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, 30 insertions, 0 deletions

diff --git a/tools/lib/perf/TODO b/tools/lib/perf/TODO
new file mode 100644
index 000000000..e17972869
--- /dev/null
+++ b/tools/lib/perf/TODO
@@ -0,0 +1,30 @@
+Future ABI changes
+==================
+
+This file collects items that require a libperf ABI bump.  Each entry
+should describe the current limitation, the desired end state, and the
+scope of the change so that a future ABI revision can batch them
+together.
+
+1. Widen struct perf_cpu.cpu from int16_t to int
+   - Current limit: 32767 CPUs.  No architecture exceeds this today
+     (x86_64 max is 8192, arm64 is 4096), but NR_CPUS limits keep
+     growing.  perf clamps to INT16_MAX in set_max_cpu_num() as a
+     safety net.
+   - Code simplification: the int16_t forces defensive truncation
+     checks at every boundary where a wider CPU index (int from
+     sample->cpu, al->cpu, etc.) is narrowed into struct perf_cpu.
+     Without these checks, values > 32767 silently wrap to negative
+     numbers (two's complement), bypassing bounds validation.
+     Widening to int eliminates this entire class of silent
+     truncation bugs and removes the need for the INT16_MAX clamp
+     in set_max_cpu_num().
+   - Scope: struct perf_cpu is embedded everywhere — perf_cpu_map__cpu(),
+     perf_cpu_map__min(), perf_cpu_map__max(), perf_cpu_map__has(), the
+     for_each_cpu macros, and all internal callers.  The perf_cpu_map
+     internal array (RC_CHK_ACCESS(map)->map[]) stores struct perf_cpu
+     directly.  Widening changes the struct layout and every function
+     that returns or accepts struct perf_cpu by value.
+   - Migration: bump LIBPERF version in libperf.map, audit all
+     sizeof(struct perf_cpu) assumptions, update perf.data
+     serialization if needed.