From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
paulmck <paulmck@linux.ibm.com>, Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
"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>
Subject: Re: [RFC PATCH 4/4] Fix: sched/membarrier: p->mm->membarrier_state racy load (v2)
Date: Fri, 13 Sep 2019 11:20:56 -0400 (EDT) [thread overview]
Message-ID: <1629045844.2645.1568388056947.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <20190909110036.GC6719@redhat.com>
----- On Sep 9, 2019, at 7:00 AM, Oleg Nesterov oleg@redhat.com wrote:
> On 09/08, Mathieu Desnoyers wrote:
>>
>> +static void sync_runqueues_membarrier_state(struct mm_struct *mm)
>> +{
>> + int membarrier_state = atomic_read(&mm->membarrier_state);
>> + bool fallback = false;
>> + cpumask_var_t tmpmask;
>> + int cpu;
>> +
>> + if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) {
>> + WRITE_ONCE(this_rq()->membarrier_state, membarrier_state);
>
> This doesn't look safe, this caller can migrate to another CPU after
> it calculates the per-cpu ptr.
>
> I think you need do disable preemption or simply use this_cpu_write().
Good point! I'll use this_cpu_write() there and within
membarrier_exec_mmap(), which seems to be affected by the same problem.
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2019-09-13 15:21 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-06 3:12 [RFC PATCH 0/4] Membarrier fixes/cleanups Mathieu Desnoyers
2019-09-06 3:12 ` [RFC PATCH 1/4] Fix: sched/membarrier: private expedited registration check Mathieu Desnoyers
2019-09-06 3:12 ` [RFC PATCH 2/4] Cleanup: sched/membarrier: remove redundant check Mathieu Desnoyers
2019-09-06 3:12 ` [RFC PATCH 3/4] Cleanup: sched/membarrier: only sync_core before usermode for same mm Mathieu Desnoyers
2019-09-06 7:41 ` Peter Zijlstra
2019-09-06 13:40 ` Mathieu Desnoyers
2019-09-06 3:13 ` [RFC PATCH 4/4] Fix: sched/membarrier: p->mm->membarrier_state racy load Mathieu Desnoyers
2019-09-06 8:23 ` Peter Zijlstra
2019-09-08 13:49 ` [RFC PATCH 4/4] Fix: sched/membarrier: p->mm->membarrier_state racy load (v2) Mathieu Desnoyers
2019-09-08 16:51 ` Linus Torvalds
2019-09-10 9:48 ` Mathieu Desnoyers
2019-09-12 13:48 ` Will Deacon
2019-09-12 14:24 ` Linus Torvalds
2019-09-12 15:47 ` Will Deacon
2019-09-13 14:22 ` Mathieu Desnoyers
2019-09-19 16:26 ` Will Deacon
2019-09-19 17:33 ` Mathieu Desnoyers
2019-09-09 11:00 ` Oleg Nesterov
2019-09-13 15:20 ` Mathieu Desnoyers [this message]
2019-09-13 16:04 ` Oleg Nesterov
2019-09-13 17:07 ` Mathieu Desnoyers
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