From: Lai Jiangshan <jiangshanlai@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Qian Cai <cai@redhat.com>,
Vincent Donnefort <vincent.donnefort@arm.com>,
Dexuan Cui <decui@microsoft.com>,
Lai Jiangshan <laijs@linux.alibaba.com>,
Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH -tip V3 3/8] workqueue: introduce wq_online_cpumask
Date: Tue, 5 Jan 2021 16:23:44 +0800 [thread overview]
Message-ID: <CAJhGHyCwyuzikMZAxub=rxn9oe-N2P5C8CEOmyigd9d55SV5YA@mail.gmail.com> (raw)
In-Reply-To: <CAJhGHyB_MUHG8GGANcN9sQbjY7M5m8WPHQgXp-PmkGK481M5Tg@mail.gmail.com>
On Tue, Jan 5, 2021 at 10:41 AM Lai Jiangshan <jiangshanlai@gmail.com> wrote:
>
> On Mon, Jan 4, 2021 at 9:56 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Sat, Dec 26, 2020 at 10:51:11AM +0800, Lai Jiangshan wrote:
> > > From: Lai Jiangshan <laijs@linux.alibaba.com>
> > >
> > > wq_online_cpumask is the cached result of cpu_online_mask with the
> > > going-down cpu cleared.
> >
> > You can't use cpu_active_mask ?
>
>
> When a cpu is going out:
> (cpu_active_mask is not protected by workqueue mutexs.)
>
> create_worker() for unbound pool | cpu offlining
> check cpu_active_mask |
check wq_online_cpumask
> | remove bit from cpu_active_mask
> | no cpu in pool->attrs->cpumask is active
> set pool->attrs->cpumask to worker|
> and hit the warning
| remove bit from wq_online_cpumask
Even with the help of wq_online_cpumask, the patchset can't silence
the warning in __set_cpus_allowed_ptr() in this case. It is indeed
hard to suppress the warning for unbound pools. Maybe we need something
like this (outmost callback of CPUHP_AP_WORKQUEUE_UNBOUND_ONLINE,
so that workqueue can do preparation when offlining before AP_ACTIVE):
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 0042ef362511..ac2103deb20b 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -20,6 +20,9 @@
* | ^
* v |
* AP_ACTIVE AP_ACTIVE
+ * | ^
+ * v |
+ * ONLINE ONLINE
*/
enum cpuhp_state {
@@ -194,6 +197,7 @@ enum cpuhp_state {
CPUHP_AP_X86_HPET_ONLINE,
CPUHP_AP_X86_KVM_CLK_ONLINE,
CPUHP_AP_ACTIVE,
+ CPUHP_AP_WORKQUEUE_UNBOUND_ONLINE,
CPUHP_ONLINE,
};
The other way is to modify __set_cpus_allowed_ptr() to suppress the
warning for kworkers and believe/let the workqueue handle cpumask correctly.
And the third way is to use get_online_cpus() in worker_attach_to_pool()
which might delay work items to be processed during cpuhotplug and might
be dangerous when someone call flush_work() in cpuhotplug callbacks.
Any thoughts?
Thanks,
Lai
>
>
> And when a cpu is onlining, there may be some workers which were just created
> after the workqueue hotplug callback is finished but before cpu_active_mask
> was updated. workqueue has not call back after cpu_active_mask updated and
> these workers' cpumask is not updated.
>
> For percpu workers, these problems can be handled with the help of
> POOL_DISASSOCIATED which is protected by workqueue mutexs and the
> help of sched/core.c which doesn't warn when per-cpu-kthread.
>
> For unbound workers, the way to handle it without using wq_online_cpumask
> is much more complex when a cpu is going out.
next prev parent reply other threads:[~2021-01-05 8:24 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-26 2:51 [PATCH -tip V3 0/8] workqueue: break affinity initiatively Lai Jiangshan
2020-12-26 2:51 ` [PATCH -tip V3 1/8] workqueue: use cpu_possible_mask instead of cpu_active_mask to break affinity Lai Jiangshan
2020-12-26 2:51 ` [PATCH -tip V3 2/8] workqueue: Manually break affinity on pool detachment Lai Jiangshan
2020-12-26 2:51 ` [PATCH -tip V3 3/8] workqueue: introduce wq_online_cpumask Lai Jiangshan
2021-01-04 13:56 ` Peter Zijlstra
2021-01-05 2:41 ` Lai Jiangshan
2021-01-05 2:53 ` Lai Jiangshan
2021-01-05 8:23 ` Lai Jiangshan [this message]
2021-01-05 13:17 ` Peter Zijlstra
2021-01-05 14:37 ` Lai Jiangshan
2021-01-05 14:40 ` Lai Jiangshan
2021-01-05 16:24 ` Peter Zijlstra
2020-12-26 2:51 ` [PATCH -tip V3 4/8] workqueue: use wq_online_cpumask in restore_unbound_workers_cpumask() Lai Jiangshan
2020-12-26 2:51 ` [PATCH -tip V3 5/8] workqueue: Manually break affinity on hotplug for unbound pool Lai Jiangshan
[not found] ` <20201226101631.5448-1-hdanton@sina.com>
2020-12-27 14:04 ` Lai Jiangshan
2020-12-26 2:51 ` [PATCH -tip V3 6/8] workqueue: reorganize workqueue_online_cpu() Lai Jiangshan
2020-12-26 2:51 ` [PATCH -tip V3 7/8] workqueue: reorganize workqueue_offline_cpu() unbind_workers() Lai Jiangshan
2020-12-26 2:51 ` [PATCH -tip V3 8/8] workqueue: Fix affinity of kworkers when attaching into pool Lai Jiangshan
[not found] ` <20201229100639.2086-1-hdanton@sina.com>
2020-12-29 10:13 ` Lai Jiangshan
2021-01-08 11:46 ` [PATCH -tip V3 0/8] workqueue: break affinity initiatively Peter Zijlstra
2021-01-11 10:07 ` Thomas Gleixner
2021-01-11 11:01 ` Peter Zijlstra
2021-01-11 15:00 ` Paul E. McKenney
2021-01-11 17:16 ` Peter Zijlstra
2021-01-11 18:09 ` Paul E. McKenney
2021-01-11 21:50 ` Paul E. McKenney
2021-01-12 17:14 ` Paul E. McKenney
2021-01-12 23:53 ` Paul E. McKenney
2021-01-15 9:11 ` Peter Zijlstra
2021-01-15 13:04 ` Peter Zijlstra
2021-01-16 6:00 ` Lai Jiangshan
2021-01-11 19:21 ` Valentin Schneider
2021-01-11 20:23 ` Peter Zijlstra
2021-01-11 22:47 ` Valentin Schneider
2021-01-12 4:33 ` Lai Jiangshan
2021-01-12 14:53 ` Peter Zijlstra
2021-01-12 15:38 ` Lai Jiangshan
2021-01-13 11:10 ` Peter Zijlstra
2021-01-13 12:00 ` Lai Jiangshan
2021-01-13 12:57 ` Lai Jiangshan
2021-01-12 17:52 ` Valentin Schneider
2021-01-12 14:57 ` Jens Axboe
2021-01-12 15:51 ` Peter Zijlstra
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