Commit f049cf1a authored by Bart Van Assche's avatar Bart Van Assche Committed by Martin K. Petersen
Browse files

scsi: sd: Rely on the driver core for asynchronous probing 



As explained during the 2018 LSF/MM session about increasing SCSI disk
probing concurrency, the problems with the current probing approach are as
follows:

 - The driver core is unaware of asynchronous SCSI LUN probing.
   wait_for_device_probe() waits for all asynchronous probes except
   asynchronous SCSI disk probes.

 - There is unnecessary serialization between sd_probe() and sd_remove().
   This can lead to a deadlock.

Hence this patch that modifies the sd driver such that it uses the driver
core framework for asynchronous probing. The async domain and
get_device()/put_device() pairs that became superfluous due to this change
are removed.

This patch does not affect the time needed for loading the scsi_debug
kernel module with parameters delay=0 and max_luns=256.

This patch depends on commit ef0ff683 ("driver core: Probe devices
asynchronously instead of the driver") that went upstream in kernel version
v5.1-rc1.

Cc: Lee Duncan <lduncan@suse.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarBart Van Assche <bvanassche@acm.org>
Reviewed-by: default avatarHannes Reinecke <hare@suse.com>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 50a1ea5b

drivers/scsi/scsi.c

+3 −9
Original line number Diff line number Diff line
@@ -86,15 +86,10 @@ unsigned int scsi_logging_level; 
EXPORT_SYMBOL(scsi_logging_level);

#endif



/* sd, scsi core and power management need to coordinate flushing async actions */

ASYNC_DOMAIN(scsi_sd_probe_domain);

EXPORT_SYMBOL(scsi_sd_probe_domain);



/*

 * Separate domain (from scsi_sd_probe_domain) to maximize the benefit of

 * asynchronous system resume operations.  It is marked 'exclusive' to avoid

 * being included in the async_synchronize_full() that is invoked by

 * dpm_resume()

 * Domain for asynchronous system resume operations.  It is marked 'exclusive'

 * to avoid being included in the async_synchronize_full() that is invoked by

 * dpm_resume().

 */

ASYNC_DOMAIN_EXCLUSIVE(scsi_sd_pm_domain);

EXPORT_SYMBOL(scsi_sd_pm_domain);
@@ -821,7 +816,6 @@ static void __exit exit_scsi(void) 
	scsi_exit_devinfo();

	scsi_exit_procfs();

	scsi_exit_queue();

	async_unregister_domain(&scsi_sd_probe_domain);

}



subsys_initcall(init_scsi);

drivers/scsi/scsi_pm.c

+1 −5
Original line number Diff line number Diff line
@@ -176,11 +176,7 @@ static int scsi_bus_resume_common(struct device *dev, 


static int scsi_bus_prepare(struct device *dev)

{

	if (scsi_is_sdev_device(dev)) {

		/* sd probing uses async_schedule.  Wait until it finishes. */

		async_synchronize_full_domain(&scsi_sd_probe_domain);



	} else if (scsi_is_host_device(dev)) {

	if (scsi_is_host_device(dev)) {

		/* Wait until async scanning is finished */

		scsi_complete_async_scans();

	}

drivers/scsi/scsi_priv.h

+0 −1
Original line number Diff line number Diff line
@@ -175,7 +175,6 @@ static inline void scsi_autopm_put_host(struct Scsi_Host *h) {} 
#endif /* CONFIG_PM */



extern struct async_domain scsi_sd_pm_domain;

extern struct async_domain scsi_sd_probe_domain;



/* scsi_dh.c */

#ifdef CONFIG_SCSI_DH

drivers/scsi/sd.c

+3 −9
Original line number Diff line number Diff line
@@ -568,6 +568,7 @@ static struct scsi_driver sd_template = { 
		.name		= "sd",

		.owner		= THIS_MODULE,

		.probe		= sd_probe,

		.probe_type	= PROBE_PREFER_ASYNCHRONOUS,

		.remove		= sd_remove,

		.shutdown	= sd_shutdown,

		.pm		= &sd_pm_ops,
@@ -3253,12 +3254,8 @@ static int sd_format_disk_name(char *prefix, int index, char *buf, int buflen) 
	return 0;

}



/*

 * The asynchronous part of sd_probe

 */

static void sd_probe_async(void *data, async_cookie_t cookie)

static void sd_probe_part2(struct scsi_disk *sdkp)

{

	struct scsi_disk *sdkp = data;

	struct scsi_device *sdp;

	struct gendisk *gd;

	u32 index;
@@ -3313,7 +3310,6 @@ static void sd_probe_async(void *data, async_cookie_t cookie) 
	sd_printk(KERN_NOTICE, sdkp, "Attached SCSI %sdisk\n",

		  sdp->removable ? "removable " : "");

	scsi_autopm_put_device(sdp);

	put_device(&sdkp->dev);

}



/**
@@ -3405,8 +3401,7 @@ static int sd_probe(struct device *dev) 
	get_device(dev);

	dev_set_drvdata(dev, sdkp);



	get_device(&sdkp->dev);	/* prevent release before async_schedule */

	async_schedule_domain(sd_probe_async, sdkp, &scsi_sd_probe_domain);

	sd_probe_part2(sdkp);



	return 0;
@@ -3442,7 +3437,6 @@ static int sd_remove(struct device *dev) 
	scsi_autopm_get_device(sdkp->device);



	async_synchronize_full_domain(&scsi_sd_pm_domain);

	async_synchronize_full_domain(&scsi_sd_probe_domain);

	device_del(&sdkp->dev);

	del_gendisk(sdkp->disk);

	sd_shutdown(dev);

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