[PATCH v2 5/8] kernel: convert process/thread iterators to for_each_*_rculock

[Ye Liu]

From: Ye Liu <liuye at 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_*_rculock() macros, which scope the RCU read lock to the
loop body via scoped_guard(rcu).

No functional change.

Signed-off-by: Ye Liu <liuye at kylinos.cn>
Acked-by: Michal Hocko <mhocko at suse.com>
---
Changes in v2:
  - Rename *_rcu to *_rculock
  - Rename stale 'unlock:' label to 'out:' in hung_task.c (Günther Noack)
 kernel/cpu.c             |  4 +---
 kernel/freezer.c         |  4 +---
 kernel/hung_task.c       | 11 ++++-------
 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, 13 insertions(+), 32 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b3c8553d7bd6..00638d2abc0f 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_rculock(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..7a870f71dcf6 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_rculock(p, t) {
 		__thaw_task(t);
 	}
-	rcu_read_unlock();
 }
 
 /**
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 6fcc94ce4ca9..73a5ad3be9a8 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -315,13 +315,12 @@ 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_rculock(g, t) {
 		if (!max_count--)
-			goto unlock;
+			goto out;
 		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
 			if (!rcu_lock_break(g, t))
-				goto unlock;
+				goto out;
 			last_break = jiffies;
 		}
 
@@ -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();
-
+out:
 	if (!this_round_count)
 		return;
 
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index c56a7f91d72e..ea218dc75ad5 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_rculock(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..d8e0b5896db9 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_rculock(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..fd5bdd2cb798 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_rculock(g, p)
 		uclamp_update_util_min_rt_default(p);
 }
 
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 72236db67983..cdae165b98f7 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_rculock(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..f797ce119223 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_rculock(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..ecfe1336095e 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_rculock(g, t) {
 		atomic_long_andnot(BIT(bit),
 				   &t->unwind_info.unwind_mask);
 		if (t->unwind_info.cache)
-- 
2.25.1