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SubjectRe: [PATCH RT 4/2] hrtimer: Don't lose state in cpu_chill()
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Hi Sebastian,

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.

On Tue, 2019-02-19 at 17:08 +0100, Sebastian Andrzej Siewior wrote:
> In cpu_chill() the state is set to TASK_UNINTERRUPTIBLE and a timer is
> programmed. On return the state is always TASK_RUNNING which means we
> lose the state if it was something other than RUNNING. Also
> set_current_state() sets ->task_state_change to within cpu_chill() which
> is not expected.
>
> Save the task state on entry and restore it on return. Simply set the
> state in order to avoid updating ->task_state_change.
>
> Cc: stable-rt@vger.kernel.org
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
> kernel/time/hrtimer.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
> index 851b2134e77f4..6f2736ec4b8ef 100644
> --- a/kernel/time/hrtimer.c
> +++ b/kernel/time/hrtimer.c
> @@ -1902,15 +1902,18 @@ void cpu_chill(void)
> {
> 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);
> - set_current_state(TASK_UNINTERRUPTIBLE);
> + __set_current_state_no_track(TASK_UNINTERRUPTIBLE);
> 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);
> }
> EXPORT_SYMBOL(cpu_chill);
> #endif

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