linux-kernel - [PATCH] sched/core: idle_task_exit() shouldn't use switch_mm_irqs

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Message-Id: <ca3d1a9fa93a0b49f5a8ff729eda3640fb6abdf9.1497034141.git.luto@kernel.org>
Date:   Fri,  9 Jun 2017 11:49:15 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>, stable@...r.kernel.org,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] sched/core: idle_task_exit() shouldn't use switch_mm_irqs_off()

idle_task_exit() can be called with IRQs on x86 on and therefore
should use switch_mm(), not switch_mm_irqs_off().

This doesn't seem to cause any problems right now, but it will
confuse my upcoming TLB flush changes.  Nonetheless, I think it
should be backported because it's trivial.  There won't be any
meaningful performance impact because idle_task_exit() is only
used when offlining a CPU.

Cc: stable@...r.kernel.org
Fixes: f98db6013c55 ("sched/core: Add switch_mm_irqs_off() and use it in the scheduler")
Cc: Borislav Petkov <bp@...e.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 kernel/sched/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 803c3bc274c4..326d4f88e2b1 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5605,7 +5605,7 @@ void idle_task_exit(void)
 	BUG_ON(cpu_online(smp_processor_id()));
 
 	if (mm != &init_mm) {
-		switch_mm_irqs_off(mm, &init_mm, current);
+		switch_mm(mm, &init_mm, current);
 		finish_arch_post_lock_switch();
 	}
 	mmdrop(mm);
-- 
2.9.4