From: Phil Auld <pauld@redhat.com>
To: linux-kernel <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Waiman Long <longman@redhat.com>, Ingo Molnar <mingo@kernel.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
stable@vger.kernel.org, Phil Auld <pauld@redhat.com>
Subject: [PATCH] sched: Fix nr_uninterruptible race causing increasing load average
Date: Wed, 7 Jul 2021 15:04:57 -0400 [thread overview]
Message-ID: <20210707190457.60521-1-pauld@redhat.com> (raw)
On systems with weaker memory ordering (e.g. power) commit dbfb089d360b
("sched: Fix loadavg accounting race") causes increasing values of load
average (via rq->calc_load_active and calc_load_tasks) due to the wakeup
CPU not always seeing the write to task->sched_contributes_to_load in
__schedule(). Missing that we fail to decrement nr_uninterruptible when
waking up a task which incremented nr_uninterruptible when it slept.
The rq->lock serialization is insufficient across different rq->locks.
Add smp_wmb() to schedule and smp_rmb() before the read in
ttwu_do_activate().
Fixes: dbfb089d360b ("sched: Fix loadavg accounting race")
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Waiman Long <longman@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Phil Auld <pauld@redhat.com>
---
kernel/sched/core.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4ca80df205ce..ced7074716eb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2992,6 +2992,8 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
lockdep_assert_held(&rq->lock);
+ /* Pairs with smp_wmb in __schedule() */
+ smp_rmb();
if (p->sched_contributes_to_load)
rq->nr_uninterruptible--;
@@ -5084,6 +5086,11 @@ static void __sched notrace __schedule(bool preempt)
!(prev_state & TASK_NOLOAD) &&
!(prev->flags & PF_FROZEN);
+ /*
+ * Make sure the previous write is ordered before p->on_rq etc so
+ * that it is visible to other cpus in the wakeup path (ttwu_do_activate()).
+ */
+ smp_wmb();
if (prev->sched_contributes_to_load)
rq->nr_uninterruptible++;
--
2.18.0
next reply other threads:[~2021-07-07 19:05 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-07 19:04 Phil Auld [this message]
2021-07-08 7:26 ` [PATCH] sched: Fix nr_uninterruptible race causing increasing load average Peter Zijlstra
2021-07-08 7:48 ` Peter Zijlstra
2021-07-08 7:54 ` Peter Zijlstra
2021-07-08 14:54 ` Phil Auld
2021-07-09 12:57 ` Peter Zijlstra
2021-07-11 13:19 ` Phil Auld
2021-07-08 13:25 ` Phil Auld
2021-07-09 11:38 ` Peter Zijlstra
2021-07-11 12:57 ` Phil Auld
2021-07-23 13:38 ` Phil Auld
2021-07-28 15:45 ` Phil Auld
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=20210707190457.60521-1-pauld@redhat.com \
--to=pauld@redhat.com \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=longman@redhat.com \
--cc=mingo@kernel.org \
--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;
as well as URLs for NNTP newsgroup(s).