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, 68 insertions, 0 deletions

diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h
new file mode 100644
index 000000000..f27d66fdc
--- /dev/null
+++ b/include/asm-generic/cmpxchg-local.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_CMPXCHG_LOCAL_H
+#define __ASM_GENERIC_CMPXCHG_LOCAL_H
+
+#include <linux/types.h>
+#include <linux/irqflags.h>
+
+extern unsigned long wrong_size_cmpxchg(volatile void *ptr)
+	__noreturn;
+
+/*
+ * Generic version of __cmpxchg_local (disables interrupts). Takes an unsigned
+ * long parameter, supporting various types of architectures.
+ */
+static inline unsigned long __generic_cmpxchg_local(volatile void *ptr,
+		unsigned long old, unsigned long new, int size)
+{
+	unsigned long flags, prev;
+
+	/*
+	 * Sanity checking, compile-time.
+	 */
+	if (size == 8 && sizeof(unsigned long) != 8)
+		wrong_size_cmpxchg(ptr);
+
+	raw_local_irq_save(flags);
+	switch (size) {
+	case 1: prev = *(u8 *)ptr;
+		if (prev == (old & 0xffu))
+			*(u8 *)ptr = (new & 0xffu);
+		break;
+	case 2: prev = *(u16 *)ptr;
+		if (prev == (old & 0xffffu))
+			*(u16 *)ptr = (new & 0xffffu);
+		break;
+	case 4: prev = *(u32 *)ptr;
+		if (prev == (old & 0xffffffffu))
+			*(u32 *)ptr = (new & 0xffffffffu);
+		break;
+	case 8: prev = *(u64 *)ptr;
+		if (prev == old)
+			*(u64 *)ptr = (u64)new;
+		break;
+	default:
+		wrong_size_cmpxchg(ptr);
+	}
+	raw_local_irq_restore(flags);
+	return prev;
+}
+
+/*
+ * Generic version of __cmpxchg64_local. Takes an u64 parameter.
+ */
+static inline u64 __generic_cmpxchg64_local(volatile void *ptr,
+		u64 old, u64 new)
+{
+	u64 prev;
+	unsigned long flags;
+
+	raw_local_irq_save(flags);
+	prev = *(u64 *)ptr;
+	if (prev == old)
+		*(u64 *)ptr = new;
+	raw_local_irq_restore(flags);
+	return prev;
+}
+
+#endif