linux-kernel - [PATCH 10/13] hrtimer: cpu_chill(): save task state in ->saved

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Message-Id: <0f9545ca84d4d0ec5bedd2b36a4fda0871fad244.1554737688.git.tom.zanussi@linux.intel.com>
Date:   Mon,  8 Apr 2019 14:14:12 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Cc:     rostedt@...dmis.org, tglx@...utronix.de, C.Emde@...dl.org,
        jkacur@...hat.com, bigeasy@...utronix.de,
        daniel.wagner@...mens.com, julia@...com, amartin@...dia.com
Subject: [PATCH 10/13] hrtimer: cpu_chill(): save task state in ->saved_state()

4.14.109-rt58-rc1 stable review patch.
If anyone has any objections, please let me know.

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

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

[ Upstream commit d70f218ee02d6fc3832274653aa6c6e98dd9aa43 ]

In the previous change I saved the current task state on stack. This was
bad because while the task is scheduled-out it might receive a wake-up.
The wake up changes the task state and we must not destroy it.

Save the task-state in ->saved_state under a PI-lock to unsure that
state changes during are not missed while the task temporary scheduled
out.

Reported-by: Mike Galbraith <efault@....de>
Tested-by: Mike Galbraith <efault@....de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Tom Zanussi <tom.zanussi@...ux.intel.com>
---
 kernel/time/hrtimer.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 6da6b5dded3c..9990b567b089 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1864,20 +1864,28 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct compat_timespec __user *, rqtp,
  */
 void cpu_chill(void)
 {
-	ktime_t chill_time;
 	unsigned int freeze_flag = current->flags & PF_NOFREEZE;
-	long saved_state;
+	struct task_struct *self = current;
+	ktime_t chill_time;
 
-	saved_state = current->state;
-	chill_time = ktime_set(0, NSEC_PER_MSEC);
+	raw_spin_lock_irq(&self->pi_lock);
+	self->saved_state = self->state;
 	__set_current_state_no_track(TASK_UNINTERRUPTIBLE);
+	raw_spin_unlock_irq(&self->pi_lock);
+
+	chill_time = ktime_set(0, NSEC_PER_MSEC);
+
 	current->flags |= PF_NOFREEZE;
 	sleeping_lock_inc();
 	schedule_hrtimeout(&chill_time, HRTIMER_MODE_REL_HARD);
 	sleeping_lock_dec();
 	if (!freeze_flag)
 		current->flags &= ~PF_NOFREEZE;
-	__set_current_state_no_track(saved_state);
+
+	raw_spin_lock_irq(&self->pi_lock);
+	__set_current_state_no_track(self->saved_state);
+	self->saved_state = TASK_RUNNING;
+	raw_spin_unlock_irq(&self->pi_lock);
 }
 EXPORT_SYMBOL(cpu_chill);
 #endif
-- 
2.14.1