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

[Alan Stern <stern@rowland.harvard.edu>]

On Tue, Jun 30, 2020 at 11:17:34AM -0400, 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.
> 
> This patch simplifies the situation considerably by adding the missing
> function call directly into blk_set_runtime_active().  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>

Please disregard this patch.  When I wrote it, I didn't realize that 
blk_clear_pm_only() is meant to be used like a reference counter (it's a 
bad choice of name, since the routine does a decrement rather than a 
clear -- and likewise for blk_set_pm_only()).

I'll submit a revised patch later.

Alan Stern


>  block/blk-pm.c         |   25 ++++++++++---------------
>  drivers/scsi/scsi_pm.c |   10 ++--------
>  2 files changed, 12 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);
>  
> @@ -204,6 +195,9 @@ 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)
>  {
> @@ -213,6 +207,7 @@ void blk_set_runtime_active(struct reque
>  		pm_runtime_mark_last_busy(q->dev);
>  		pm_request_autosuspend(q->dev);
>  		spin_unlock_irq(&q->queue_lock);
> +		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);
>  		}
>  	}
>  
>