Merge branches 'expcb.2026.07.24a', 'misc.2026.07.30a', 'rcu-tasks.2026.07.30a', 'srcu.2026.08.11a' and 'torture.2026.08.14a' into HEADgrafted

Changes:

Make expedited grace periods expedite normal RCU callbacks

Miscellaneous fixes:
 * Improve diagnostic output with character task states.
 * Mark accesses to inform KCSAN of concurrency design.
 * Move from kmalloc() to kmalloc_obj().
 * Documentation updates.
 * Improve handling of RCU deferred quiescent states.
 * Clean up unused function arguments and structure fields.
 * Reduce show_rcu_gp_kthreads() stack space.

Tasks RCU updates:
 * Clean up after SRCU re-implementation of Tasks Trace RCU.
 * Mark accesses to inform KCSAN of concurrency design.
 * Add ->lazy_timer status to diagnostic output.
 * Remove an unnecessary memory barrier.
 * Fix a data race, courtesy of KCSAN.
 * Documentation updates.
 * Convert cond_resched_tasks_rcu_qs() from macro to static inline
   function.

SRCU updates:
 * Add Rust helpers for SRCU.
 * Avoid losing queued work at cleanup_srcu_struct() time.

Torture-test updates:
 * Preparation work for immediate RCU priority deboosting.
 * Test RCU readers from real interrupt handlers (as opposed to softirq).
 * Simplify code through use of cpumask_next_wrap().
 * Improve diagnostic output with character task states.
 * Add rcutorture.nwriters parameter to allow lightweight stall testing,
   and rcutorture.stall_only to make doing so easier.
 * Test an RCU Tasks Trace grace period implying an RCU grace period.
 * Make RCU Tasks Trace torturing track reader batches.
 * Fix a data race, courtesy of KCSAN.
 * Plug a shuffle_tmp_mask memory leak on kthread spawn failure.

1 files changed, 124 insertions, 0 deletions

diff --git a/include/drm/spsc_queue.h b/include/drm/spsc_queue.h
new file mode 100644
index 000000000..ee9df8cc6
--- /dev/null
+++ b/include/drm/spsc_queue.h
@@ -0,0 +1,124 @@
+/*
+ * Copyright 2017 Advanced Micro Devices, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+#ifndef DRM_SCHEDULER_SPSC_QUEUE_H_
+#define DRM_SCHEDULER_SPSC_QUEUE_H_
+
+#include <linux/atomic.h>
+#include <linux/preempt.h>
+
+/** SPSC lockless queue */
+
+struct spsc_node {
+
+	/* Stores spsc_node* */
+	struct spsc_node *next;
+};
+
+struct spsc_queue {
+
+	 struct spsc_node *head;
+
+	/* atomic pointer to struct spsc_node* */
+	atomic_long_t tail;
+
+	atomic_t job_count;
+};
+
+static inline void spsc_queue_init(struct spsc_queue *queue)
+{
+	queue->head = NULL;
+	atomic_long_set(&queue->tail, (long)&queue->head);
+	atomic_set(&queue->job_count, 0);
+}
+
+static inline struct spsc_node *spsc_queue_peek(struct spsc_queue *queue)
+{
+	return queue->head;
+}
+
+static inline int spsc_queue_count(struct spsc_queue *queue)
+{
+	return atomic_read(&queue->job_count);
+}
+
+static inline bool spsc_queue_push(struct spsc_queue *queue, struct spsc_node *node)
+{
+	struct spsc_node **tail;
+
+	node->next = NULL;
+
+	preempt_disable();
+
+	atomic_inc(&queue->job_count);
+	smp_mb__after_atomic();
+
+	tail = (struct spsc_node **)atomic_long_xchg(&queue->tail, (long)&node->next);
+	WRITE_ONCE(*tail, node);
+
+	/*
+	 * In case of first element verify new node will be visible to the consumer
+	 * thread when we ping the kernel thread that there is new work to do.
+	 */
+	smp_wmb();
+
+	preempt_enable();
+
+	return tail == &queue->head;
+}
+
+
+static inline struct spsc_node *spsc_queue_pop(struct spsc_queue *queue)
+{
+	struct spsc_node *next, *node;
+
+	/* Verify reading from memory and not the cache */
+	smp_rmb();
+
+	node = READ_ONCE(queue->head);
+
+	if (!node)
+		return NULL;
+
+	next = READ_ONCE(node->next);
+	WRITE_ONCE(queue->head, next);
+
+	if (unlikely(!next)) {
+		/* slowpath for the last element in the queue */
+
+		if (atomic_long_cmpxchg(&queue->tail,
+				(long)&node->next, (long) &queue->head) != (long)&node->next) {
+			/* Updating tail failed wait for new next to appear */
+			do {
+				smp_rmb();
+			} while (unlikely(!(queue->head = READ_ONCE(node->next))));
+		}
+	}
+
+	atomic_dec(&queue->job_count);
+	return node;
+}
+
+
+
+#endif /* DRM_SCHEDULER_SPSC_QUEUE_H_ */