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, 166 insertions, 0 deletions

diff --git a/fs/btrfs/lru_cache.c b/fs/btrfs/lru_cache.c
new file mode 100644
index 000000000..f5a053b90
--- /dev/null
+++ b/fs/btrfs/lru_cache.c
@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/mm.h>
+#include "lru_cache.h"
+#include "messages.h"
+
+/*
+ * Initialize a cache object.
+ *
+ * @cache:      The cache.
+ * @max_size:   Maximum size (number of entries) for the cache.
+ *              Use 0 for unlimited size, it's the user's responsibility to
+ *              trim the cache in that case.
+ */
+void btrfs_lru_cache_init(struct btrfs_lru_cache *cache, unsigned int max_size)
+{
+	INIT_LIST_HEAD(&cache->lru_list);
+	mt_init(&cache->entries);
+	cache->size = 0;
+	cache->max_size = max_size;
+}
+
+static struct btrfs_lru_cache_entry *match_entry(struct list_head *head, u64 key,
+						 u64 gen)
+{
+	struct btrfs_lru_cache_entry *entry;
+
+	list_for_each_entry(entry, head, list) {
+		if (entry->key == key && entry->gen == gen)
+			return entry;
+	}
+
+	return NULL;
+}
+
+/*
+ * Lookup for an entry in the cache.
+ *
+ * @cache:      The cache.
+ * @key:        The key of the entry we are looking for.
+ * @gen:        Generation associated to the key.
+ *
+ * Returns the entry associated with the key or NULL if none found.
+ */
+struct btrfs_lru_cache_entry *btrfs_lru_cache_lookup(struct btrfs_lru_cache *cache,
+						     u64 key, u64 gen)
+{
+	struct list_head *head;
+	struct btrfs_lru_cache_entry *entry;
+
+	head = mtree_load(&cache->entries, key);
+	if (!head)
+		return NULL;
+
+	entry = match_entry(head, key, gen);
+	if (entry)
+		list_move_tail(&entry->lru_list, &cache->lru_list);
+
+	return entry;
+}
+
+/*
+ * Remove an entry from the cache.
+ *
+ * @cache:     The cache to remove from.
+ * @entry:     The entry to remove from the cache.
+ *
+ * Note: this also frees the memory used by the entry.
+ */
+void btrfs_lru_cache_remove(struct btrfs_lru_cache *cache,
+			    struct btrfs_lru_cache_entry *entry)
+{
+	struct list_head *prev = entry->list.prev;
+
+	ASSERT(cache->size > 0);
+	ASSERT(!mtree_empty(&cache->entries));
+
+	list_del(&entry->list);
+	list_del(&entry->lru_list);
+
+	if (list_empty(prev)) {
+		struct list_head *head;
+
+		/*
+		 * If previous element in the list entry->list is now empty, it
+		 * means it's a head entry not pointing to any cached entries,
+		 * so remove it from the maple tree and free it.
+		 */
+		head = mtree_erase(&cache->entries, entry->key);
+		ASSERT(head == prev);
+		kfree(head);
+	}
+
+	kfree(entry);
+	cache->size--;
+}
+
+/*
+ * Store an entry in the cache.
+ *
+ * @cache:      The cache.
+ * @entry:      The entry to store.
+ *
+ * Returns 0 on success and < 0 on error.
+ */
+int btrfs_lru_cache_store(struct btrfs_lru_cache *cache,
+			  struct btrfs_lru_cache_entry *new_entry,
+			  gfp_t gfp)
+{
+	const u64 key = new_entry->key;
+	struct list_head *head;
+	int ret;
+
+	head = kmalloc_obj(*head, gfp);
+	if (!head)
+		return -ENOMEM;
+
+	ret = mtree_insert(&cache->entries, key, head, gfp);
+	if (ret == 0) {
+		INIT_LIST_HEAD(head);
+		list_add_tail(&new_entry->list, head);
+	} else if (ret == -EEXIST) {
+		kfree(head);
+		head = mtree_load(&cache->entries, key);
+		ASSERT(head != NULL);
+		if (match_entry(head, key, new_entry->gen) != NULL)
+			return -EEXIST;
+		list_add_tail(&new_entry->list, head);
+	} else if (ret < 0) {
+		kfree(head);
+		return ret;
+	}
+
+	if (cache->max_size > 0 && cache->size == cache->max_size) {
+		struct btrfs_lru_cache_entry *lru_entry;
+
+		lru_entry = list_first_entry(&cache->lru_list,
+					     struct btrfs_lru_cache_entry,
+					     lru_list);
+		btrfs_lru_cache_remove(cache, lru_entry);
+	}
+
+	list_add_tail(&new_entry->lru_list, &cache->lru_list);
+	cache->size++;
+
+	return 0;
+}
+
+/*
+ * Empty a cache.
+ *
+ * @cache:     The cache to empty.
+ *
+ * Removes all entries from the cache.
+ */
+void btrfs_lru_cache_clear(struct btrfs_lru_cache *cache)
+{
+	struct btrfs_lru_cache_entry *entry;
+	struct btrfs_lru_cache_entry *tmp;
+
+	list_for_each_entry_safe(entry, tmp, &cache->lru_list, lru_list)
+		btrfs_lru_cache_remove(cache, entry);
+
+	ASSERT(cache->size == 0);
+	ASSERT(mtree_empty(&cache->entries));
+}