From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: paulmck <paulmck@linux.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Oleg Nesterov <oleg@redhat.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
"Russell King, ARM Linux" <linux@armlinux.org.uk>,
Chris Metcalf <cmetcalf@ezchip.com>, Chris Lameter <cl@linux.com>,
Kirill Tkhai <tkhai@yandex.ru>, Mike Galbraith <efault@gmx.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>
Subject: Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load
Date: Wed, 4 Sep 2019 13:49:29 +0200 [thread overview]
Message-ID: <20190904114929.GV2386@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190904112819.GD2349@hirez.programming.kicks-ass.net>
On Wed, Sep 04, 2019 at 01:28:19PM +0200, Peter Zijlstra wrote:
> @@ -196,6 +198,17 @@ static int membarrier_register_global_expedited(void)
> */
> smp_mb();
> } else {
> + struct task_struct *g, *t;
> +
> + read_lock(&tasklist_lock);
> + do_each_thread(g, t) {
> + if (t->mm == mm) {
> + atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED,
> + &t->membarrier_state);
> + }
> + } while_each_thread(g, t);
> + read_unlock(&tasklist_lock);
> +
> /*
> * For multi-mm user threads, we need to ensure all
> * future scheduler executions will observe the new
Arguably, because this is exposed to unpriv users and a potential
preemption latency issue, we could do it in 3 passes:
- RCU, mark all found lacking, count
- RCU, mark all found lacking, count
- if count of last pass, tasklist_lock
That way, it becomes much harder to trigger the bad case.
Do we worry about that?
next prev parent reply other threads:[~2019-09-04 11:49 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-03 20:11 [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load Mathieu Desnoyers
2019-09-03 20:11 ` [RFC PATCH 2/2] Fix: sched/membarrier: private expedited registration check Mathieu Desnoyers
2019-09-03 20:24 ` [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load Peter Zijlstra
2019-09-03 20:36 ` Linus Torvalds
2019-09-04 15:19 ` Mathieu Desnoyers
2019-09-04 16:09 ` Peter Zijlstra
2019-09-04 17:12 ` Mathieu Desnoyers
2019-09-04 18:26 ` Peter Zijlstra
2019-09-06 0:51 ` Mathieu Desnoyers
2019-09-03 20:41 ` Mathieu Desnoyers
2019-09-04 11:28 ` Peter Zijlstra
2019-09-04 11:49 ` Peter Zijlstra [this message]
2019-09-04 15:26 ` Mathieu Desnoyers
2019-09-04 12:03 ` Oleg Nesterov
2019-09-04 12:43 ` Peter Zijlstra
2019-09-04 13:17 ` Oleg Nesterov
2019-09-03 20:27 ` Linus Torvalds
2019-09-03 20:53 ` Mathieu Desnoyers
2019-09-04 10:53 ` Oleg Nesterov
2019-09-04 11:39 ` Peter Zijlstra
2019-09-04 15:24 ` Mathieu Desnoyers
2019-09-04 11:11 ` Oleg Nesterov
2019-09-04 16:11 ` Mathieu Desnoyers
2019-09-08 13:46 ` Mathieu Desnoyers
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