Re: [PATCH] blk-iocost: fix lockdep warning on blkcg->lock

[Jens Axboe <axboe@kernel.dk>]

On 8/3/21 7:02 AM, Jens Axboe wrote:
> On 8/3/21 1:06 AM, Ming Lei wrote:
>> blkcg->lock depends on q->queue_lock which may depend on another driver
>> lock required in irq context, one example is dm-thin:
>>
>> 	Chain exists of:
>> 	  &pool->lock#3 --> &q->queue_lock --> &blkcg->lock
>>
>> 	 Possible interrupt unsafe locking scenario:
>>
>> 	       CPU0                    CPU1
>> 	       ----                    ----
>> 	  lock(&blkcg->lock);
>> 	                               local_irq_disable();
>> 	                               lock(&pool->lock#3);
>> 	                               lock(&q->queue_lock);
>> 	  <Interrupt>
>> 	    lock(&pool->lock#3);
>>
>> Fix the issue by using spin_lock_irq(&blkcg->lock) in ioc_weight_write().
> 
> This looks fine to me for blk-iocost, but block/blk-cgroup.c:blkg_create()
> also looks like it gets the IRQ state of the same lock wrong?

Ah, that one is under the queue lock, so irqs are already disabled.

-- 
Jens Axboe