sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 267 insertions, 0 deletions

diff --git a/drivers/scsi/raid_class.c b/drivers/scsi/raid_class.c
new file mode 100644
index 000000000..94f76e358
--- /dev/null
+++ b/drivers/scsi/raid_class.c
@@ -0,0 +1,267 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * raid_class.c - implementation of a simple raid visualisation class
+ *
+ * Copyright (c) 2005 - James Bottomley <James.Bottomley@steeleye.com>
+ *
+ * This class is designed to allow raid attributes to be visualised and
+ * manipulated in a form independent of the underlying raid.  Ultimately this
+ * should work for both hardware and software raids.
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/raid_class.h>
+#include <scsi/scsi_device.h>
+#include <scsi/scsi_host.h>
+
+#define RAID_NUM_ATTRS	3
+
+struct raid_internal {
+	struct raid_template r;
+	struct raid_function_template *f;
+	/* The actual attributes */
+	struct device_attribute private_attrs[RAID_NUM_ATTRS];
+	/* The array of null terminated pointers to attributes 
+	 * needed by scsi_sysfs.c */
+	struct device_attribute *attrs[RAID_NUM_ATTRS + 1];
+};
+
+struct raid_component {
+	struct list_head node;
+	struct device dev;
+	int num;
+};
+
+#define to_raid_internal(tmpl)	container_of(tmpl, struct raid_internal, r)
+
+#define tc_to_raid_internal(tcont) ({					\
+	struct raid_template *r =					\
+		container_of(tcont, struct raid_template, raid_attrs);	\
+	to_raid_internal(r);						\
+})
+
+#define ac_to_raid_internal(acont) ({					\
+	struct transport_container *tc =				\
+		container_of(acont, struct transport_container, ac);	\
+	tc_to_raid_internal(tc);					\
+})
+
+#define device_to_raid_internal(dev) ({				\
+	struct attribute_container *ac =				\
+		attribute_container_classdev_to_container(dev);	\
+	ac_to_raid_internal(ac);					\
+})
+	
+
+static int raid_match(struct attribute_container *cont, struct device *dev)
+{
+	/* We have to look for every subsystem that could house
+	 * emulated RAID devices, so start with SCSI */
+	struct raid_internal *i = ac_to_raid_internal(cont);
+
+	if (IS_ENABLED(CONFIG_SCSI) && scsi_is_sdev_device(dev)) {
+		struct scsi_device *sdev = to_scsi_device(dev);
+
+		if (i->f->cookie != sdev->host->hostt)
+			return 0;
+
+		return i->f->is_raid(dev);
+	}
+	/* FIXME: look at other subsystems too */
+	return 0;
+}
+
+static int raid_setup(struct transport_container *tc, struct device *dev,
+		       struct device *cdev)
+{
+	struct raid_data *rd;
+
+	BUG_ON(dev_get_drvdata(cdev));
+
+	rd = kzalloc_obj(*rd);
+	if (!rd)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&rd->component_list);
+	dev_set_drvdata(cdev, rd);
+		
+	return 0;
+}
+
+static int raid_remove(struct transport_container *tc, struct device *dev,
+		       struct device *cdev)
+{
+	struct raid_data *rd = dev_get_drvdata(cdev);
+	struct raid_component *rc, *next;
+	dev_printk(KERN_ERR, dev, "RAID REMOVE\n");
+	dev_set_drvdata(cdev, NULL);
+	list_for_each_entry_safe(rc, next, &rd->component_list, node) {
+		list_del(&rc->node);
+		dev_printk(KERN_ERR, rc->dev.parent, "RAID COMPONENT REMOVE\n");
+		device_unregister(&rc->dev);
+	}
+	dev_printk(KERN_ERR, dev, "RAID REMOVE DONE\n");
+	kfree(rd);
+	return 0;
+}
+
+static DECLARE_TRANSPORT_CLASS(raid_class,
+			       "raid_devices",
+			       raid_setup,
+			       raid_remove,
+			       NULL);
+
+static const struct {
+	enum raid_state	value;
+	char		*name;
+} raid_states[] = {
+	{ RAID_STATE_UNKNOWN, "unknown" },
+	{ RAID_STATE_ACTIVE, "active" },
+	{ RAID_STATE_DEGRADED, "degraded" },
+	{ RAID_STATE_RESYNCING, "resyncing" },
+	{ RAID_STATE_OFFLINE, "offline" },
+};
+
+static const char *raid_state_name(enum raid_state state)
+{
+	int i;
+	char *name = NULL;
+
+	for (i = 0; i < ARRAY_SIZE(raid_states); i++) {
+		if (raid_states[i].value == state) {
+			name = raid_states[i].name;
+			break;
+		}
+	}
+	return name;
+}
+
+static struct {
+	enum raid_level value;
+	char *name;
+} raid_levels[] = {
+	{ RAID_LEVEL_UNKNOWN, "unknown" },
+	{ RAID_LEVEL_LINEAR, "linear" },
+	{ RAID_LEVEL_0, "raid0" },
+	{ RAID_LEVEL_1, "raid1" },
+	{ RAID_LEVEL_10, "raid10" },
+	{ RAID_LEVEL_1E, "raid1e" },
+	{ RAID_LEVEL_3, "raid3" },
+	{ RAID_LEVEL_4, "raid4" },
+	{ RAID_LEVEL_5, "raid5" },
+	{ RAID_LEVEL_50, "raid50" },
+	{ RAID_LEVEL_6, "raid6" },
+	{ RAID_LEVEL_JBOD, "jbod" },
+};
+
+static const char *raid_level_name(enum raid_level level)
+{
+	int i;
+	char *name = NULL;
+
+	for (i = 0; i < ARRAY_SIZE(raid_levels); i++) {
+		if (raid_levels[i].value == level) {
+			name = raid_levels[i].name;
+			break;
+		}
+	}
+	return name;
+}
+
+#define raid_attr_show_internal(attr, fmt, var, code)			\
+static ssize_t raid_show_##attr(struct device *dev, 			\
+				struct device_attribute *attr, 		\
+				char *buf)				\
+{									\
+	struct raid_data *rd = dev_get_drvdata(dev);			\
+	code								\
+	return snprintf(buf, 20, #fmt "\n", var);			\
+}
+
+#define raid_attr_ro_states(attr, states, code)				\
+raid_attr_show_internal(attr, %s, name,					\
+	const char *name;						\
+	code								\
+	name = raid_##states##_name(rd->attr);				\
+)									\
+static DEVICE_ATTR(attr, S_IRUGO, raid_show_##attr, NULL)
+
+
+#define raid_attr_ro_internal(attr, code)				\
+raid_attr_show_internal(attr, %d, rd->attr, code)			\
+static DEVICE_ATTR(attr, S_IRUGO, raid_show_##attr, NULL)
+
+#define ATTR_CODE(attr)							\
+	struct raid_internal *i = device_to_raid_internal(dev);		\
+	if (i->f->get_##attr)						\
+		i->f->get_##attr(dev->parent);
+
+#define raid_attr_ro(attr)	raid_attr_ro_internal(attr, )
+#define raid_attr_ro_fn(attr)	raid_attr_ro_internal(attr, ATTR_CODE(attr))
+#define raid_attr_ro_state(attr)	raid_attr_ro_states(attr, attr, )
+#define raid_attr_ro_state_fn(attr)	raid_attr_ro_states(attr, attr, ATTR_CODE(attr))
+
+
+raid_attr_ro_state(level);
+raid_attr_ro_fn(resync);
+raid_attr_ro_state_fn(state);
+
+struct raid_template *
+raid_class_attach(struct raid_function_template *ft)
+{
+	struct raid_internal *i = kzalloc_obj(struct raid_internal);
+	int count = 0;
+
+	if (unlikely(!i))
+		return NULL;
+
+	i->f = ft;
+
+	i->r.raid_attrs.ac.class = &raid_class.class;
+	i->r.raid_attrs.ac.match = raid_match;
+	i->r.raid_attrs.ac.attrs = &i->attrs[0];
+
+	attribute_container_register(&i->r.raid_attrs.ac);
+
+	i->attrs[count++] = &dev_attr_level;
+	i->attrs[count++] = &dev_attr_resync;
+	i->attrs[count++] = &dev_attr_state;
+
+	i->attrs[count] = NULL;
+	BUG_ON(count > RAID_NUM_ATTRS);
+
+	return &i->r;
+}
+EXPORT_SYMBOL(raid_class_attach);
+
+void
+raid_class_release(struct raid_template *r)
+{
+	struct raid_internal *i = to_raid_internal(r);
+
+	BUG_ON(attribute_container_unregister(&i->r.raid_attrs.ac));
+
+	kfree(i);
+}
+EXPORT_SYMBOL(raid_class_release);
+
+static __init int raid_init(void)
+{
+	return transport_class_register(&raid_class);
+}
+
+static __exit void raid_exit(void)
+{
+	transport_class_unregister(&raid_class);
+}
+
+MODULE_AUTHOR("James Bottomley");
+MODULE_DESCRIPTION("RAID device class");
+MODULE_LICENSE("GPL");
+
+module_init(raid_init);
+module_exit(raid_exit);
+