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 ef0ff68351be ("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: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 49821f138ae02a248bea5b45e602561ffb3a2497..8128165a46fab658532e0b100e852939dad20555 100644 (file)
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -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);

diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index 3a5dfbb81622f7360ffe8dc243a584045ecc78c7..cbdf61c1d667fe41972248d12448487c887c5bad 100644 (file)
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -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();
        }

diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index 5f21547b2ad26bce1e5385e5720279ae8ff8a563..cc2859d76d811dae9817930a046ad31c5e2e66d2 100644 (file)
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -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

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index f3564e406160a17f703713c2d11ac9832cfd3453..2ba7eef4105a7d4da3dea2ec9ce6d8d129559c3a 100644 (file)
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -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);