On 06/03/2021 04:32, Bart Van Assche wrote:
On 3/5/21 7:14 AM, John Garry wrote:diff --git a/block/blk.h b/block/blk.h index 3b53e44b967e..1a948bfd91e4 100644 --- a/block/blk.h +++ b/block/blk.h @@ -201,10 +201,29 @@ void elv_unregister_queue(struct request_queue *q); static inline void elevator_exit(struct request_queue *q, struct elevator_queue *e) { + struct blk_mq_tag_set *set = q->tag_set; + struct request_queue *tmp; + lockdep_assert_held(&q->sysfs_lock);+ mutex_lock(&set->tag_list_lock);+ list_for_each_entry(tmp, &set->tag_list, tag_set_list) { + if (tmp == q) + continue; + blk_mq_freeze_queue(tmp); + blk_mq_quiesce_queue(tmp); + } + blk_mq_sched_free_requests(q); __elevator_exit(q, e); + + list_for_each_entry(tmp, &set->tag_list, tag_set_list) { + if (tmp == q) + continue; + blk_mq_unquiesce_queue(tmp); + blk_mq_unfreeze_queue(tmp); + } + mutex_unlock(&set->tag_list_lock); }
Hi Bart,
This patch introduces nesting of tag_list_lock inside sysfs_lock. The latter is per request queue while the former can be shared across multiple request queues. Has it been analyzed whether this is safe?
Firstly - ignoring implementation details for a moment - this patch is to ensure that the concept is consistent with your suggestion and whether it is sound.
As for nested locking, I can analyze more, but I did assume that we don't care about locking-out sysfs intervention during this time. And it seems pretty difficult to avoid nesting the locks.
And further to this, I see that https://lore.kernel.org/linux-block/3aa5407c-0800-2482-597b-4264781a7eac@xxxxxxxxxxx/T/#mc3e3175642660578c0ae2a6c32185b1e34ec4b8a has a new interface for tagset quiesce, which could make this process more efficient.
Please let me know further thoughts. Thanks, John
