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

From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@redhat.com>
Cc: linux-block@vger.kernel.org, Tejun Heo <tj@kernel.org>,
	Bruno Goncalves <bgoncalv@redhat.com>
Subject: Re: [PATCH] blk-iocost: fix lockdep warning on blkcg->lock
Date: Tue, 3 Aug 2021 19:34:03 -0600	[thread overview]
Message-ID: <fefbae5d-18ed-2150-8dc6-a3e271a49c5f@kernel.dk> (raw)
In-Reply-To: <YQnskyUwX+3icYyU@T590>

On 8/3/21 7:25 PM, Ming Lei wrote:
> On Tue, Aug 03, 2021 at 07:02:28AM -0600, 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?
> 
> blkg_create() is called with irq disabled in all three callers: 
> blkg_lookup_create(), blkg_conf_prep() and blkcg_init_queue().

Yes I know, see email sent 1 min after the one you're replying to.

-- 
Jens Axboe