linux-kernel - [PATCH RT 10/30] hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration

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Date:   Thu, 23 Jan 2020 15:39:40 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        John Kacur <jkacur@...hat.com>,
        Julia Cartwright <julia@...com>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>,
        Julien Grall <julien.grall@....com>
Subject: [PATCH RT 10/30] hrtimer: Prevent using hrtimer_grab_expiry_lock() on migration_base

4.19.94-rt39-rc2 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Julien Grall <julien.grall@....com>

[ Upstream commit cef1b87f98823af923a386f3f69149acb212d4a1 ]

As tglx puts it:
|If base == migration_base then there is no point to lock soft_expiry_lock
|simply because the timer is not executing the callback in soft irq context
|and the whole lock/unlock dance can be avoided.

Furthermore, all the path leading to hrtimer_grab_expiry_lock() assumes
timer->base and timer->base->cpu_base are always non-NULL. So it is safe
to remove the NULL checks here.

Signed-off-by: Julien Grall <julien.grall@....com>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908211557420.2223@nanos.tec.linutronix.de
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
[bigeasy: rewrite changelog]
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 49d20fe8570f..1a5167c68310 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -943,7 +943,7 @@ void hrtimer_grab_expiry_lock(const struct hrtimer *timer)
 {
 	struct hrtimer_clock_base *base = READ_ONCE(timer->base);
 
-	if (timer->is_soft && base && base->cpu_base) {
+	if (timer->is_soft && base != &migration_base) {
 		spin_lock(&base->cpu_base->softirq_expiry_lock);
 		spin_unlock(&base->cpu_base->softirq_expiry_lock);
 	}
-- 
2.24.1