linux-kernel - Re: [PATCH 1/2] PM: runtime: Fix I/O hang due to race between resume and runtime disable

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Message-ID: <dc4dba4f-8334-40ea-8c53-6e8d135f1d41@acm.org>
Date: Wed, 26 Nov 2025 13:10:46 -0800
From: Bart Van Assche <bvanassche@....org>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Yang Yang <yang.yang@...o.com>, Jens Axboe <axboe@...nel.dk>,
 Pavel Machek <pavel@...nel.org>, Len Brown <lenb@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH 1/2] PM: runtime: Fix I/O hang due to race between resume
 and runtime disable

On 11/26/25 12:17 PM, Rafael J. Wysocki wrote:
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -309,6 +309,8 @@ int blk_queue_enter(struct request_queue
>   		if (flags & BLK_MQ_REQ_NOWAIT)
>   			return -EAGAIN;
>   
> +		/* if necessary, resume .dev (assume success). */
> +		blk_pm_resume_queue(pm, q);
>   		/*
>   		 * read pair of barrier in blk_freeze_queue_start(), we need to
>   		 * order reading __PERCPU_REF_DEAD flag of .q_usage_counter and

blk_queue_enter() may be called from the suspend path so I don't think
that the above change will work. As an example, the UFS driver submits a
SCSI START STOP UNIT command from its runtime suspend callback. The call
chain is as follows:

   ufshcd_wl_runtime_suspend()
     __ufshcd_wl_suspend()
       ufshcd_set_dev_pwr_mode()
         ufshcd_execute_start_stop()
           scsi_execute_cmd()
             scsi_alloc_request()
               blk_queue_enter()
             blk_execute_rq()
             blk_mq_free_request()
               blk_queue_exit()

Thanks,

Bart.