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

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Message-ID: <YxhHknM8n/b3W7wr@gmail.com>
Date:   Wed, 7 Sep 2022 09:26:10 +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:

> On Sun, Sep 04, 2022 at 11:54:57AM +0200, Ingo Molnar wrote:
> > > +/**
> > > + * 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.
> 
> 
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -942,14 +942,14 @@ extern int do_wait_intr_irq(wait_queue_h
>   * @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.
> + * or a signal is received (when allowed by @state).  The @condition is checked
> + * each time the waitqueue @wq_head is woken up.
>   *
>   * 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.
> + * The function will return -ERESTARTSYS if it was interrupted by a signal
> + * (when allowed by @state) and 0 if @condition evaluated to true.
>   */

Reviewed-by: Ingo Molnar <mingo@...nel.org>

> > > +#define wait_event_state(wq_head, condition, state)				\
> > > +({										\
> > > +	int __ret = 0;								\
> > > +                                                                             \
> > > +	might_sleep();								\
> > 
> > Like most (but not all ... :-/ ) of the existing primitives have.
> 
> Yeah, I'm going to leave it as is.

Will queue up a cleanup patch, should I ever notice this detail again ... :-)

Thanks,

	Ingo