Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup

[Andrea Parri]

On Thu, Apr 26, 2018 at 10:41:31AM +0200, Peter Zijlstra wrote:

[...]

> +/*
> + * Special states are those that do not use the normal wait-loop pattern. See
> + * the comment with set_special_state().
> + */
> +#define is_special_state(state)              \
> +     ((state) == TASK_DEAD ||        \
> +      (state) == TASK_STOPPED)
> +
>  #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
>  
> +/*
> + * Assert we don't use the regular *set_current_state() helpers for special
> + * states. See the comment with set_special_state().
> + */
> +#define assert_special_state(state)  WARN_ON_ONCE(is_special_state(state))

Nitpicking, this name suggests "Shout if the state is NOT special" to me:
maybe,

#define assert_special_state(state)     WARN_ON_ONCE(!is_special_state(state))
#define assert_regular_state(state)     WARN_ON_ONCE(is_special_state(state))

or just do with the WARN_ON_ONCE()s ?

  Andrea


> +
>  #define __set_current_state(state_value)                     \
>       do {                                                    \
> +             assert_special_state(state_value);              \
>               current->task_state_change = _THIS_IP_;         \
>               current->state = (state_value);                 \
>       } while (0)
> +
>  #define set_current_state(state_value)                               \
>       do {                                                    \
> +             assert_special_state(state_value);              \
>               current->task_state_change = _THIS_IP_;         \
>               smp_store_mb(current->state, (state_value));    \
>       } while (0)
>  
> +#define set_special_state(state_value)                                       
> \
> +     do {                                                            \
> +             unsigned long flags; /* may shadow */                   \
> +             WARN_ON_ONCE(!is_special_state(state_value));           \
> +             raw_spin_lock_irqsave(&current->pi_lock, flags);        \
> +             current->task_state_change = _THIS_IP_;                 \
> +             current->state = (state_value);                         \
> +             raw_spin_unlock_irqrestore(&current->pi_lock, flags);   \
> +     } while (0)