From: Oleg Nesterov <oleg@redhat.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Wander Lairson Costa <wander@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.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>,
Hu Chunyu <chuhu@redhat.com>,
Valentin Schneider <vschneid@redhat.com>,
Paul McKenney <paulmck@kernel.org>
Subject: Re: [PATCH v4] kernel/fork: beware of __put_task_struct calling context
Date: Mon, 6 Feb 2023 16:27:12 +0100 [thread overview]
Message-ID: <20230206152712.GA1487@redhat.com> (raw)
In-Reply-To: <Y+EVNz4ORkFSvTfP@linutronix.de>
On 02/06, Sebastian Andrzej Siewior wrote:
>
> On 2023-02-06 10:04:47 [-0300], Wander Lairson Costa wrote:
>
> > @@ -857,6 +857,29 @@ void __put_task_struct(struct task_struct *tsk)
> …
> > +void __put_task_struct(struct task_struct *tsk)
> > +{
> > + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (!preemptible() || !in_task()))
>
> Is it safe to use the rcu member in any case?
I thinks it is safe but deserves a comment. I guess Wander misunderstood
me when I asked him to do this...
__put_task_struct() is called when refcount_dec_and_test(&t->usage) succeeds.
This means that it can't "conflict" with put_task_struct_rcu_user() which
abuses ->rcu the same way; rcu_users has a reference so task->usage can't
be zero after rcu_users 1 -> 0 transition.
> If so why not use it
> unconditionally?
performance ?
And... I still don't like the name of delayed_put_task_struct_rcu() to me
___put_task_struct_rcu() looks a bit less confusing, note that we already
have delayed_put_task_struct(). But this is minor.
Oleg.
next prev parent reply other threads:[~2023-02-06 15:28 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-06 13:04 [PATCH v4] kernel/fork: beware of __put_task_struct calling context Wander Lairson Costa
2023-02-06 14:56 ` Sebastian Andrzej Siewior
2023-02-06 15:27 ` Oleg Nesterov [this message]
2023-02-06 16:04 ` Sebastian Andrzej Siewior
2023-02-06 16:27 ` Oleg Nesterov
2023-02-10 16:48 ` Sebastian Andrzej Siewior
2023-02-06 18:36 ` Wander Lairson Costa
2023-02-06 18:34 ` Wander Lairson Costa
2023-02-06 18:32 ` Wander Lairson Costa
2023-02-07 1:09 ` Andrew Morton
2023-02-07 15:26 ` Wander Lairson Costa
2023-02-10 17:08 ` Sebastian Andrzej Siewior
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