Re: [PATCH] block: Fix potential deadlock warning in blk_mq_mark_tag_wait

[Bart Van Assche <bvanassche@acm.org>]

On 8/14/24 4:35 AM, Li Lingfeng wrote:
> When interrupt is turned on while a lock holding by spin_lock_irq it
> throws a warning because of potential deadlock.

Which tool reported the warning? Please mention this in the patch
description.
> 
> blk_mq_mark_tag_wait
>   spin_lock_irq(&wq->lock)
>        --> turn off interrupt and get lockA
>   blk_mq_get_driver_tag
>    __blk_mq_tag_busy
>     spin_lock_irq(&tags->lock)
>     spin_unlock_irq(&tags->lock)
>        --> release lockB and turn on interrupt accidentally

The above call chain does not match the code in Linus' master tree.
Please fix this.

> Fix it by using spin_lock_irqsave to get lockB instead of spin_lock_irq.
> Fixes: 4f1731df60f9 ("blk-mq: fix potential io hang by wrong 'wake_batch'")
> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>

Please leave a blank line between the patch description and the section
with tags.

> -	spin_lock_irq(&tags->lock);
> +	spin_lock_irqsave(&tags->lock, flags);
>   	users = tags->active_queues + 1;
>   	WRITE_ONCE(tags->active_queues, users);
>   	blk_mq_update_wake_batch(tags, users);
> -	spin_unlock_irq(&tags->lock);
> +	spin_unlock_irqrestore(&tags->lock, flags);
>   }

The code changes however look good to me.

Thanks,

Bart.