linux-kernel - [PATCH] sched/membarrier: fix missing local execution of ipi_sync_rq

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Date:   Wed, 17 Feb 2021 11:56:51 -0500
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Nadav Amit <nadav.amit@...il.com>, stable@...r.kernel.org
Subject: [PATCH] sched/membarrier: fix missing local execution of ipi_sync_rq_state()

The function sync_runqueues_membarrier_state() should copy the
membarrier state from the @mm received as parameter to each runqueue
currently running tasks using that mm.

However, the use of smp_call_function_many() skips the current runqueue,
which is unintended. Replace by a call to on_each_cpu_mask().

Fixes: 227a4aadc75b ("sched/membarrier: Fix p->mm->membarrier_state racy load")
Link: https://lore.kernel.org/r/74F1E842-4A84-47BF-B6C2-5407DFDD4A4A@gmail.com
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Reported-by: Nadav Amit <nadav.amit@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Nadav Amit <nadav.amit@...il.com>
Cc: stable@...r.kernel.org # 5.4.x+
---
 kernel/sched/membarrier.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 08ae45ad9261..f311bf85d211 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -471,9 +471,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm)
 	}
 	rcu_read_unlock();
 
-	preempt_disable();
-	smp_call_function_many(tmpmask, ipi_sync_rq_state, mm, 1);
-	preempt_enable();
+	on_each_cpu_mask(tmpmask, ipi_sync_rq_state, mm, true);
 
 	free_cpumask_var(tmpmask);
 	cpus_read_unlock();
-- 
2.17.1