[PATCH 5/8] kernel: convert process/thread iterators to for_each_*_rcu

COLD41d

From: Ye Liu <hidden>
Date: 2026-09-04 08:30:55
Also in: linux-pm, lkml, rcu
Subsystem: cpu hotplug, freezer, function hooks (ftrace), hung task detector, locking primitives, read-copy update (rcu), scheduler, the rest, tracing, userspace stack unwinding · Maintainers: Thomas Gleixner, Peter Zijlstra, "Rafael J. Wysocki", Steven Rostedt, Masami Hiramatsu, Andrew Morton, Lance Yang, Ingo Molnar, Will Deacon, Boqun Feng, "Paul E. McKenney", Frederic Weisbecker, Neeraj Upadhyay, Joel Fernandes, Josh Triplett, Uladzislau Rezki, Juri Lelli, Vincent Guittot, Linus Torvalds, Josh Poimboeuf

From: Ye Liu <liuye@kylinos.cn>

Replace the manual rcu_read_lock()/rcu_read_unlock() and guard(rcu)
pairs combined with for_each_process(), for_each_thread() and
for_each_process_thread() loops across kernel/ with the
for_each_*_rcu() macros.

No functional change.

Signed-off-by: Ye Liu <liuye@kylinos.cn>
---
 kernel/cpu.c             | 4 +---
 kernel/freezer.c         | 4 +---
 kernel/hung_task.c       | 7 ++-----
 kernel/locking/lockdep.c | 4 +---
 kernel/rcu/update.c      | 4 +---
 kernel/sched/core.c      | 3 +--
 kernel/sched/debug.c     | 4 +---
 kernel/trace/fgraph.c    | 8 ++------
 kernel/unwind/deferred.c | 3 +--
 9 files changed, 11 insertions(+), 30 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b3c8553d7bd6..bc70fd21561a 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c

@@ -1254,8 +1254,7 @@ void clear_tasks_mm_cpumask(int cpu)
 	 * full-fledged tasklist_lock.
 	 */
 	WARN_ON(cpu_online(cpu));
-	rcu_read_lock();
-	for_each_process(p) {
+	for_each_process_rcu(p) {
 		struct task_struct *t;
 
 		/*

@@ -1268,7 +1267,6 @@ void clear_tasks_mm_cpumask(int cpu)
 		arch_clear_mm_cpumask_cpu(cpu, t->mm);
 		task_unlock(t);
 	}
-	rcu_read_unlock();
 }
 
 /* Take this CPU down. */

diff --git a/kernel/freezer.c b/kernel/freezer.c
index a76bf957fb32..a27b2382fda9 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c

@@ -217,11 +217,9 @@ void thaw_process(struct task_struct *p)
 {
 	struct task_struct *t;
 
-	rcu_read_lock();
-	for_each_thread(p, t) {
+	for_each_thread_rcu(p, t) {
 		__thaw_task(t);
 	}
-	rcu_read_unlock();
 }
 
 /**

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 6fcc94ce4ca9..76871f78497f 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c

@@ -315,8 +315,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 		return;
 
 	this_round_count = 0;
-	rcu_read_lock();
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rcu(g, t) {
 		if (!max_count--)
 			goto unlock;
 		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {

@@ -337,9 +336,7 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
 			hung_task_info(t, timeout, this_round_count);
 		}
 	}
- unlock:
-	rcu_read_unlock();
-
+unlock:
 	if (!this_round_count)
 		return;

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c56a7f91d72e..9c3dce0f0c4b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c

@@ -6834,15 +6834,13 @@ void debug_show_all_locks(void)
 	}
 	pr_warn("\nShowing all locks held in the system:\n");
 
-	rcu_read_lock();
-	for_each_process_thread(g, p) {
+	for_each_process_thread_rcu(g, p) {
 		if (!p->lockdep_depth)
 			continue;
 		lockdep_print_held_locks(p);
 		touch_nmi_watchdog();
 		touch_all_softlockup_watchdogs();
 	}
-	rcu_read_unlock();
 
 	pr_warn("\n");
 	pr_warn("=============================================\n\n");

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 2a778b8ab4ad..c48a84a0da82 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c

@@ -548,15 +548,13 @@ void synchronize_rcu_trivial_preempt(void)
 	struct task_struct *t;
 
 	smp_mb(); // Order prior accesses before grace-period start.
-	rcu_read_lock(); // Protect task list.
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rcu(g, t) {
 		if (t == current)
 			continue;  // Don't deadlock on ourselves!
 		// Order later rcu_read_lock() on other tasks after QS.
 		while (smp_load_acquire(&t->rcu_trivial_preempt_nesting))
 			continue;
 	}
-	rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu_trivial_preempt);
 #endif // #if IS_ENABLED(CONFIG_TRIVIAL_PREEMPT_RCU)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0697ed0f1c3d..a41cdd2ff02f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c

@@ -2005,8 +2005,7 @@ static void uclamp_sync_util_min_rt_default(void)
 	smp_mb__after_spinlock();
 	read_unlock(&tasklist_lock);
 
-	guard(rcu)();
-	for_each_process_thread(g, p)
+	for_each_process_thread_rcu(g, p)
 		uclamp_update_util_min_rt_default(p);
 }

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 72236db67983..8f37b1a7adfe 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c

@@ -1029,14 +1029,12 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
 #endif
 		   "\n");
 
-	rcu_read_lock();
-	for_each_process_thread(g, p) {
+	for_each_process_thread_rcu(g, p) {
 		if (task_cpu(p) != rq_cpu)
 			continue;
 
 		print_task(m, rq, p);
 	}
-	rcu_read_unlock();
 }
 
 void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 40d373d65f9b..e522433ec8a5 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c

@@ -1057,11 +1057,10 @@ static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
 		}
 	}
 
-	rcu_read_lock();
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rcu(g, t) {
 		if (start == end) {
 			ret = -EAGAIN;
-			goto unlock;
+			goto free;
 		}
 
 		if (t->ret_stack == NULL) {

@@ -1074,9 +1073,6 @@ static int alloc_retstack_tasklist(unsigned long **ret_stack_list)
 			t->ret_stack = ret_stack_list[start++];
 		}
 	}
-
-unlock:
-	rcu_read_unlock();
 free:
 	for (i = start; i < end; i++)
 		kmem_cache_free(fgraph_stack_cachep, ret_stack_list[i]);

diff --git a/kernel/unwind/deferred.c b/kernel/unwind/deferred.c
index 5bea47314254..61fe2d4727ce 100644
--- a/kernel/unwind/deferred.c
+++ b/kernel/unwind/deferred.c

@@ -319,9 +319,8 @@ void unwind_deferred_cancel(struct unwind_work *work)
 
 	synchronize_srcu(&unwind_srcu);
 
-	guard(rcu)();
 	/* Clear this bit from all threads */
-	for_each_process_thread(g, t) {
+	for_each_process_thread_rcu(g, t) {
 		atomic_long_andnot(BIT(bit),
 				   &t->unwind_info.unwind_mask);
 		if (t->unwind_info.cache)

-- 
2.25.1

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