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

[Yu Kuai]

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();
}

Thanks,
Kuai