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From: Valentin Schneider <vschneid@redhat.com>
To: Wander Lairson Costa <wander@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Stafford Horne <shorne@gmail.com>,
	Kefeng Wang <wangkefeng.wang@huawei.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Andy Lutomirski <luto@kernel.org>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Andrei Vagin <avagin@gmail.com>,
	open list <linux-kernel@vger.kernel.org>,
	Paul McKenney <paulmck@kernel.org>
Subject: Re: [PATCH v2 1/4] sched/task: Add the put_task_struct_atomic_safe function
Date: Mon, 30 Jan 2023 14:46:54 +0000	[thread overview]
Message-ID: <xhsmh357sdqqp.mognet@vschneid.remote.csb> (raw)
In-Reply-To: <CAAq0SUnUH6DEjwEs2RxRCtkTU121JXpdsV_rZky1d0Bo04=fiQ@mail.gmail.com>

On 30/01/23 08:49, Wander Lairson Costa wrote:
> On Fri, Jan 27, 2023 at 12:55 PM Valentin Schneider <vschneid@redhat.com> wrote:
>>
>> On 23/01/23 14:24, Wander Lairson Costa wrote:
>> > Therefore (if I am correct in my assumption), it would make sense for
>> > only some call sites to pay the overhead price for it. But this is
>> > just a guess, and I have no evidence to support my claim.
>>
>> My worry here is that it's easy to miss problematic callgraphs, and it's
>> potentially easy for new ones to creep in. Having a solution within
>> put_task_struct() itself would prevent that.
>>
>
> We could add a WARN_ON statement in put_task_struct() to detect such cases.
>

Anyone running their kernel with DEBUG_ATOMIC_SLEEP should be able to
detect misuse, but it doesn't change that some callgraphs will only
materialize under certain hardware/configuration combos.

>> Another thing, if you look at release_task_stack(), it either caches the
>> outgoing stack for later use, or frees it via RCU (regardless of
>> PREEMPT_RT). Perhaps we could follow that and just always punt the freeing
>> of the task struct to RCU?
>>
>
> That's a point. Do you mean doing that even for !PREEMPT_RT?

Could be worth a try? I think because of the cache thing the task stack is
a bit less aggressive wrt RCU callback processing, but at a quick glance I
don't see any fundamental reason why the task_struct itself can't be given
the same treatment.


  reply	other threads:[~2023-01-30 14:47 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-20 15:02 [PATCH v2 0/4] Fix put_task_struct() calls under PREEMPT_RT Wander Lairson Costa
2023-01-20 15:02 ` [PATCH v2 1/4] sched/task: Add the put_task_struct_atomic_safe function Wander Lairson Costa
2023-01-23 16:30   ` Oleg Nesterov
2023-01-23 16:49     ` Oleg Nesterov
2023-01-23 17:24     ` Wander Lairson Costa
2023-01-27 15:55       ` Valentin Schneider
2023-01-30 11:49         ` Wander Lairson Costa
2023-01-30 14:46           ` Valentin Schneider [this message]
2023-01-30 14:58             ` Wander Lairson Costa
2023-01-30 15:20               ` Valentin Schneider
2023-02-17 17:35           ` Daniel Bristot de Oliveira
2023-02-17 19:04             ` luca abeni
2023-02-22 18:42               ` Wander Lairson Costa
2023-02-22 21:00                 ` luca abeni
2023-02-24  8:46                   ` luca abeni
2023-02-24 13:02                     ` Wander Lairson Costa
2023-02-24 16:01                       ` luca abeni
2023-01-20 15:02 ` [PATCH v2 2/4] sched/deadline: fix inactive_task_timer splat Wander Lairson Costa
2023-01-20 15:02 ` [PATCH v2 3/4] sched/rt: use put_task_struct_atomic_safe() to avoid potential splat Wander Lairson Costa
2023-01-25  0:16   ` Steven Rostedt
2023-01-20 15:02 ` [PATCH v2 4/4] sched/core: " Wander Lairson Costa
2023-01-20 17:45 ` [PATCH v2 0/4] Fix put_task_struct() calls under PREEMPT_RT Valentin Schneider
2023-01-20 20:14   ` Wander Lairson Costa

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