From: Frederic Weisbecker <frederic@kernel.org>
To: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Jacek Anaszewski <jacek.anaszewski@gmail.com>,
Wanpeng Li <wanpengli@tencent.com>,
"Rafael J . Wysocki" <rjw@rjwysocki.net>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Rik van Riel <riel@surriel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Yauheni Kaliuta <yauheni.kaliuta@redhat.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH 2/6] sched/vtime: Bring up complete kcpustat accessor
Date: Mon, 30 Dec 2019 02:08:40 +0100 [thread overview]
Message-ID: <20191230010839.GA8740@lenoir> (raw)
In-Reply-To: <157756657962.14652.10349541055640858962@skylake-alporthouse-com>
On Sat, Dec 28, 2019 at 08:56:19PM +0000, Chris Wilson wrote:
> I'm randomly hitting this WARN on a non-virtualised system reading
> /proc/stat.
>
> vtime->state is updated under the write_seqcount, so the access here is
> deliberately racey, and the change in vtime->state would be picked up
> the seqcount_retry.
>
> Quick suggestion would be something along the lines of
>
> static int vtime_state_check(struct vtime *vtime, int cpu)
> {
> + int state = READ_ONCE(vtime->state);
> +
> /*
> * We raced against a context switch, fetch the
> * kcpustat task again.
> @@ -930,10 +932,10 @@ static int vtime_state_check(struct vtime *vtime, int cpu)
> *
> * Case 1) is ok but 2) is not. So wait for a safe VTIME state.
> */
> - if (vtime->state == VTIME_INACTIVE)
> + if (state == VTIME_INACTIVE)
> return -EAGAIN;
>
> - return 0;
> + return state;
> }
>
> static u64 kcpustat_user_vtime(struct vtime *vtime)
> @@ -1055,7 +1057,7 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst,
> cpustat = dst->cpustat;
>
> /* Task is sleeping, dead or idle, nothing to add */
> - if (vtime->state < VTIME_SYS)
> + if (err < VTIME_SYS)
> continue;
>
> delta = vtime_delta(vtime);
> @@ -1064,15 +1066,15 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst,
> * Task runs either in user (including guest) or kernel space,
> * add pending nohz time to the right place.
> */
> - if (vtime->state == VTIME_SYS) {
> + if (err == VTIME_SYS) {
> cpustat[CPUTIME_SYSTEM] += vtime->stime + delta;
> - } else if (vtime->state == VTIME_USER) {
> + } else if (err == VTIME_USER) {
> if (task_nice(tsk) > 0)
> cpustat[CPUTIME_NICE] += vtime->utime + delta;
> else
> cpustat[CPUTIME_USER] += vtime->utime + delta;
> } else {
> - WARN_ON_ONCE(vtime->state != VTIME_GUEST);
> + WARN_ON_ONCE(err != VTIME_GUEST);
> if (task_nice(tsk) > 0) {
> cpustat[CPUTIME_GUEST_NICE] += vtime->gtime + delta;
> cpustat[CPUTIME_NICE] += vtime->gtime + delta;
>
> Or drop the warn.
Good catch, can I use your Signed-off-by ?
Thanks.
next prev parent reply other threads:[~2019-12-30 1:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-21 2:44 [PATCH 0/6] sched/nohz: Make the rest of kcpustat vtime aware v3 Frederic Weisbecker
2019-11-21 2:44 ` [PATCH 1/6] sched/cputime: Support other fields on kcpustat_field() Frederic Weisbecker
2019-11-21 16:48 ` [tip: sched/core] " tip-bot2 for Frederic Weisbecker
2019-11-21 2:44 ` [PATCH 2/6] sched/vtime: Bring up complete kcpustat accessor Frederic Weisbecker
2019-11-21 16:48 ` [tip: sched/core] " tip-bot2 for Frederic Weisbecker
2019-12-28 20:56 ` [PATCH 2/6] " Chris Wilson
2019-12-30 1:08 ` Frederic Weisbecker [this message]
2019-12-30 9:04 ` [PATCH] sched/vtime: Prevent unstable evaluation of WARN(vtime->state) Chris Wilson
2019-12-30 17:39 ` Frederic Weisbecker
2019-11-21 2:44 ` [PATCH 3/6] procfs: Use all-in-one vtime aware kcpustat accessor Frederic Weisbecker
2019-11-21 16:48 ` [tip: sched/core] " tip-bot2 for Frederic Weisbecker
2019-12-08 15:57 ` [PATCH 3/6] " Paul Orlyk
2019-12-09 15:50 ` Frederic Weisbecker
2019-11-21 2:44 ` [PATCH 4/6] cpufreq: Use vtime aware kcpustat accessors for user time Frederic Weisbecker
2019-11-21 16:48 ` [tip: sched/core] " tip-bot2 for Frederic Weisbecker
2019-11-21 2:44 ` [PATCH 5/6] leds: Use all-in-one vtime aware kcpustat accessor Frederic Weisbecker
2019-11-21 6:58 ` Ingo Molnar
2019-11-21 14:14 ` Frederic Weisbecker
2019-11-21 16:49 ` Ingo Molnar
2019-11-21 16:48 ` [tip: sched/core] " tip-bot2 for Frederic Weisbecker
2019-11-21 2:44 ` [PATCH 6/6] rackmeter: Use " Frederic Weisbecker
2019-11-21 16:48 ` [tip: sched/core] " tip-bot2 for Frederic Weisbecker
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