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

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Date:	Tue, 24 Jul 2007 20:48:36 +0200
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Pavel Machek <pavel@....cz>
CC:	"Rafael J. Wysocki" <rjw@...k.pl>, 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?

> 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.

--
	Manfred


View attachment "patch-poll-ERESTARTNOHAND" of type "text/plain" (783 bytes)

View attachment "sp.cpp" of type "text/x-c++src" (790 bytes)