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, 180 insertions, 0 deletions

diff --git a/lib/sg_pool.c b/lib/sg_pool.c
new file mode 100644
index 000000000..9bfe60ca3
--- /dev/null
+++ b/lib/sg_pool.c
@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/init.h>
+#include <linux/scatterlist.h>
+#include <linux/mempool.h>
+#include <linux/slab.h>
+
+#define SG_MEMPOOL_NR		ARRAY_SIZE(sg_pools)
+#define SG_MEMPOOL_SIZE		2
+
+struct sg_pool {
+	size_t		size;
+	char		*name;
+	struct kmem_cache	*slab;
+	mempool_t	*pool;
+};
+
+#define SP(x) { .size = x, "sgpool-" __stringify(x) }
+#if (SG_CHUNK_SIZE < 32)
+#error SG_CHUNK_SIZE is too small (must be 32 or greater)
+#endif
+static struct sg_pool sg_pools[] = {
+	SP(8),
+	SP(16),
+#if (SG_CHUNK_SIZE > 32)
+	SP(32),
+#if (SG_CHUNK_SIZE > 64)
+	SP(64),
+#if (SG_CHUNK_SIZE > 128)
+	SP(128),
+#if (SG_CHUNK_SIZE > 256)
+#error SG_CHUNK_SIZE is too large (256 MAX)
+#endif
+#endif
+#endif
+#endif
+	SP(SG_CHUNK_SIZE)
+};
+#undef SP
+
+static inline unsigned int sg_pool_index(unsigned short nents)
+{
+	unsigned int index;
+
+	BUG_ON(nents > SG_CHUNK_SIZE);
+
+	if (nents <= 8)
+		index = 0;
+	else
+		index = get_count_order(nents) - 3;
+
+	return index;
+}
+
+static void sg_pool_free(struct scatterlist *sgl, unsigned int nents)
+{
+	struct sg_pool *sgp;
+
+	sgp = sg_pools + sg_pool_index(nents);
+	mempool_free(sgl, sgp->pool);
+}
+
+static struct scatterlist *sg_pool_alloc(unsigned int nents, gfp_t gfp_mask)
+{
+	struct sg_pool *sgp;
+
+	sgp = sg_pools + sg_pool_index(nents);
+	return mempool_alloc(sgp->pool, gfp_mask);
+}
+
+/**
+ * sg_free_table_chained - Free a previously mapped sg table
+ * @table:	The sg table header to use
+ * @nents_first_chunk: size of the first_chunk SGL passed to
+ *		sg_alloc_table_chained
+ *
+ *  Description:
+ *    Free an sg table previously allocated and setup with
+ *    sg_alloc_table_chained().
+ *
+ *    @nents_first_chunk has to be same with that same parameter passed
+ *    to sg_alloc_table_chained().
+ *
+ **/
+void sg_free_table_chained(struct sg_table *table,
+		unsigned nents_first_chunk)
+{
+	if (table->orig_nents <= nents_first_chunk)
+		return;
+
+	if (nents_first_chunk == 1)
+		nents_first_chunk = 0;
+
+	__sg_free_table(table, SG_CHUNK_SIZE, nents_first_chunk, sg_pool_free,
+			table->orig_nents);
+}
+EXPORT_SYMBOL_GPL(sg_free_table_chained);
+
+/**
+ * sg_alloc_table_chained - Allocate and chain SGLs in an sg table
+ * @table:	The sg table header to use
+ * @nents:	Number of entries in sg list
+ * @first_chunk: first SGL
+ * @nents_first_chunk: number of the SGL of @first_chunk
+ *
+ *  Description:
+ *    Allocate and chain SGLs in an sg table. If @nents@ is larger than
+ *    @nents_first_chunk a chained sg table will be setup. @first_chunk is
+ *    ignored if nents_first_chunk <= 1 because user expects the SGL points
+ *    non-chain SGL.
+ *
+ **/
+int sg_alloc_table_chained(struct sg_table *table, int nents,
+		struct scatterlist *first_chunk, unsigned nents_first_chunk)
+{
+	int ret;
+
+	BUG_ON(!nents);
+
+	if (first_chunk && nents_first_chunk) {
+		if (nents <= nents_first_chunk) {
+			table->nents = table->orig_nents = nents;
+			sg_init_table(table->sgl, nents);
+			return 0;
+		}
+	}
+
+	/* User supposes that the 1st SGL includes real entry */
+	if (nents_first_chunk <= 1) {
+		first_chunk = NULL;
+		nents_first_chunk = 0;
+	}
+
+	ret = __sg_alloc_table(table, nents, SG_CHUNK_SIZE,
+			       first_chunk, nents_first_chunk,
+			       GFP_ATOMIC, sg_pool_alloc);
+	if (unlikely(ret))
+		sg_free_table_chained(table, nents_first_chunk);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(sg_alloc_table_chained);
+
+static __init int sg_pool_init(void)
+{
+	int i;
+
+	for (i = 0; i < SG_MEMPOOL_NR; i++) {
+		struct sg_pool *sgp = sg_pools + i;
+		int size = sgp->size * sizeof(struct scatterlist);
+
+		sgp->slab = kmem_cache_create(sgp->name, size, 0,
+				SLAB_HWCACHE_ALIGN, NULL);
+		if (!sgp->slab) {
+			printk(KERN_ERR "SG_POOL: can't init sg slab %s\n",
+					sgp->name);
+			goto cleanup_sdb;
+		}
+
+		sgp->pool = mempool_create_slab_pool(SG_MEMPOOL_SIZE,
+						     sgp->slab);
+		if (!sgp->pool) {
+			printk(KERN_ERR "SG_POOL: can't init sg mempool %s\n",
+					sgp->name);
+			goto cleanup_sdb;
+		}
+	}
+
+	return 0;
+
+cleanup_sdb:
+	for (i = 0; i < SG_MEMPOOL_NR; i++) {
+		struct sg_pool *sgp = sg_pools + i;
+
+		mempool_destroy(sgp->pool);
+		kmem_cache_destroy(sgp->slab);
+	}
+
+	return -ENOMEM;
+}
+
+subsys_initcall(sg_pool_init);