Re: [PATCH 7/8] lib: convert process iterator to for_each_process_rcu

[Michal Hocko]

On Fri 04-09-26 16:29:59, Ye Liu wrote:
> From: Ye Liu <liuye@xxxxxxxxxx>
> 
> Replace the manual rcu_read_lock()/rcu_read_unlock() pair combined
> with for_each_process() loop in lib/ with for_each_process_rcu().
> 
> No functional change.
> 
> Signed-off-by: Ye Liu <liuye@xxxxxxxxxx>
> ---
>  lib/is_single_threaded.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
> index 8c98b20bfc41..0682dc87bcdf 100644
> --- a/lib/is_single_threaded.c
> +++ b/lib/is_single_threaded.c
> @@ -26,8 +26,7 @@ bool current_is_single_threaded(void)
>  		return true;
>  
>  	ret = false;
> -	rcu_read_lock();
> -	for_each_process(p) {
> +	for_each_process_rcu(p) {
>  		if (unlikely(p->flags & PF_KTHREAD))
>  			continue;
>  		if (unlikely(p == task->group_leader))
> @@ -48,7 +47,5 @@ bool current_is_single_threaded(void)
>  	}
>  	ret = true;
>  found:
> -	rcu_read_unlock();
> -
>  	return ret;

This can be slightly simplified as below. Anyway
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
--- 
diff --git a/lib/is_single_threaded.c b/lib/is_single_threaded.c
index 8c98b20bfc41..4f7620481066 100644
--- a/lib/is_single_threaded.c
+++ b/lib/is_single_threaded.c
@@ -17,7 +17,6 @@ bool current_is_single_threaded(void)
 	struct task_struct *task = current;
 	struct mm_struct *mm = task->mm;
 	struct task_struct *p, *t;
-	bool ret;
 
 	if (atomic_read(&task->signal->live) != 1)
 		return false;
@@ -25,9 +24,7 @@ bool current_is_single_threaded(void)
 	if (atomic_read(&mm->mm_users) == 1)
 		return true;
 
-	ret = false;
-	rcu_read_lock();
-	for_each_process(p) {
+	for_each_process_rcu(p) {
 		if (unlikely(p->flags & PF_KTHREAD))
 			continue;
 		if (unlikely(p == task->group_leader))
@@ -35,7 +32,7 @@ bool current_is_single_threaded(void)
 
 		for_each_thread(p, t) {
 			if (unlikely(t->mm == mm))
-				goto found;
+				return false
 			if (likely(t->mm))
 				break;
 			/*
@@ -46,9 +43,5 @@ bool current_is_single_threaded(void)
 			smp_rmb();
 		}
 	}
-	ret = true;
-found:
-	rcu_read_unlock();
-
-	return ret;
+	return true;
 }
-- 
Michal Hocko
SUSE Labs