linux-kernel - Re: [PATCH RT 4/2] hrtimer: Don't lose state in cpu

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Date:   Mon, 25 Feb 2019 17:34:40 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Mike Galbraith <efault@....de>
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH RT 4/2] hrtimer: Don't lose state in cpu_chill()

On 2019-02-25 15:43:35 [+0100], Mike Galbraith wrote:
> Hi Sebastian,
Hi Mike,

> My box claims that this patch is busted.  It argues its case by IO
> deadlocking any kernel this patch is applied to when spinning rust is
> flogged, including virgin 4.19-rt14, said kernel becoming stable again
> when I whack the accused.

does the following hunk make any difference?

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 6ecdb9469ca9..e154632b90b4 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1884,20 +1884,29 @@ COMPAT_SYSCALL_DEFINE2(nanosleep, struct old_timespec32 __user *, rqtp,
  */
 void cpu_chill(void)
 {
+	struct task_struct *self = current;
 	ktime_t chill_time;
 	unsigned int freeze_flag = current->flags & PF_NOFREEZE;
-	long saved_state;
 
-	saved_state = current->state;
-	chill_time = ktime_set(0, NSEC_PER_MSEC);
+	raw_spin_lock_irq(&self->pi_lock);
+	WARN_ON(self->saved_state != TASK_RUNNING);
+	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

Sebastian