Re: [PATCH v5 3/3] scsi: async sd resume

[Dan Williams <dan.j.williams@intel.com>]

On Mon, 2014-03-17 at 11:20 -0700, Dan Williams wrote:
> On Sun, 2014-03-16 at 11:21 -0700, James Bottomley wrote:
> > On Sat, 2014-03-15 at 16:35 -0700, Dan Williams wrote:
> > > On Sat, Mar 15, 2014 at 2:47 PM, James Bottomley
> > > > Hm, OK, if this is tied at the hip to async scanning, why do you need
> > > > another async domain for it?  Why not just use the current async
> > > > scanning domain ... it will actually probably resolve a few nasty (but
> > > > wholly manufactured) races where scanning races with suspend.
> > > 
> > > I considered that initially, but it ends up destroying most/all of the
> > > benefit of doing it asynchronously.  This is due to the fact that
> > > scsi_sd_probe_domain is flushed by the async_synchronize_full()
> > > performed in dpm_resume().  We want userspace to resume while the disk
> > > may still be starting.
> > 
> > OK, finally got it, the new domain doesn't participate in
> > async_synchronize_full() but scsi_sd_probe_domain does (and has to
> > because of the device and module operations).  That might actually be
> > worth a comment somewhere.
> 
> Fair enough, see the comment added to the declaration of
> scsi_sd_pm_domain below.
> 
> BTW, these patches are independent.  Patch 1 and 2 can go through
> Tejun/libata and this one can go through you/scsi by itself.
> 

...and Tejun has now applied the ata bits for 3.15.

James, when you get a chance, please apply this latest version of patch
3 or otherwise let me know your disposition.

Regards,
Dan

(no changes since the version I sent on the 17th)

8<------
scsi: async sd resume

From: Dan Williams <dan.j.williams@intel.com>

async_schedule() sd resume work to allow disks and other devices to
resume in parallel.

This moves the entirety of scsi_device resume to an async context to
ensure that scsi_device_resume() remains ordered with respect to the
completion of the start/stop command.  For the duration of the resume,
new command submissions (that do not originate from the scsi-core) will
be deferred (BLKPREP_DEFER).

It adds a new ASYNC_DOMAIN_EXCLUSIVE(scsi_sd_pm_domain) as a container
of these operations.  Like scsi_sd_probe_domain it is flushed at
sd_remove() time to ensure async ops do not continue past the
end-of-life of the sdev.  The implementation explicitly refrains from
reusing scsi_sd_probe_domain directly for this purpose as it is flushed
at the end of dpm_resume(), potentially defeating some of the benefit.
Given sdevs are quiesced it is permissible for these resume operations
to bleed past the async_synchronize_full() calls made by the driver
core.

We defer the resolution of which pm callback to call until
scsi_dev_type_{suspend|resume} time and guarantee that the callback
parameter is never NULL.  With this in place the type of resume
operation is encoded in the async function identifier.

There is a concern that async resume could trigger PSU overload.  In the
enterprise, storage enclosures enforce staggered spin-up regardless of
what the kernel does making async scanning safe by default.  Outside of
that context a user can disable asynchronous scanning via a kernel
command line or CONFIG_SCSI_SCAN_ASYNC.  Honor that setting when
deciding whether to do resume asynchronously.

Inspired by Todd's analysis and initial proposal [2]:
https://01.org/suspendresume/blogs/tebrandt/2013/hard-disk-resume-optimization-simpler-approach

Cc: Len Brown <len.brown@intel.com>
Cc: Phillip Susi <psusi@ubuntu.com>
[alan: bug fix and clean up suggestion]
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Suggested-by: Todd Brandt <todd.e.brandt@linux.intel.com>
[djbw: kick all resume work to the async queue]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 drivers/scsi/Kconfig     |    3 +
 drivers/scsi/scsi.c      |    9 +++
 drivers/scsi/scsi_pm.c   |  128 ++++++++++++++++++++++++++++++++++++----------
 drivers/scsi/scsi_priv.h |    2 +
 drivers/scsi/scsi_scan.c |    2 -
 drivers/scsi/sd.c        |    1 
 6 files changed, 115 insertions(+), 30 deletions(-)

diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index c8bd092fc945..02832d64d918 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -263,6 +263,9 @@ config SCSI_SCAN_ASYNC
 	  You can override this choice by specifying "scsi_mod.scan=sync"
 	  or async on the kernel's command line.
 
+	  Note that this setting also affects whether resuming from
+	  system suspend will be performed asynchronously.
+
 menu "SCSI Transports"
 	depends on SCSI
 
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index d8afec8317cf..1b345bf41a91 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -91,6 +91,15 @@ EXPORT_SYMBOL(scsi_logging_level);
 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()
+ */
+ASYNC_DOMAIN_EXCLUSIVE(scsi_sd_pm_domain);
+EXPORT_SYMBOL(scsi_sd_pm_domain);
+
 /* NB: These are exposed through /proc/scsi/scsi and form part of the ABI.
  * You may not alter any existing entry (although adding new ones is
  * encouraged once assigned by ANSI/INCITS T10
diff --git a/drivers/scsi/scsi_pm.c b/drivers/scsi/scsi_pm.c
index 001e9ceda4c3..7454498c4091 100644
--- a/drivers/scsi/scsi_pm.c
+++ b/drivers/scsi/scsi_pm.c
@@ -18,35 +18,77 @@
 
 #ifdef CONFIG_PM_SLEEP
 
-static int scsi_dev_type_suspend(struct device *dev, int (*cb)(struct device *))
+static int do_scsi_suspend(struct device *dev, const struct dev_pm_ops *pm)
 {
+	return pm && pm->suspend ? pm->suspend(dev) : 0;
+}
+
+static int do_scsi_freeze(struct device *dev, const struct dev_pm_ops *pm)
+{
+	return pm && pm->freeze ? pm->freeze(dev) : 0;
+}
+
+static int do_scsi_poweroff(struct device *dev, const struct dev_pm_ops *pm)
+{
+	return pm && pm->poweroff ? pm->poweroff(dev) : 0;
+}
+
+static int do_scsi_resume(struct device *dev, const struct dev_pm_ops *pm)
+{
+	return pm && pm->resume ? pm->resume(dev) : 0;
+}
+
+static int do_scsi_thaw(struct device *dev, const struct dev_pm_ops *pm)
+{
+	return pm && pm->thaw ? pm->thaw(dev) : 0;
+}
+
+static int do_scsi_restore(struct device *dev, const struct dev_pm_ops *pm)
+{
+	return pm && pm->restore ? pm->restore(dev) : 0;
+}
+
+static int scsi_dev_type_suspend(struct device *dev,
+		int (*cb)(struct device *, const struct dev_pm_ops *))
+{
+	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 	int err;
 
+	/* flush pending in-flight resume operations, suspend is synchronous */
+	async_synchronize_full_domain(&scsi_sd_pm_domain);
+
 	err = scsi_device_quiesce(to_scsi_device(dev));
 	if (err == 0) {
-		if (cb) {
-			err = cb(dev);
-			if (err)
-				scsi_device_resume(to_scsi_device(dev));
-		}
+		err = cb(dev, pm);
+		if (err)
+			scsi_device_resume(to_scsi_device(dev));
 	}
 	dev_dbg(dev, "scsi suspend: %d\n", err);
 	return err;
 }
 
-static int scsi_dev_type_resume(struct device *dev, int (*cb)(struct device *))
+static int scsi_dev_type_resume(struct device *dev,
+		int (*cb)(struct device *, const struct dev_pm_ops *))
 {
+	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
 	int err = 0;
 
-	if (cb)
-		err = cb(dev);
+	err = cb(dev, pm);
 	scsi_device_resume(to_scsi_device(dev));
 	dev_dbg(dev, "scsi resume: %d\n", err);
+
+	if (err == 0) {
+		pm_runtime_disable(dev);
+		pm_runtime_set_active(dev);
+		pm_runtime_enable(dev);
+	}
+
 	return err;
 }
 
 static int
-scsi_bus_suspend_common(struct device *dev, int (*cb)(struct device *))
+scsi_bus_suspend_common(struct device *dev,
+		int (*cb)(struct device *, const struct dev_pm_ops *))
 {
 	int err = 0;
 
@@ -66,20 +108,54 @@ scsi_bus_suspend_common(struct device *dev, int (*cb)(struct device *))
 	return err;
 }
 
-static int
-scsi_bus_resume_common(struct device *dev, int (*cb)(struct device *))
+static void async_sdev_resume(void *dev, async_cookie_t cookie)
 {
-	int err = 0;
+	scsi_dev_type_resume(dev, do_scsi_resume);
+}
 
-	if (scsi_is_sdev_device(dev))
-		err = scsi_dev_type_resume(dev, cb);
+static void async_sdev_thaw(void *dev, async_cookie_t cookie)
+{
+	scsi_dev_type_resume(dev, do_scsi_thaw);
+}
 
-	if (err == 0) {
+static void async_sdev_restore(void *dev, async_cookie_t cookie)
+{
+	scsi_dev_type_resume(dev, do_scsi_restore);
+}
+
+static int scsi_bus_resume_common(struct device *dev,
+		int (*cb)(struct device *, const struct dev_pm_ops *))
+{
+	async_func_t fn;
+
+	if (!scsi_is_sdev_device(dev))
+		fn = NULL;
+	else if (cb == do_scsi_resume)
+		fn = async_sdev_resume;
+	else if (cb == do_scsi_thaw)
+		fn = async_sdev_thaw;
+	else if (cb == do_scsi_restore)
+		fn = async_sdev_restore;
+	else
+		fn = NULL;
+
+	if (fn) {
+		async_schedule_domain(fn, dev, &scsi_sd_pm_domain);
+
+		/*
+		 * If a user has disabled async probing a likely reason
+		 * is due to a storage enclosure that does not inject
+		 * staggered spin-ups.  For safety, make resume
+		 * synchronous as well in that case.
+		 */
+		if (strncmp(scsi_scan_type, "async", 5) != 0)
+			async_synchronize_full_domain(&scsi_sd_pm_domain);
+	} else {
 		pm_runtime_disable(dev);
 		pm_runtime_set_active(dev);
 		pm_runtime_enable(dev);
 	}
-	return err;
+	return 0;
 }
 
 static int scsi_bus_prepare(struct device *dev)
@@ -97,38 +173,32 @@ static int scsi_bus_prepare(struct device *dev)
 
 static int scsi_bus_suspend(struct device *dev)
 {
-	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
-	return scsi_bus_suspend_common(dev, pm ? pm->suspend : NULL);
+	return scsi_bus_suspend_common(dev, do_scsi_suspend);
 }
 
 static int scsi_bus_resume(struct device *dev)
 {
-	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
-	return scsi_bus_resume_common(dev, pm ? pm->resume : NULL);
+	return scsi_bus_resume_common(dev, do_scsi_resume);
 }
 
 static int scsi_bus_freeze(struct device *dev)
 {
-	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
-	return scsi_bus_suspend_common(dev, pm ? pm->freeze : NULL);
+	return scsi_bus_suspend_common(dev, do_scsi_freeze);
 }
 
 static int scsi_bus_thaw(struct device *dev)
 {
-	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
-	return scsi_bus_resume_common(dev, pm ? pm->thaw : NULL);
+	return scsi_bus_resume_common(dev, do_scsi_thaw);
 }
 
 static int scsi_bus_poweroff(struct device *dev)
 {
-	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
-	return scsi_bus_suspend_common(dev, pm ? pm->poweroff : NULL);
+	return scsi_bus_suspend_common(dev, do_scsi_poweroff);
 }
 
 static int scsi_bus_restore(struct device *dev)
 {
-	const struct dev_pm_ops *pm = dev->driver ? dev->driver->pm : NULL;
-	return scsi_bus_resume_common(dev, pm ? pm->restore : NULL);
+	return scsi_bus_resume_common(dev, do_scsi_restore);
 }
 
 #else /* CONFIG_PM_SLEEP */
diff --git a/drivers/scsi/scsi_priv.h b/drivers/scsi/scsi_priv.h
index f079a598bed4..48e5b657e79f 100644
--- a/drivers/scsi/scsi_priv.h
+++ b/drivers/scsi/scsi_priv.h
@@ -112,6 +112,7 @@ extern void scsi_exit_procfs(void);
 #endif /* CONFIG_PROC_FS */
 
 /* scsi_scan.c */
+extern char scsi_scan_type[];
 extern int scsi_complete_async_scans(void);
 extern int scsi_scan_host_selected(struct Scsi_Host *, unsigned int,
 				   unsigned int, unsigned int, int);
@@ -166,6 +167,7 @@ static inline int scsi_autopm_get_host(struct Scsi_Host *h) { return 0; }
 static inline void scsi_autopm_put_host(struct Scsi_Host *h) {}
 #endif /* CONFIG_PM_RUNTIME */
 
+extern struct async_domain scsi_sd_pm_domain;
 extern struct async_domain scsi_sd_probe_domain;
 
 /* 
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 307a81137607..6b2f51f52af6 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -97,7 +97,7 @@ MODULE_PARM_DESC(max_luns,
 #define SCSI_SCAN_TYPE_DEFAULT "sync"
 #endif
 
-static char scsi_scan_type[6] = SCSI_SCAN_TYPE_DEFAULT;
+char scsi_scan_type[6] = SCSI_SCAN_TYPE_DEFAULT;
 
 module_param_string(scan, scsi_scan_type, sizeof(scsi_scan_type), S_IRUGO);
 MODULE_PARM_DESC(scan, "sync, async or none");
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 470954aba728..700c595c603e 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3020,6 +3020,7 @@ static int sd_remove(struct device *dev)
 	devt = disk_devt(sdkp->disk);
 	scsi_autopm_get_device(sdkp->device);
 
+	async_synchronize_full_domain(&scsi_sd_pm_domain);
 	async_synchronize_full_domain(&scsi_sd_probe_domain);
 	blk_queue_prep_rq(sdkp->device->request_queue, scsi_prep_fn);
 	blk_queue_unprep_rq(sdkp->device->request_queue, NULL);