linux-kernel - Re: which signal is sent to freeze process?

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Message-Id: <200707252119.33285.rjw@sisk.pl>
Date:	Wed, 25 Jul 2007 21:19:32 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	Pavel Machek <pavel@....cz>, linux-kernel@...r.kernel.org,
	"Agarwal, Lomesh" <lomesh.agarwal@...el.com>,
	Nigel Cunningham <nigel@...el.suspend2.net>
Subject: Re: which signal is sent to freeze process?

On Tuesday, 24 July 2007 20:48, Manfred Spraul wrote:
> > Hi!
> >
> > Can you generate small testcase that demonstrates the problem?
> >
> > > Then what would be the correct way to handle resume process. The other
> > > way of course is to make all the applications check the errno in case of
> > > failure. But that seems more more problematic then system call checking.
> > > What do you say?
> >
> > Hmm, does that testcase behave correctly over SIGSTOP/SIGCONT? I'm not
> > saying kernel behaves nicely here, but perhaps fixing the apps to
> > check errno properly is the right thing to do? :-)
> Perhaps the kernel should use ERESTARTNOHAND instead of EINTR?
> The current code is more than odd:
> - select() and sys_ppoll() both use ERESTARTNOHAND (i.e.: 
> the functions do not return to user space with SIGSTOP/SIGCONT or freezer())
> 
> - sys_poll() uses EINTR (i.e.: SIGSTOP/SIGCONT/freezer() return to user space)
> 
> Attached is a patch that switches sys_poll to ERESTARTNOHAND and a poll test app.
> Boot tested with FC6.
> 
> What do you think? With ERESTARTNOHAND, poll would only return to user space if the app has a SIGCONT handler installed.

Well, I don't know why sys_poll() uses EINTR, so I don't know if that's not for
a reason.  Using ERESTARTNOHAND instead of it seems to be a good idea, though.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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