From: Peter Zijlstra <peterz@infradead.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: mingo@kernel.org, tglx@linutronix.de,
linux-kernel@vger.kernel.org, jiangshanlai@gmail.com,
cai@redhat.com, vincent.donnefort@arm.com, decui@microsoft.com,
paulmck@kernel.org, vincent.guittot@linaro.org,
rostedt@goodmis.org, tj@kernel.org
Subject: Re: [PATCH -v3 8/9] sched: Fix CPU hotplug / tighten is_per_cpu_kthread()
Date: Thu, 21 Jan 2021 15:18:10 +0100 [thread overview]
Message-ID: <YAmNIsyaiO6teljH@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <jhjeeiemlsw.mognet@arm.com>
On Thu, Jan 21, 2021 at 02:01:03PM +0000, Valentin Schneider wrote:
> On 21/01/21 11:17, Peter Zijlstra wrote:
> > @@ -7504,6 +7525,9 @@ int sched_cpu_deactivate(unsigned int cp
> > * preempt-disabled and RCU users of this state to go away such that
> > * all new such users will observe it.
> > *
> > + * Specifically, we rely on ttwu to no longer target this CPU, see
> > + * ttwu_queue_cond() and is_cpu_allowed().
> > + *
>
> So the last time ttwu_queue_wakelist() can append a task onto a dying
> CPU's wakelist is before sched_cpu_deactivate()'s synchronize_rcu()
> returns.
>
> As discussed on IRC, paranoia would have us issue a
>
> flush_smp_call_function_from_idle()
>
> upon returning from said sync, but this will require further surgery.
Right, specifically RCU needs a little more help there.
> Do we want something like the below in the meantime? Ideally we'd warn on
> setting rq->ttwu_pending when !cpu_active(), but as per the above this is
> allowed before the synchronize_rcu() returns.
I'm not sure I'm brave enough to add that just now :/
next prev parent reply other threads:[~2021-01-21 14:25 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 10:17 [PATCH -v3 0/9] sched: Fix hot-unplug regression Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 1/9] sched/core: Print out straggler tasks in sched_cpu_dying() Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 2/9] workqueue: Use cpu_possible_mask instead of cpu_active_mask to break affinity Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 3/9] sched: Dont run cpu-online with balance_push() enabled Peter Zijlstra
2021-01-21 14:00 ` Valentin Schneider
2021-01-21 14:14 ` Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] sched: Don't " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 4/9] kthread: Extract KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 5/9] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU Peter Zijlstra
2021-01-21 14:31 ` Valentin Schneider
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 6/9] workqueue: Restrict affinity change to rescuer Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 7/9] sched: Prepare to use balance_push in ttwu() Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 8/9] sched: Fix CPU hotplug / tighten is_per_cpu_kthread() Peter Zijlstra
2021-01-21 14:01 ` Valentin Schneider
2021-01-21 14:18 ` Peter Zijlstra [this message]
2021-01-21 14:36 ` Valentin Schneider
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 10:17 ` [PATCH -v3 9/9] sched: Relax the set_cpus_allowed_ptr() semantics Peter Zijlstra
2021-01-22 17:41 ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-01-21 14:36 ` [PATCH -v3 0/9] sched: Fix hot-unplug regression Valentin Schneider
2021-01-21 19:56 ` Paul E. McKenney
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