linux-kernel - [PATCH] PM-runtime: fix deadlock when canceling hrtimer

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Message-Id: <1550735942-3569-1-git-send-email-vincent.guittot@linaro.org>
Date:   Thu, 21 Feb 2019 08:59:02 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rjw@...ysocki.net, ulf.hansson@...aro.org
Cc:     sunzhaosheng@...ilicon.com,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH] PM-runtime: fix deadlock when canceling hrtimer

When rpm_resume() desactivates the autosuspend timer, it should only try
to cancel hrtimer but not wait for the handler to finish because both
rpm_resume() and pm_suspend_timer_fn() are taking the power.lock.
We can have the deadlock sequence:
CPU0                              CPU1
rpm_resume()
  spin_lock_irqsave
                                  pm_suspend_timer_fn()
                                    spin_lock_irqsave
  pm_runtime_deactivate_timer()
    hrtimer_cancel()

hrtimer_try_to_cancel() is enough because dev->power.timer_expires is also
set to 0.

Fixes: 8234f6734c5d ("PM-runtime: Switch autosuspend over to using hrtimers")
Reported-by: Sunzhaosheng Sun(Zhaosheng) <sunzhaosheng@...ilicon.com>
Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 drivers/base/power/runtime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index 04407d9..78937c4 100644
--- a/drivers/base/power/runtime.c
+++ b/drivers/base/power/runtime.c
@@ -121,7 +121,7 @@ EXPORT_SYMBOL_GPL(pm_runtime_suspended_time);
 static void pm_runtime_deactivate_timer(struct device *dev)
 {
 	if (dev->power.timer_expires > 0) {
-		hrtimer_cancel(&dev->power.suspend_timer);
+		hrtimer_try_to_cancel(&dev->power.suspend_timer);
 		dev->power.timer_expires = 0;
 	}
 }
-- 
2.7.4