From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Boqun Feng <boqun.feng@gmail.com>,
linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>,
Nicholas Piggin <npiggin@gmail.com>,
Andy Lutomirski <luto@amacapital.net>,
Thomas Gleixner <tglx@linutronix.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Alan Stern <stern@rowland.harvard.edu>,
linux-mm@kvack.org
Subject: Re: [RFC PATCH 1/3] sched: fix exit_mm vs membarrier (v3)
Date: Wed, 7 Oct 2020 16:29:47 +0200 [thread overview]
Message-ID: <20201007142947.GG2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200924172508.8724-2-mathieu.desnoyers@efficios.com>
On Thu, Sep 24, 2020 at 01:25:06PM -0400, Mathieu Desnoyers wrote:
> diff --git a/kernel/exit.c b/kernel/exit.c
> index 733e80f334e7..0767a2dbf245 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -475,7 +475,19 @@ static void exit_mm(void)
> BUG_ON(mm != current->active_mm);
> /* more a memory barrier than a real lock */
> task_lock(current);
> + /*
> + * When a thread stops operating on an address space, the loop
> + * in membarrier_private_expedited() may not observe that
> + * tsk->mm, and the loop in membarrier_global_expedited() may
> + * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED
> + * rq->membarrier_state, so those would not issue an IPI.
> + * Membarrier requires a memory barrier after accessing
> + * user-space memory, before clearing tsk->mm or the
> + * rq->membarrier_state.
> + */
> + smp_mb__after_spinlock();
> current->mm = NULL;
> + membarrier_update_current_mm(NULL);
> mmap_read_unlock(mm);
> enter_lazy_tlb(mm, current);
> task_unlock(current);
This site seems to be lacking in IRQ disabling. As proposed it will
explode on RT.
Something like so to match kthread_unuse_mm().
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -486,11 +486,13 @@ static void exit_mm(void)
* rq->membarrier_state.
*/
smp_mb__after_spinlock();
+ local_irq_disable()
current->mm = NULL;
membarrier_update_current_mm(NULL);
- mmap_read_unlock(mm);
enter_lazy_tlb(mm, current);
+ local_irq_enable();
task_unlock(current);
+ mmap_read_unlock(mm);
mm_update_next_owner(mm);
mmput(mm);
if (test_thread_flag(TIF_MEMDIE))
next prev parent reply other threads:[~2020-10-07 14:30 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-24 17:25 [RFC PATCH 0/3] Membarrier updates Mathieu Desnoyers
2020-09-24 17:25 ` [RFC PATCH 1/3] sched: fix exit_mm vs membarrier (v3) Mathieu Desnoyers
2020-10-07 14:29 ` Peter Zijlstra [this message]
2020-10-07 14:57 ` Mathieu Desnoyers
2020-10-07 15:09 ` Peter Zijlstra
2020-09-24 17:25 ` [RFC PATCH 2/3] sched: membarrier: cover kthread_use_mm (v3) Mathieu Desnoyers
2020-10-02 8:33 ` [sched] bdfcae1140: will-it-scale.per_thread_ops -37.0% regression kernel test robot
2020-10-07 14:50 ` Mathieu Desnoyers
2020-10-20 3:24 ` [LKP] " Xing Zhengjun
2020-10-20 13:14 ` Mathieu Desnoyers
2020-10-22 1:54 ` Xing Zhengjun
2020-10-22 13:19 ` Mathieu Desnoyers
2020-10-23 5:37 ` Xing Zhengjun
2020-10-23 12:34 ` Mathieu Desnoyers
2020-10-07 15:07 ` [RFC PATCH 2/3] sched: membarrier: cover kthread_use_mm (v3) Peter Zijlstra
2020-10-07 15:39 ` Mathieu Desnoyers
2020-10-07 16:08 ` Peter Zijlstra
2020-10-07 16:11 ` Mathieu Desnoyers
2020-09-24 17:25 ` [RFC PATCH 3/3] sched: membarrier: document memory ordering scenarios Mathieu Desnoyers
2020-09-29 17:16 ` [RFC PATCH 0/3] Membarrier updates Mathieu Desnoyers
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