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/arch/alpha/boot/head.S b/arch/alpha/boot/head.S
new file mode 100644
index 000000000..06a7c95fe
--- /dev/null
+++ b/arch/alpha/boot/head.S
@@ -0,0 +1,124 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * arch/alpha/boot/head.S
+ *
+ * initial bootloader stuff..
+ */
+
+#include <asm/pal.h>
+
+	.set noreorder
+	.globl	__start
+	.ent	__start
+__start:
+	br	$29,2f
+2:	ldgp	$29,0($29)
+	jsr	$26,start_kernel
+	call_pal PAL_halt
+	.end __start
+
+	.align 5
+	.globl	wrent
+	.ent	wrent
+wrent:
+	.prologue 0
+	call_pal PAL_wrent
+	ret ($26)
+	.end wrent
+
+	.align 5
+	.globl	wrkgp
+	.ent	wrkgp
+wrkgp:
+	.prologue 0
+	call_pal PAL_wrkgp
+	ret ($26)
+	.end wrkgp
+
+	.align 5
+	.globl	switch_to_osf_pal
+	.ent	switch_to_osf_pal
+switch_to_osf_pal:
+	subq	$30,128,$30
+	.frame	$30,128,$26
+	stq	$26,0($30)
+	stq	$1,8($30)
+	stq	$2,16($30)
+	stq	$3,24($30)
+	stq	$4,32($30)
+	stq	$5,40($30)
+	stq	$6,48($30)
+	stq	$7,56($30)
+	stq	$8,64($30)
+	stq	$9,72($30)
+	stq	$10,80($30)
+	stq	$11,88($30)
+	stq	$12,96($30)
+	stq	$13,104($30)
+	stq	$14,112($30)
+	stq	$15,120($30)
+	.prologue 0
+
+	stq	$30,0($17)	/* save KSP in PCB */
+
+	bis	$30,$30,$20	/* a4 = KSP */
+	br	$17,1f
+
+	ldq	$26,0($30)
+	ldq	$1,8($30)
+	ldq	$2,16($30)
+	ldq	$3,24($30)
+	ldq	$4,32($30)
+	ldq	$5,40($30)
+	ldq	$6,48($30)
+	ldq	$7,56($30)
+	ldq	$8,64($30)
+	ldq	$9,72($30)
+	ldq	$10,80($30)
+	ldq	$11,88($30)
+	ldq	$12,96($30)
+	ldq	$13,104($30)
+	ldq	$14,112($30)
+	ldq	$15,120($30)
+	addq	$30,128,$30
+	ret ($26)
+1:	call_pal PAL_swppal
+	.end	switch_to_osf_pal
+
+	.align 3
+	.globl	tbi
+	.ent	tbi
+tbi:
+	.prologue 0
+	call_pal PAL_tbi
+	ret	($26)
+	.end tbi
+
+	.align 3
+	.globl	halt
+	.ent	halt
+halt:
+	.prologue 0
+	call_pal PAL_halt
+	.end halt
+
+/* $16 - new stack page */
+	.align 3
+	.globl	move_stack
+	.ent	move_stack
+move_stack:
+	.prologue 0
+	lda	$0, 0x1fff($31)
+	and	$0, $30, $1			/* Stack offset */
+	or	$1, $16, $16			/* New stack pointer */
+	mov	$30, $1
+	mov	$16, $2
+1:	ldq	$3, 0($1)			/* Move the stack */
+	addq	$1, 8, $1
+	stq	$3, 0($2)
+	and	$0, $1, $4
+	addq	$2, 8, $2
+	bne	$4, 1b
+	mov	$16, $30
+	ret	($26)
+	.end move_stack