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

[Ming Lei <ming.lei@redhat.com>]

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().

-- 
Ming