu_read_lock(); \
> (dispatch_ops); \
> rcu_read_unlock(); \
> } \
> } while (0)
>
> quiesce:
> void blk_mq_wait_quiesce_done(struct blk_mq_tag_set *set)
> {
> if (set->flags & BLK_MQ_F_BLOCKING)
> synchronize_srcu(set->srcu);
> else
> synchronize_rcu();
> }

Oh I see. Unfortunately, I don't know what to do off the top of my head.

Thanks.

--
tejun