Re: [PATCH 09/10] sigtimedwait: use freezable blocking call

From: Oleg Nesterov
Date: Tue Apr 30 2013 - 12:59:27 EST


On 04/30, Oleg Nesterov wrote:
>
> On 04/29, Colin Cross wrote:
> >
> > Avoid waking up every thread sleeping in a sigtimedwait call during
> > suspend and resume by calling a freezable blocking call.
>
> This doesn't explain why do want this change...
>
> OK, probably to avoid -EAGAIN from sigtimedwait() if the freezer wakes
> up the caller.
>
> > --- a/kernel/signal.c
> > +++ b/kernel/signal.c
> > @@ -2845,7 +2845,7 @@ int do_sigtimedwait(const sigset_t *which, siginfo_t *info,
> > recalc_sigpending();
> > spin_unlock_irq(&tsk->sighand->siglock);
> >
> > - timeout = schedule_timeout_interruptible(timeout);
> > + timeout = freezable_schedule_timeout_interruptible(timeout);
>
> And I guess freezable_schedule_timeout_interruptible() is added by
> http://marc.info/?l=linux-kernel&m=136727195719575 ...
>
> +#define freezable_schedule_timeout_interruptible(timeout) \
> +({ \
> + long __retval; \
> + freezer_do_not_count(); \
> + __retval = schedule_timeout_interruptible(timeout); \
> + freezer_count(); \
> + __retval; \
> +})
>
> How this can help?
>
> The task will be interrupted anyway and the syscall will return
> -EAGAIN, this only changes the time when try_to_freeze() is called.

OK, I wasn't cced, I have found another patch
http://marc.info/?l=linux-kernel&m=136727200519602 which should make
a difference, it won't be woken if PF_FREEZER_SKIP was already set.

This is racy, but it seems that "avoid -EAGAIN" was not your goal...

> For what? The task will call do_signal/try_to_freeze really "soon".

It seems that you want to speed up the freezing.

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/