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, 96 insertions, 0 deletions

diff --git a/net/rxrpc/txbuf.c b/net/rxrpc/txbuf.c
new file mode 100644
index 000000000..55ef7a048
--- /dev/null
+++ b/net/rxrpc/txbuf.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* RxRPC Tx data buffering.
+ *
+ * Copyright (C) 2022 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/slab.h>
+#include "ar-internal.h"
+
+static atomic_t rxrpc_txbuf_debug_ids;
+atomic_t rxrpc_nr_txbuf;
+
+/*
+ * Allocate and partially initialise a data transmission buffer.
+ */
+struct rxrpc_txbuf *rxrpc_alloc_data_txbuf(struct rxrpc_call *call, size_t data_size,
+					   size_t data_align, gfp_t gfp)
+{
+	struct rxrpc_txbuf *txb;
+	size_t total, doff, jsize = sizeof(struct rxrpc_jumbo_header);
+	void *buf;
+
+	txb = kzalloc_obj(*txb, gfp);
+	if (!txb)
+		return NULL;
+
+	/* We put a jumbo header in the buffer, but not a full wire header to
+	 * avoid delayed-corruption problems with zerocopy.
+	 */
+	doff = round_up(jsize, data_align);
+	total = doff + data_size;
+
+	data_align = umax(data_align, L1_CACHE_BYTES);
+	mutex_lock(&call->conn->tx_data_alloc_lock);
+	buf = page_frag_alloc_align(&call->conn->tx_data_alloc, total, gfp,
+				    data_align);
+	mutex_unlock(&call->conn->tx_data_alloc_lock);
+	if (!buf) {
+		kfree(txb);
+		return NULL;
+	}
+
+	refcount_set(&txb->ref, 1);
+	txb->call_debug_id	= call->debug_id;
+	txb->debug_id		= atomic_inc_return(&rxrpc_txbuf_debug_ids);
+	txb->alloc_size		= data_size;
+	txb->space		= data_size;
+	txb->offset		= 0;
+	txb->flags		= call->conn->out_clientflag;
+	txb->seq		= call->send_top + 1;
+	txb->data		= buf + doff;
+
+	trace_rxrpc_txbuf(txb->debug_id, txb->call_debug_id, txb->seq, 1,
+			  rxrpc_txbuf_alloc_data);
+
+	atomic_inc(&rxrpc_nr_txbuf);
+	return txb;
+}
+
+void rxrpc_see_txbuf(struct rxrpc_txbuf *txb, enum rxrpc_txbuf_trace what)
+{
+	int r = refcount_read(&txb->ref);
+
+	trace_rxrpc_txbuf(txb->debug_id, txb->call_debug_id, txb->seq, r, what);
+}
+
+static void rxrpc_free_txbuf(struct rxrpc_txbuf *txb)
+{
+	trace_rxrpc_txbuf(txb->debug_id, txb->call_debug_id, txb->seq, 0,
+			  rxrpc_txbuf_free);
+	if (txb->data)
+		page_frag_free(txb->data);
+	kfree(txb);
+	atomic_dec(&rxrpc_nr_txbuf);
+}
+
+void rxrpc_put_txbuf(struct rxrpc_txbuf *txb, enum rxrpc_txbuf_trace what)
+{
+	unsigned int debug_id, call_debug_id;
+	rxrpc_seq_t seq;
+	bool dead;
+	int r;
+
+	if (txb) {
+		debug_id = txb->debug_id;
+		call_debug_id = txb->call_debug_id;
+		seq = txb->seq;
+		dead = __refcount_dec_and_test(&txb->ref, &r);
+		trace_rxrpc_txbuf(debug_id, call_debug_id, seq, r - 1, what);
+		if (dead)
+			rxrpc_free_txbuf(txb);
+	}
+}