linux-kernel - [PATCH 2/5] seqlock: change thread_group_cputime() to use SEQLOCK_READ

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Message-ID: <20251005145023.GA1257@redhat.com>
Date: Sun, 5 Oct 2025 16:50:23 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Alexander Viro <viro@...iv.linux.org.uk>,
	Boqun Feng <boqun.feng@...il.com>,
	David Howells <dhowells@...hat.com>, Ingo Molnar <mingo@...hat.com>,
	Li RongQing <lirongqing@...du.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] seqlock: change thread_group_cputime() to use
 SEQLOCK_READ_SECTION()

To simplify the code and make it more readable.

While at it, change thread_group_cputime() to use __for_each_thread(sig).

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/sched/cputime.c | 14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 7097de2c8cda..2d691075b6d6 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -315,7 +315,6 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
 	struct signal_struct *sig = tsk->signal;
 	u64 utime, stime;
 	struct task_struct *t;
-	unsigned int seq, nextseq;
 	unsigned long flags;
 
 	/*
@@ -330,25 +329,18 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times)
 		(void) task_sched_runtime(current);
 
 	rcu_read_lock();
-	/* Attempt a lockless read on the first round. */
-	nextseq = 0;
-	do {
-		seq = nextseq;
-		flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
+	SEQLOCK_READ_SECTION(&sig->stats_lock, &flags) {
 		times->utime = sig->utime;
 		times->stime = sig->stime;
 		times->sum_exec_runtime = sig->sum_sched_runtime;
 
-		for_each_thread(tsk, t) {
+		__for_each_thread(sig, t) {
 			task_cputime(t, &utime, &stime);
 			times->utime += utime;
 			times->stime += stime;
 			times->sum_exec_runtime += read_sum_exec_runtime(t);
 		}
-		/* If lockless access failed, take the lock. */
-		nextseq = 1;
-	} while (need_seqretry(&sig->stats_lock, seq));
-	done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
+	}
 	rcu_read_unlock();
 }
 
-- 
2.25.1.362.g51ebf55