linux-kernel - Re: [PATCH v3 5/6] sched/wait: Add wait_event

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Message-ID: <YxR18Qs8vqTpPFV5@gmail.com>
Date:   Sun, 4 Sep 2022 11:54:57 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rjw@...ysocki.net, oleg@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, mgorman@...e.de,
        ebiederm@...ssion.com, bigeasy@...utronix.de,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        tj@...nel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 5/6] sched/wait: Add wait_event_state()


* Peter Zijlstra <peterz@...radead.org> wrote:

> Allows waiting with a custom @state.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  include/linux/wait.h |   28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -931,6 +931,34 @@ extern int do_wait_intr_irq(wait_queue_h
>  	__ret;									\
>  })
>  
> +#define __wait_event_state(wq, condition, state)				\
> +	___wait_event(wq, condition, state, 0, 0, schedule())
> +
> +/**
> + * wait_event_state - sleep until a condition gets true
> + * @wq_head: the waitqueue to wait on
> + * @condition: a C expression for the event to wait for
> + * @state: state to sleep in
> + *
> + * The process is put to sleep (@state) until the @condition evaluates to true
> + * or a signal is received.  The @condition is checked each time the waitqueue
> + * @wq_head is woken up.

Documentation inconsistency nit: if TASK_INTERRUPTIBLE isn't in @state then 
we won't wake up when a signal is received. This probably got copy-pasted 
from a signal variant.

> + *
> + * wake_up() has to be called after changing any variable that could
> + * change the result of the wait condition.
> + *
> + * The function will return -ERESTARTSYS if it was interrupted by a
> + * signal and 0 if @condition evaluated to true.

That's not unconditionally true either if !TASK_INTERRUPTIBLE.

> +#define wait_event_state(wq_head, condition, state)				\
> +({										\
> +	int __ret = 0;								\
> +	might_sleep();								\

Very small style consistency nit, the above should have a newline after 
local variables:

> +#define wait_event_state(wq_head, condition, state)				\
> +({										\
> +	int __ret = 0;								\
> +                                                                             \
> +	might_sleep();								\

Like most (but not all ... :-/ ) of the existing primitives have.

Thanks,

	Ingo