Re: [PATCH RT 4/2] hrtimer: Don't lose state in cpu_chill()

[Sebastian Andrzej Siewior]

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