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

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Message-ID: <20130430170027.GA28380@redhat.com>
Date:	Tue, 30 Apr 2013 19:00:27 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Colin Cross <ccross@...roid.com>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Arve Hjønnevåg <arve@...roid.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Serge Hallyn <serge.hallyn@...onical.com>
Subject: Re: [PATCH 09/10] sigtimedwait: use freezable blocking call

On 04/30, Colin Cross wrote:
> On Tue, Apr 30, 2013 at 9:38 AM, Oleg Nesterov <oleg@...hat.com> 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.
>
> See http://marc.info/?l=linux-pm&m=136727197819593&w=2 for the full
> justification.  I will include a fuller description of the reason for
> this patch in the next version.

Yes, thanks, I already realized what are you trying to do.

> > The task will be interrupted anyway and the syscall will return
> > -EAGAIN, this only changes the time when try_to_freeze() is called.
> >
> > For what? The task will call do_signal/try_to_freeze really "soon".
>
> See http://marc.info/?l=linux-pm&m=136727204919622&w=2, which removes
> the wakeup sent to skipped tasks, so schedule_timeout_interruptible()
> will only return if the timeout finishes or another task

Or if freeze_task() was already called.

but I guess you do not care.

Oleg.

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