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

On 8/3/21 7:25 PM, Ming Lei wrote:

On Tue, Aug 03, 2021 at 07:02:28AM -0600, Jens Axboe wrote:

quoted

On 8/3/21 1:06 AM, Ming Lei wrote:

quoted

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