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, 319 insertions, 0 deletions

diff --git a/drivers/scsi/arm/queue.c b/drivers/scsi/arm/queue.c
new file mode 100644
index 000000000..797cf4971
--- /dev/null
+++ b/drivers/scsi/arm/queue.c
@@ -0,0 +1,319 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/drivers/acorn/scsi/queue.c: queue handling primitives
+ *
+ *  Copyright (C) 1997-2000 Russell King
+ *
+ *  Changelog:
+ *   15-Sep-1997 RMK	Created.
+ *   11-Oct-1997 RMK	Corrected problem with queue_remove_exclude
+ *			not updating internal linked list properly
+ *			(was causing commands to go missing).
+ *   30-Aug-2000 RMK	Use Linux list handling and spinlocks
+ */
+#include <linux/module.h>
+#include <linux/blkdev.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/list.h>
+#include <linux/init.h>
+
+#include <scsi/scsi.h>
+#include <scsi/scsi_cmnd.h>
+#include <scsi/scsi_device.h>
+#include <scsi/scsi_eh.h>
+#include <scsi/scsi_tcq.h>
+
+#define DEBUG
+
+typedef struct queue_entry {
+	struct list_head   list;
+	struct scsi_cmnd   *SCpnt;
+#ifdef DEBUG
+	unsigned long	   magic;
+#endif
+} QE_t;
+
+#ifdef DEBUG
+#define QUEUE_MAGIC_FREE	0xf7e1c9a3
+#define QUEUE_MAGIC_USED	0xf7e1cc33
+
+#define SET_MAGIC(q,m)	((q)->magic = (m))
+#define BAD_MAGIC(q,m)	((q)->magic != (m))
+#else
+#define SET_MAGIC(q,m)	do { } while (0)
+#define BAD_MAGIC(q,m)	(0)
+#endif
+
+#include "queue.h"
+
+#define NR_QE	32
+
+/*
+ * Function: void queue_initialise (Queue_t *queue)
+ * Purpose : initialise a queue
+ * Params  : queue - queue to initialise
+ */
+int queue_initialise (Queue_t *queue)
+{
+	unsigned int nqueues = NR_QE;
+	QE_t *q;
+
+	spin_lock_init(&queue->queue_lock);
+	INIT_LIST_HEAD(&queue->head);
+	INIT_LIST_HEAD(&queue->free);
+
+	/*
+	 * If life was easier, then SCpnt would have a
+	 * host-available list head, and we wouldn't
+	 * need to keep free lists or allocate this
+	 * memory.
+	 */
+	queue->alloc = q = kmalloc_objs(QE_t, nqueues);
+	if (q) {
+		for (; nqueues; q++, nqueues--) {
+			SET_MAGIC(q, QUEUE_MAGIC_FREE);
+			q->SCpnt = NULL;
+			list_add(&q->list, &queue->free);
+		}
+	}
+
+	return queue->alloc != NULL;
+}
+
+/*
+ * Function: void queue_free (Queue_t *queue)
+ * Purpose : free a queue
+ * Params  : queue - queue to free
+ */
+void queue_free (Queue_t *queue)
+{
+	if (!list_empty(&queue->head))
+		printk(KERN_WARNING "freeing non-empty queue %p\n", queue);
+	kfree(queue->alloc);
+}
+     
+
+/*
+ * Function: int __queue_add(Queue_t *queue, struct scsi_cmnd *SCpnt, int head)
+ * Purpose : Add a new command onto a queue, adding REQUEST_SENSE to head.
+ * Params  : queue - destination queue
+ *	     SCpnt - command to add
+ *	     head  - add command to head of queue
+ * Returns : 0 on error, !0 on success
+ */
+int __queue_add(Queue_t *queue, struct scsi_cmnd *SCpnt, int head)
+{
+	unsigned long flags;
+	struct list_head *l;
+	QE_t *q;
+	int ret = 0;
+
+	spin_lock_irqsave(&queue->queue_lock, flags);
+	if (list_empty(&queue->free))
+		goto empty;
+
+	l = queue->free.next;
+	list_del(l);
+
+	q = list_entry(l, QE_t, list);
+	BUG_ON(BAD_MAGIC(q, QUEUE_MAGIC_FREE));
+
+	SET_MAGIC(q, QUEUE_MAGIC_USED);
+	q->SCpnt = SCpnt;
+
+	if (head)
+		list_add(l, &queue->head);
+	else
+		list_add_tail(l, &queue->head);
+
+	ret = 1;
+empty:
+	spin_unlock_irqrestore(&queue->queue_lock, flags);
+	return ret;
+}
+
+static struct scsi_cmnd *__queue_remove(Queue_t *queue, struct list_head *ent)
+{
+	QE_t *q;
+
+	/*
+	 * Move the entry from the "used" list onto the "free" list
+	 */
+	list_del(ent);
+	q = list_entry(ent, QE_t, list);
+	BUG_ON(BAD_MAGIC(q, QUEUE_MAGIC_USED));
+
+	SET_MAGIC(q, QUEUE_MAGIC_FREE);
+	list_add(ent, &queue->free);
+
+	return q->SCpnt;
+}
+
+/*
+ * Function: struct scsi_cmnd *queue_remove_exclude (queue, exclude)
+ * Purpose : remove a SCSI command from a queue
+ * Params  : queue   - queue to remove command from
+ *	     exclude - bit array of target&lun which is busy
+ * Returns : struct scsi_cmnd if successful (and a reference), or NULL if no command available
+ */
+struct scsi_cmnd *queue_remove_exclude(Queue_t *queue, unsigned long *exclude)
+{
+	unsigned long flags;
+	struct list_head *l;
+	struct scsi_cmnd *SCpnt = NULL;
+
+	spin_lock_irqsave(&queue->queue_lock, flags);
+	list_for_each(l, &queue->head) {
+		QE_t *q = list_entry(l, QE_t, list);
+		if (!test_bit(q->SCpnt->device->id * 8 +
+			      (u8)(q->SCpnt->device->lun & 0x7), exclude)) {
+			SCpnt = __queue_remove(queue, l);
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&queue->queue_lock, flags);
+
+	return SCpnt;
+}
+
+/*
+ * Function: struct scsi_cmnd *queue_remove (queue)
+ * Purpose : removes first SCSI command from a queue
+ * Params  : queue   - queue to remove command from
+ * Returns : struct scsi_cmnd if successful (and a reference), or NULL if no command available
+ */
+struct scsi_cmnd *queue_remove(Queue_t *queue)
+{
+	unsigned long flags;
+	struct scsi_cmnd *SCpnt = NULL;
+
+	spin_lock_irqsave(&queue->queue_lock, flags);
+	if (!list_empty(&queue->head))
+		SCpnt = __queue_remove(queue, queue->head.next);
+	spin_unlock_irqrestore(&queue->queue_lock, flags);
+
+	return SCpnt;
+}
+
+/*
+ * Function: struct scsi_cmnd *queue_remove_tgtluntag (queue, target, lun, tag)
+ * Purpose : remove a SCSI command from the queue for a specified target/lun/tag
+ * Params  : queue  - queue to remove command from
+ *	     target - target that we want
+ *	     lun    - lun on device
+ *	     tag    - tag on device
+ * Returns : struct scsi_cmnd if successful, or NULL if no command satisfies requirements
+ */
+struct scsi_cmnd *queue_remove_tgtluntag(Queue_t *queue, int target, int lun,
+					 int tag)
+{
+	unsigned long flags;
+	struct list_head *l;
+	struct scsi_cmnd *SCpnt = NULL;
+
+	spin_lock_irqsave(&queue->queue_lock, flags);
+	list_for_each(l, &queue->head) {
+		QE_t *q = list_entry(l, QE_t, list);
+		if (q->SCpnt->device->id == target && q->SCpnt->device->lun == lun &&
+		    scsi_cmd_to_rq(q->SCpnt)->tag == tag) {
+			SCpnt = __queue_remove(queue, l);
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&queue->queue_lock, flags);
+
+	return SCpnt;
+}
+
+/*
+ * Function: queue_remove_all_target(queue, target)
+ * Purpose : remove all SCSI commands from the queue for a specified target
+ * Params  : queue  - queue to remove command from
+ *           target - target device id
+ * Returns : nothing
+ */
+void queue_remove_all_target(Queue_t *queue, int target)
+{
+	unsigned long flags;
+	struct list_head *l;
+
+	spin_lock_irqsave(&queue->queue_lock, flags);
+	list_for_each(l, &queue->head) {
+		QE_t *q = list_entry(l, QE_t, list);
+		if (q->SCpnt->device->id == target)
+			__queue_remove(queue, l);
+	}
+	spin_unlock_irqrestore(&queue->queue_lock, flags);
+}
+
+/*
+ * Function: int queue_probetgtlun (queue, target, lun)
+ * Purpose : check to see if we have a command in the queue for the specified
+ *	     target/lun.
+ * Params  : queue  - queue to look in
+ *	     target - target we want to probe
+ *	     lun    - lun on target
+ * Returns : 0 if not found, != 0 if found
+ */
+int queue_probetgtlun (Queue_t *queue, int target, int lun)
+{
+	unsigned long flags;
+	struct list_head *l;
+	int found = 0;
+
+	spin_lock_irqsave(&queue->queue_lock, flags);
+	list_for_each(l, &queue->head) {
+		QE_t *q = list_entry(l, QE_t, list);
+		if (q->SCpnt->device->id == target && q->SCpnt->device->lun == lun) {
+			found = 1;
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&queue->queue_lock, flags);
+
+	return found;
+}
+
+/*
+ * Function: int queue_remove_cmd(Queue_t *queue, struct scsi_cmnd *SCpnt)
+ * Purpose : remove a specific command from the queues
+ * Params  : queue - queue to look in
+ *	     SCpnt - command to find
+ * Returns : 0 if not found
+ */
+int queue_remove_cmd(Queue_t *queue, struct scsi_cmnd *SCpnt)
+{
+	unsigned long flags;
+	struct list_head *l;
+	int found = 0;
+
+	spin_lock_irqsave(&queue->queue_lock, flags);
+	list_for_each(l, &queue->head) {
+		QE_t *q = list_entry(l, QE_t, list);
+		if (q->SCpnt == SCpnt) {
+			__queue_remove(queue, l);
+			found = 1;
+			break;
+		}
+	}
+	spin_unlock_irqrestore(&queue->queue_lock, flags);
+
+	return found;
+}
+
+EXPORT_SYMBOL(queue_initialise);
+EXPORT_SYMBOL(queue_free);
+EXPORT_SYMBOL(__queue_add);
+EXPORT_SYMBOL(queue_remove);
+EXPORT_SYMBOL(queue_remove_exclude);
+EXPORT_SYMBOL(queue_remove_tgtluntag);
+EXPORT_SYMBOL(queue_remove_cmd);
+EXPORT_SYMBOL(queue_remove_all_target);
+EXPORT_SYMBOL(queue_probetgtlun);
+
+MODULE_AUTHOR("Russell King");
+MODULE_DESCRIPTION("SCSI command queueing");
+MODULE_LICENSE("GPL");