linux-kernel - Re: [PATCH 1/1] signal: make group kill signal fatal

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Date:	Tue, 26 May 2009 00:51:50 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, ebiederm@...ssion.com,
	roland@...hat.com, linux-kernel@...r.kernel.org,
	Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH 1/1] signal: make group kill signal fatal

On 05/25, Jiri Slaby wrote:
>
> On 05/25/2009 07:20 PM, Oleg Nesterov wrote:
> > On 05/25, Jiri Slaby wrote:
> >> If the poll isn't there, it works well.
> >
> > Hmm. this is strange. Do you mean that if this program does
> > sleep(10000) (or something else) instead of poll() above, it
> > prints pend != 0 ?
>
> No, only when there is nothing, i.e. when it directly calls close. It's
> consistent with what you wrote. When there is sleep(), it works the same
> as the poll case.

Good ;)

> > And. Why do you need fatal_signal_pending() ? It is special,
> > should be used by things like wait_event_killable().
>
> I need to wait for a device to finish its work in last release, but also
> want to allow user to kill the waiting by SIGKILL if he thinks the
> device locked up (this is pretty usual for that particular device). If I
> use wait_event_killable, I end up with this.

Heh. In this case you have another (long-standing) issue, please note
the "if (p->flags & PF_EXITING)" check in wants_signal().

There is no guarantee the signal will wake up the exiting task task.
Even SIGKILL, even if you use wait_event_interruptible() instead of
_killable.

Oleg.

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