From: John Stultz <jstultz@google.com>
To: stable@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>,
John Stultz <jstultz@google.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
K Prateek Nayak <kprateek.nayak@amd.com>
Subject: [PATCH 6.18] sched/debug: Fix avg_vruntime() usage
Date: Thu, 23 Apr 2026 01:26:16 +0000 [thread overview]
Message-ID: <20260423012619.980559-1-jstultz@google.com> (raw)
From: Peter Zijlstra <peterz@infradead.org>
commit e08d007f9d813616ce7093600bc4fdb9c9d81d89 upstream.
John reported that stress-ng-yield could make his machine unhappy and
managed to bisect it to commit b3d99f43c72b ("sched/fair: Fix
zero_vruntime tracking").
The commit in question changes avg_vruntime() from a function that is
a pure reader, to a function that updates variables. This turns an
unlocked sched/debug usage of this function from a minor mistake into
a data corruptor.
Fixes: af4cf40470c2 ("sched/fair: Add cfs_rq::avg_vruntime")
Fixes: b3d99f43c72b ("sched/fair: Fix zero_vruntime tracking")
Reported-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20260401132355.196370805@infradead.org
Signed-off-by: John Stultz <jstultz@google.com>
---
kernel/sched/debug.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 93f009e1076d8..3504ec9bd7307 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -798,6 +798,7 @@ static void print_rq(struct seq_file *m, struct rq *rq, int rq_cpu)
void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
{
s64 left_vruntime = -1, zero_vruntime, right_vruntime = -1, left_deadline = -1, spread;
+ u64 avruntime;
struct sched_entity *last, *first, *root;
struct rq *rq = cpu_rq(cpu);
unsigned long flags;
@@ -821,6 +822,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
if (last)
right_vruntime = last->vruntime;
zero_vruntime = cfs_rq->zero_vruntime;
+ avruntime = avg_vruntime(cfs_rq);
raw_spin_rq_unlock_irqrestore(rq, flags);
SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "left_deadline",
@@ -830,7 +832,7 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq)
SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "zero_vruntime",
SPLIT_NS(zero_vruntime));
SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "avg_vruntime",
- SPLIT_NS(avg_vruntime(cfs_rq)));
+ SPLIT_NS(avruntime));
SEQ_printf(m, " .%-30s: %Ld.%06ld\n", "right_vruntime",
SPLIT_NS(right_vruntime));
spread = right_vruntime - left_vruntime;
--
2.54.0.rc2.533.g4f5dca5207-goog
reply other threads:[~2026-04-23 1:26 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260423012619.980559-1-jstultz@google.com \
--to=jstultz@google.com \
--cc=kprateek.nayak@amd.com \
--cc=peterz@infradead.org \
--cc=stable@vger.kernel.org \
--cc=vincent.guittot@linaro.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox