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

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Date:   Tue, 6 Sep 2022 13:08:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.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()

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.
  */
 #define wait_event_state(wq_head, condition, state)				\
 ({										\


> > +#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.

Yeah, I'm going to leave it as is.