Re: [PATCH v3] scsi/sd: release scan_mutex during sync_cache and start_stop

[Song Liu <songliubraving@fb.com>]

> On Feb 8, 2017, at 2:53 PM, Song Liu <songliubraving@fb.com> wrote:
> 
> When a device is deleted through sysfs handle "delete", the code
> locks shost->scan_mutex. If multiple devices are deleted at the
> same time, these deletes will be handled in series.
> 
> On the other hand, sd_shutdown() sometimes issues long latency
> commands: sync cache and start_stop. It is not necessary for these
> commands to run in series.
> 
> To reduce latency of parallel "delete" requests, this patch unlock
> shost->scan_mutex before long latency commands and relock the mutex
> after the command.
> 
> Fixed bug from previous version.
> 
> Reported-by: kernel test robot <fengguang.wu@intel.com>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
> drivers/scsi/sd.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> index 9e0783b..14c5815 100644
> --- a/drivers/scsi/sd.c
> +++ b/drivers/scsi/sd.c
> @@ -3304,6 +3304,9 @@ static int sd_start_stop_device(struct scsi_disk *sdkp, int start)
> static void sd_shutdown(struct device *dev)
> {
> 	struct scsi_disk *sdkp = dev_get_drvdata(dev);
> +	struct scsi_device *sdev;
> +	struct Scsi_Host *shost;
> +	int try_lock_scan_mutex;
> 
> 	if (!sdkp)
> 		return;         /* this can happen */
> @@ -3311,15 +3314,26 @@ static void sd_shutdown(struct device *dev)
> 	if (pm_runtime_suspended(dev))
> 		return;
> 
> +	sdev = sdkp->device;
> +	shost = sdev->host;
> +	try_lock_scan_mutex = mutex_trylock(&shost->scan_mutex);
> +
> 	if (sdkp->WCE && sdkp->media_present) {
> +		mutex_unlock(&shost->scan_mutex);
> 		sd_printk(KERN_NOTICE, sdkp, "Synchronizing SCSI cache\n");
> 		sd_sync_cache(sdkp);
> +		mutex_lock(&shost->scan_mutex);
> 	}
> 
> 	if (system_state != SYSTEM_RESTART && sdkp->device->manage_start_stop) {
> +		mutex_unlock(&shost->scan_mutex);
> 		sd_printk(KERN_NOTICE, sdkp, "Stopping disk\n");
> 		sd_start_stop_device(sdkp, 0);
> +		mutex_lock(&shost->scan_mutex);
> 	}
> +
> +	if (try_lock_scan_mutex)
> +		mutex_unlock(&shost->scan_mutex);
> }
> 
> static int sd_suspend_common(struct device *dev, bool ignore_stop_errors)
> -- 
> 2.9.3
> 

Forgot to CC Christoph