[PATCH 1/3] driver core: enable drivers to use deferred probe from init

[Luis R. Rodriguez]

From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>

Tetsuo bisected and found that commit 786235ee "kthread: make
kthread_create() killable" modified kthread_create() to bail as
soon as SIGKILL is received. This is causing some issues with
some drivers and at times boot. Joseph then found that failures
occur as the systemd-udevd process sends SIGKILL to modprobe if
probe on a driver takes over 30 seconds. When this happens probe
will fail on any driver, its why booting on some system will fail
if the driver happens to be a storage related driver. Some folks
have suggested fixing this by modifying kthread_create() to not
leave upon SIGKILL [3], upon review Oleg rejected this change and
the discussion was punted out to systemd to see if the default
timeout could be increased from 30 seconds to 120. The opinion of
the systemd maintainers is that the driver's behavior should
be fixed [4]. Linus seems to agree [5], however more recently even
networking drivers have been reported to fail on probe since just
writing the firmware to a device and kicking it can take easy over
60 seconds [6]. Benjamim was able to trace the issues recently
reported on cxgb4 down to the same systemd-udevd 30 second timeout [6].

This is an alternative solution which enables drivers that are
known to take long to use deferred probe workqueue. This avoids
the 30 second timeout and lets us annotate drivers with long
init sequences.

As drivers determine a component is not yet available and needs
to defer probe you'll be notified this happen upon init for each
device but now with a message such as:

pci 0000:03:00.0: Driver cxgb4 requests probe deferral on init

You should see one of these per struct device probed.

[0] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1276705
[1] https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1297248
[2] http://lists.freedesktop.org/archives/systemd-devel/2014-March/018006.html
[3] http://thread.gmane.org/gmane.linux.ubuntu.devel.kernel.general/39123
[4] http://article.gmane.org/gmane.comp.sysutils.systemd.devel/17860
[5] http://article.gmane.org/gmane.linux.kernel/1671333
[6] https://bugzilla.novell.com/show_bug.cgi?id=877622

Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>
Cc: Kay Sievers <kay@xxxxxxxx>
Cc: One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx>
Cc: Tim Gardner <tim.gardner@xxxxxxxxxxxxx>
Cc: Pierre Fersing <pierre-fersing@xxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Benjamin Poirier <bpoirier@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Nagalakshmi Nandigama <nagalakshmi.nandigama@xxxxxxxxxxxxx>
Cc: Praveen Krishnamoorthy <praveen.krishnamoorthy@xxxxxxxxxxxxx>
Cc: Sreekanth Reddy <sreekanth.reddy@xxxxxxxxxxxxx>
Cc: Abhijit Mahajan <abhijit.mahajan@xxxxxxxxxxxxx>
Cc: Hariprasad S <hariprasad@xxxxxxxxxxx>
Cc: Santosh Rastapur <santosh@xxxxxxxxxxx>
Cc: MPT-FusionLinux.pdl@xxxxxxxxxxxxx
Cc: linux-scsi@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>
---
 drivers/base/dd.c      | 15 ++++++++++++++-
 include/linux/device.h | 12 ++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index e4ffbcf..7a271dc 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -374,6 +374,19 @@ void wait_for_device_probe(void)
 }
 EXPORT_SYMBOL_GPL(wait_for_device_probe);
 
+static int __driver_probe_device(struct device_driver *drv, struct device *dev)
+{
+	if (drv->delay_probe && !dev->init_delayed_probe) {
+		dev_info(dev, "Driver %s requests probe deferral on init\n",
+			 drv->name);
+		dev->init_delayed_probe = true;
+		driver_deferred_probe_add(dev);
+		return -EPROBE_DEFER;
+	}
+
+	return really_probe(dev, drv);
+}
+
 /**
  * driver_probe_device - attempt to bind device & driver together
  * @drv: driver to bind a device to
@@ -396,7 +409,7 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
 		 drv->bus->name, __func__, dev_name(dev), drv->name);
 
 	pm_runtime_barrier(dev);
-	ret = really_probe(dev, drv);
+	ret = __driver_probe_device(drv, dev);
 	pm_request_idle(dev);
 
 	return ret;
diff --git a/include/linux/device.h b/include/linux/device.h
index af424ac..11da1b7 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -200,6 +200,12 @@ extern struct klist *bus_get_device_klist(struct bus_type *bus);
  * @owner:	The module owner.
  * @mod_name:	Used for built-in modules.
  * @suppress_bind_attrs: Disables bind/unbind via sysfs.
+ * @delay_probe: this driver is requesting a deferred probe since
+ *	initialization. This can be desirable if its known the device probe
+ *	or initialization takes more than 30 seconds.
+ * @delayed_probe_devs: devices which have gone through a delayed probe. This
+ * 	is used internally by the driver core to keep track of which devices
+ * 	have gone through a delayed probe.
  * @of_match_table: The open firmware table.
  * @acpi_match_table: The ACPI match table.
  * @probe:	Called to query the existence of a specific device,
@@ -234,6 +240,9 @@ struct device_driver {
 
 	bool suppress_bind_attrs;	/* disables bind/unbind via sysfs */
 
+	bool delay_probe;		/* requests deferred probe */
+	struct list_head delayed_probe_devs;
+
 	const struct of_device_id	*of_match_table;
 	const struct acpi_device_id	*acpi_match_table;
 
@@ -715,6 +724,8 @@ struct acpi_dev_node {
  *
  * @offline_disabled: If set, the device is permanently online.
  * @offline:	Set after successful invocation of bus type's .offline().
+ * @init_delayed_probe: lets the coore keep track if the device has already
+ * 	gone through a delayed probe upon init.
  *
  * At the lowest level, every device in a Linux system is represented by an
  * instance of struct device. The device structure contains the information
@@ -793,6 +804,7 @@ struct device {
 
 	bool			offline_disabled:1;
 	bool			offline:1;
+	bool			init_delayed_probe:1;
 };
 
 static inline struct device *kobj_to_dev(struct kobject *kobj)
-- 
2.0.1

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