linux-kernel - Re: [PATCH] block: Fix potential deadlock warning in blk_mq_mark_tag

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Message-ID: <ad92f738-9ba5-4cfc-aef5-3918a35e77ec@acm.org>
Date: Wed, 14 Aug 2024 12:52:36 -0700
From: Bart Van Assche <bvanassche@....org>
To: Li Lingfeng <lilingfeng@...weicloud.com>, axboe@...nel.dk, hch@....de,
 jack@...e.cz, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: yukuai1@...weicloud.com, yukuai3@...wei.com, houtao1@...wei.com,
 yi.zhang@...wei.com, yangerkun@...wei.com, lilingfeng3@...wei.com
Subject: Re: [PATCH] block: Fix potential deadlock warning in
 blk_mq_mark_tag_wait

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@...wei.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.