linux-kernel - [PATCH 1/3] fs/proc: do_task_stat: move thread_group_cputime_adjusted() outside of lock_task

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Date: Tue, 23 Jan 2024 16:33:55 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
	Dylan Hatch <dylanbhatch@...gle.com>, linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] fs/proc: do_task_stat: move
 thread_group_cputime_adjusted() outside of lock_task_sighand()

thread_group_cputime() does its own locking, we can safely shift
thread_group_cputime_adjusted() which does another for_each_thread loop
outside of ->siglock protected section.

Not only this removes for_each_thread() from the critical section with
irqs disabled, this removes another case when stats_lock is taken with
siglock held. We want to remove this dependency, then we can change the
users of stats_lock to not disable irqs.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/proc/array.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index ff08a8957552..45ba91863808 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -511,7 +511,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 
 	sigemptyset(&sigign);
 	sigemptyset(&sigcatch);
-	cutime = cstime = utime = stime = 0;
+	cutime = cstime = 0;
 	cgtime = gtime = 0;
 
 	if (lock_task_sighand(task, &flags)) {
@@ -546,7 +546,6 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 
 			min_flt += sig->min_flt;
 			maj_flt += sig->maj_flt;
-			thread_group_cputime_adjusted(task, &utime, &stime);
 			gtime += sig->gtime;
 
 			if (sig->flags & (SIGNAL_GROUP_EXIT | SIGNAL_STOP_STOPPED))
@@ -562,10 +561,13 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 
 	if (permitted && (!whole || num_threads < 2))
 		wchan = !task_is_running(task);
-	if (!whole) {
+
+	if (whole) {
+		thread_group_cputime_adjusted(task, &utime, &stime);
+	} else {
+		task_cputime_adjusted(task, &utime, &stime);
 		min_flt = task->min_flt;
 		maj_flt = task->maj_flt;
-		task_cputime_adjusted(task, &utime, &stime);
 		gtime = task_gtime(task);
 	}
 
-- 
2.25.1.362.g51ebf55