Merge branch 'writeback-workqueue' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq into for-3.10/core

Tejun writes:

-----

This is the pull request for the earlier patchset[1] with the same
name.  It's only three patches (the first one was committed to
workqueue tree) but the merge strategy is a bit involved due to the
dependencies.

* Because the conversion needs features from wq/for-3.10,
  block/for-3.10/core is based on rc3, and wq/for-3.10 has conflicts
  with rc3, I pulled mainline (rc5) into wq/for-3.10 to prevent those
  workqueue conflicts from flaring up in block tree.

* Resolving the issue that Jan and Dave raised about debugging
  requires arch-wide changes.  The patchset is being worked on[2] but
  it'll have to go through -mm after these changes show up in -next,
  and not included in this pull request.

The three commits are located in the following git branch.

  git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git writeback-workqueue

Pulling it into block/for-3.10/core produces a conflict in
drivers/md/raid5.c between the following two commits.

  e3620a3ad5 ("MD RAID5: Avoid accessing gendisk or queue structs when not available")
  2f6db2a707 ("raid5: use bio_reset()")

The conflict is trivial - one removes an "if ()" conditional while the
other removes "rbi->bi_next = NULL" right above it.  We just need to
remove both.  The merged branch is available at

  git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git block-test-merge

so that you can use it for verification.  The test merge commit has
proper merge description.

While these changes are a bit of pain to route, they make code simpler
and even have, while minute, measureable performance gain[3] even on a
workload which isn't particularly favorable to showing the benefits of
this conversion.

----

Fixed up the conflict.

Conflicts:
	drivers/md/raid5.c

Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 52 insertions, 21 deletions

diff --git a/drivers/base/bus.c b/drivers/base/bus.c
index 519865b53f76..2ae2d2f92b6b 100644
--- a/drivers/base/bus.c
+++ b/drivers/base/bus.c
@@ -1205,26 +1205,10 @@ static void system_root_device_release(struct device *dev)
 {
 	kfree(dev);
 }
-/**
- * subsys_system_register - register a subsystem at /sys/devices/system/
- * @subsys: system subsystem
- * @groups: default attributes for the root device
- *
- * All 'system' subsystems have a /sys/devices/system/<name> root device
- * with the name of the subsystem. The root device can carry subsystem-
- * wide attributes. All registered devices are below this single root
- * device and are named after the subsystem with a simple enumeration
- * number appended. The registered devices are not explicitely named;
- * only 'id' in the device needs to be set.
- *
- * Do not use this interface for anything new, it exists for compatibility
- * with bad ideas only. New subsystems should use plain subsystems; and
- * add the subsystem-wide attributes should be added to the subsystem
- * directory itself and not some create fake root-device placed in
- * /sys/devices/system/<name>.
- */
-int subsys_system_register(struct bus_type *subsys,
-			   const struct attribute_group **groups)
+
+static int subsys_register(struct bus_type *subsys,
+			   const struct attribute_group **groups,
+			   struct kobject *parent_of_root)
 {
 	struct device *dev;
 	int err;
@@ -1243,7 +1227,7 @@ int subsys_system_register(struct bus_type *subsys,
 	if (err < 0)
 		goto err_name;
 
-	dev->kobj.parent = &system_kset->kobj;
+	dev->kobj.parent = parent_of_root;
 	dev->groups = groups;
 	dev->release = system_root_device_release;
 
@@ -1263,8 +1247,55 @@ err_dev:
 	bus_unregister(subsys);
 	return err;
 }
+
+/**
+ * subsys_system_register - register a subsystem at /sys/devices/system/
+ * @subsys: system subsystem
+ * @groups: default attributes for the root device
+ *
+ * All 'system' subsystems have a /sys/devices/system/<name> root device
+ * with the name of the subsystem. The root device can carry subsystem-
+ * wide attributes. All registered devices are below this single root
+ * device and are named after the subsystem with a simple enumeration
+ * number appended. The registered devices are not explicitely named;
+ * only 'id' in the device needs to be set.
+ *
+ * Do not use this interface for anything new, it exists for compatibility
+ * with bad ideas only. New subsystems should use plain subsystems; and
+ * add the subsystem-wide attributes should be added to the subsystem
+ * directory itself and not some create fake root-device placed in
+ * /sys/devices/system/<name>.
+ */
+int subsys_system_register(struct bus_type *subsys,
+			   const struct attribute_group **groups)
+{
+	return subsys_register(subsys, groups, &system_kset->kobj);
+}
 EXPORT_SYMBOL_GPL(subsys_system_register);
 
+/**
+ * subsys_virtual_register - register a subsystem at /sys/devices/virtual/
+ * @subsys: virtual subsystem
+ * @groups: default attributes for the root device
+ *
+ * All 'virtual' subsystems have a /sys/devices/system/<name> root device
+ * with the name of the subystem.  The root device can carry subsystem-wide
+ * attributes.  All registered devices are below this single root device.
+ * There's no restriction on device naming.  This is for kernel software
+ * constructs which need sysfs interface.
+ */
+int subsys_virtual_register(struct bus_type *subsys,
+			    const struct attribute_group **groups)
+{
+	struct kobject *virtual_dir;
+
+	virtual_dir = virtual_device_parent(NULL);
+	if (!virtual_dir)
+		return -ENOMEM;
+
+	return subsys_register(subsys, groups, virtual_dir);
+}
+
 int __init buses_init(void)
 {
 	bus_kset = kset_create_and_add("bus", &bus_uevent_ops, NULL);