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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: [PATCH 1/3] sched: fix exit_mm vs membarrier (v4)
Date: Tue, 20 Oct 2020 16:36:48 +0200	[thread overview]
Message-ID: <20201020143648.GU2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201020134715.13909-2-mathieu.desnoyers@efficios.com>

On Tue, Oct 20, 2020 at 09:47:13AM -0400, Mathieu Desnoyers wrote:
> +void membarrier_update_current_mm(struct mm_struct *next_mm)
> +{
> +	struct rq *rq = this_rq();
> +	int membarrier_state = 0;
> +
> +	if (next_mm)
> +		membarrier_state = atomic_read(&next_mm->membarrier_state);
> +	if (READ_ONCE(rq->membarrier_state) == membarrier_state)
> +		return;
> +	WRITE_ONCE(rq->membarrier_state, membarrier_state);
> +}

This is suspisioucly similar to membarrier_switch_mm().

Would something like so make sense?

---
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -206,14 +206,7 @@ void membarrier_exec_mmap(struct mm_stru
 
 void membarrier_update_current_mm(struct mm_struct *next_mm)
 {
-	struct rq *rq = this_rq();
-	int membarrier_state = 0;
-
-	if (next_mm)
-		membarrier_state = atomic_read(&next_mm->membarrier_state);
-	if (READ_ONCE(rq->membarrier_state) == membarrier_state)
-		return;
-	WRITE_ONCE(rq->membarrier_state, membarrier_state);
+	membarrier_switch_mm(this_rq(), NULL, next_mm);
 }
 
 static int membarrier_global_expedited(void)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d2621155393c..3d589c2ffd28 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2645,12 +2645,14 @@ static inline void membarrier_switch_mm(struct rq *rq,
 					struct mm_struct *prev_mm,
 					struct mm_struct *next_mm)
 {
-	int membarrier_state;
+	int membarrier_state = 0;
 
 	if (prev_mm == next_mm)
 		return;
 
-	membarrier_state = atomic_read(&next_mm->membarrier_state);
+	if (next_mm)
+		membarrier_state = atomic_read(&next_mm->membarrier_state);
+
 	if (READ_ONCE(rq->membarrier_state) == membarrier_state)
 		return;
 

  reply	other threads:[~2020-10-20 14:37 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-20 13:47 [PATCH 0/3] Membarrier updates Mathieu Desnoyers
2020-10-20 13:47 ` [PATCH 1/3] sched: fix exit_mm vs membarrier (v4) Mathieu Desnoyers
2020-10-20 14:36   ` Peter Zijlstra [this message]
2020-10-20 14:59     ` Mathieu Desnoyers
2020-10-20 14:59       ` Mathieu Desnoyers
2020-10-22  6:51       ` Boqun Feng
2020-10-29 10:51   ` [tip: sched/core] " tip-bot2 for Mathieu Desnoyers
2020-10-20 13:47 ` [PATCH 2/3] sched: membarrier: cover kthread_use_mm (v4) Mathieu Desnoyers
2020-10-29 10:51   ` [tip: sched/core] " tip-bot2 for Mathieu Desnoyers
2020-10-20 13:47 ` [PATCH 3/3] sched: membarrier: document memory ordering scenarios Mathieu Desnoyers
2020-10-29 10:51   ` [tip: sched/core] " tip-bot2 for Mathieu Desnoyers

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