From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Chris Metcalf <cmetcalf@ezchip.com>,
Christoph 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: Tue, 3 Sep 2019 22:24:34 +0200 [thread overview]
Message-ID: <20190903202434.GX2349@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190903201135.1494-1-mathieu.desnoyers@efficios.com>
On Tue, Sep 03, 2019 at 04:11:34PM -0400, Mathieu Desnoyers wrote:
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 9f51932bd543..e24d52a4c37a 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1130,6 +1130,10 @@ struct task_struct {
> unsigned long numa_pages_migrated;
> #endif /* CONFIG_NUMA_BALANCING */
>
> +#ifdef CONFIG_MEMBARRIER
> + atomic_t membarrier_state;
> +#endif
> +
> #ifdef CONFIG_RSEQ
> struct rseq __user *rseq;
> u32 rseq_sig;
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 4a7944078cc3..3577cd7b3dbb 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -371,7 +371,17 @@ static inline void membarrier_mm_sync_core_before_usermode(struct mm_struct *mm)
> static inline void membarrier_execve(struct task_struct *t)
> {
> atomic_set(&t->mm->membarrier_state, 0);
> + atomic_set(&t->membarrier_state, 0);
> }
> +
> +static inline void membarrier_prepare_task_switch(struct task_struct *t)
> +{
> + if (!t->mm)
> + return;
> + atomic_set(&t->membarrier_state,
> + atomic_read(&t->mm->membarrier_state));
> +}
> +
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 010d578118d6..8d4f1f20db15 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3038,6 +3038,7 @@ prepare_task_switch(struct rq *rq, struct task_struct *prev,
> perf_event_task_sched_out(prev, next);
> rseq_preempt(prev);
> fire_sched_out_preempt_notifiers(prev, next);
> + membarrier_prepare_task_switch(next);
> prepare_task(next);
> prepare_arch_switch(next);
> }
Yuck yuck yuck..
so the problem I have with this is that we add yet another cacheline :/
Why can't we frob this state into a line/word we already have to
unconditionally touch, like the thread_info::flags word for example.
The above also does the store unconditionally, even though, in the most
common case, it won't have to.
next prev parent reply other threads:[~2019-09-03 20:25 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 ` Peter Zijlstra [this message]
2019-09-03 20:36 ` [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load 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
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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