Re: [PATCH v2] SCSI and block: Simplify resume handling

From: Can Guo <cang@codeaurora.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Bart Van Assche <bvanassche@acm.org>,
	martin.petersen@oracle.com, linux-scsi@vger.kernel.org,
	linux-block@vger.kernel.org
Subject: Re: [PATCH v2] SCSI and block: Simplify resume handling
Date: Wed, 22 Jul 2020 09:46:10 +0800	[thread overview]
Message-ID: <d2605929ee63b3a2386bc01965202950@codeaurora.org> (raw)
In-Reply-To: <20200701183718.GA507293@rowland.harvard.edu>

Hi Alan,

On 2020-07-02 02:37, Alan Stern wrote:
> Commit 05d18ae1cc8a ("scsi: pm: Balance pm_only counter of request
> queue during system resume") fixed a problem in the block layer's
> runtime-PM code: blk_set_runtime_active() failed to call
> blk_clear_pm_only().  However, the commit's implementation was
> awkward; it forced the SCSI system-resume handler to choose whether to
> call blk_post_runtime_resume() or blk_set_runtime_active(), depending
> on whether or not the SCSI device had previously been runtime
> suspended.
> 

Yeah, even I thoght it was awkward as I couldn't find a way or a 
existing
API to fix it subtly without changing block layer. I was trying not to
make noise to block layer as I am not an expert of it, so I chose the 
akward
way to keep the fix within driver layer. Anyways, thanks for the change 
and
I will come back after I test it.

Can Guo.

> This patch simplifies the situation considerably by adding the missing
> function call directly into blk_set_runtime_active() (under the
> condition that the queue is not already in the RPM_ACTIVE state).
> This allows the SCSI routine to revert back to its original form.
> Furthermore, making this change reveals that blk_post_runtime_resume()
> (in its success pathway) does exactly the same thing as
> blk_set_runtime_active().  The duplicate code is easily removed by
> making one routine call the other.
> 
> No functional changes are intended.
> 
> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
> CC: Can Guo <cang@codeaurora.org>
> CC: Bart Van Assche <bvanassche@acm.org>
> 
> ---
> 
> v2:	Don't call blk_clear_pm_only() if the queue's RPM status was
> 	already set to RPM_ACTIVE.  This happens during a system resume
> 	if the device was not in runtime suspend beforehand.
> 
> Martin:
> 
> Since you merged the oritinal 05d18ae1cc8a commit, I'm submitting this 
> to
> you as an update.  If you would prefer to have it go by way of the
> block-layer tree, let me know and I'll resend it.
> 
> 
> [as1939b]
> 
> 
>  block/blk-pm.c         |   30 +++++++++++++++---------------
>  drivers/scsi/scsi_pm.c |   10 ++--------
>  2 files changed, 17 insertions(+), 23 deletions(-)
> 
> Index: usb-devel/block/blk-pm.c
> ===================================================================
> --- usb-devel.orig/block/blk-pm.c
> +++ usb-devel/block/blk-pm.c
> @@ -164,30 +164,21 @@ EXPORT_SYMBOL(blk_pre_runtime_resume);
>   *
>   * Description:
>   *    Update the queue's runtime status according to the return value 
> of the
> - *    device's runtime_resume function. If it is successfully resumed, 
> process
> - *    the requests that are queued into the device's queue when it is 
> resuming
> - *    and then mark last busy and initiate autosuspend for it.
> + *    device's runtime_resume function. If the resume was successful, 
> call
> + *    blk_set_runtime_active() to do the real work of restarting the 
> queue.
>   *
>   *    This function should be called near the end of the device's
>   *    runtime_resume callback.
>   */
>  void blk_post_runtime_resume(struct request_queue *q, int err)
>  {
> -	if (!q->dev)
> -		return;
> -
> -	spin_lock_irq(&q->queue_lock);
>  	if (!err) {
> -		q->rpm_status = RPM_ACTIVE;
> -		pm_runtime_mark_last_busy(q->dev);
> -		pm_request_autosuspend(q->dev);
> -	} else {
> +		blk_set_runtime_active(q);
> +	} else if (q->dev) {
> +		spin_lock_irq(&q->queue_lock);
>  		q->rpm_status = RPM_SUSPENDED;
> +		spin_unlock_irq(&q->queue_lock);
>  	}
> -	spin_unlock_irq(&q->queue_lock);
> -
> -	if (!err)
> -		blk_clear_pm_only(q);
>  }
>  EXPORT_SYMBOL(blk_post_runtime_resume);
> 
> @@ -204,15 +195,24 @@ EXPORT_SYMBOL(blk_post_runtime_resume);
>   * This function can be used in driver's resume hook to correct queue
>   * runtime PM status and re-enable peeking requests from the queue. It
>   * should be called before first request is added to the queue.
> + *
> + * This function is also called by blk_post_runtime_resume() for 
> successful
> + * runtime resumes.  It does everything necessary to restart the 
> queue.
>   */
>  void blk_set_runtime_active(struct request_queue *q)
>  {
>  	if (q->dev) {
> +		int old_status;
> +
>  		spin_lock_irq(&q->queue_lock);
> +		old_status = q->rpm_status;
>  		q->rpm_status = RPM_ACTIVE;
>  		pm_runtime_mark_last_busy(q->dev);
>  		pm_request_autosuspend(q->dev);
>  		spin_unlock_irq(&q->queue_lock);
> +
> +		if (old_status != RPM_ACTIVE)
> +			blk_clear_pm_only(q);
>  	}
>  }
>  EXPORT_SYMBOL(blk_set_runtime_active);
> Index: usb-devel/drivers/scsi/scsi_pm.c
> ===================================================================
> --- usb-devel.orig/drivers/scsi/scsi_pm.c
> +++ usb-devel/drivers/scsi/scsi_pm.c
> @@ -80,10 +80,6 @@ static int scsi_dev_type_resume(struct d
>  	dev_dbg(dev, "scsi resume: %d\n", err);
> 
>  	if (err == 0) {
> -		bool was_runtime_suspended;
> -
> -		was_runtime_suspended = pm_runtime_suspended(dev);
> -
>  		pm_runtime_disable(dev);
>  		err = pm_runtime_set_active(dev);
>  		pm_runtime_enable(dev);
> @@ -97,10 +93,8 @@ static int scsi_dev_type_resume(struct d
>  		 */
>  		if (!err && scsi_is_sdev_device(dev)) {
>  			struct scsi_device *sdev = to_scsi_device(dev);
> -			if (was_runtime_suspended)
> -				blk_post_runtime_resume(sdev->request_queue, 0);
> -			else
> -				blk_set_runtime_active(sdev->request_queue);
> +
> +			blk_set_runtime_active(sdev->request_queue);
>  		}
>  	}