linux-kernel - Re: [RFC][PATCH 08/11] sched: send SIGXCPU at -deadline task overruns.

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Date:	Tue, 13 Apr 2010 21:32:01 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Raistlin <raistlin@...ux.it>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Chris Friesen <cfriesen@...tel.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Darren Hart <darren@...art.com>,
	Henrik Austad <henrik@...tad.us>,
	Johan Eker <johan.eker@...csson.com>,
	"p.faure" <p.faure@...tech.ch>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Claudio Scordino <claudio@...dence.eu.com>,
	michael trimarchi <trimarchi@...is.sssup.it>,
	Fabio Checconi <fabio@...dalf.sssup.it>,
	Tommaso Cucinotta <t.cucinotta@...up.it>,
	Juri Lelli <juri.lelli@...il.com>,
	Nicola Manica <nicola.manica@...il.com>,
	Luca Abeni <luca.abeni@...tn.it>
Subject: Re: [RFC][PATCH 08/11] sched: send SIGXCPU at -deadline task
	overruns.

On 04/13, Peter Zijlstra wrote:
>
> On Sun, 2010-02-28 at 20:24 +0100, Raistlin wrote:
> >
> > +#define dl_se_signal(se, s, msg)					\
> > + do {									\
> > +  struct task_struct *t = dl_task_of(se);				\
> > +  sigaddset(&t->pending.signal, s);					\
> > +  set_tsk_thread_flag(t, TIF_SIGPENDING);				\
> > +  printk(KERN_INFO msg "in %d (%s)\n", task_pid_nr(t), t->comm);	\
> > + } while (0)
> > +

Without ->siglock?

This is racy even if dl_task_of(se) == current, but I guess it can
be !current. For example, we must never set TIF_SIGPENDING without
wake_up_state(). A fatal signal should kill the whole process, etc.
Even sigaddset() itself can race with tkill, it is not atomic.

Oleg.

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