linux-kernel - Re: [PATCH 08/10] oom: use send_sig() instead force

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Message-Id: <20100613180912.617B.A69D9226@jp.fujitsu.com>
Date:	Sun, 13 Jun 2010 20:24:52 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>,
	Minchan Kim <minchan.kim@...il.com>
Subject: Re: [PATCH 08/10] oom: use send_sig() instead force_sig()

> On 06/08, KOSAKI Motohiro wrote:
> >
> > Oleg pointed out oom_kill.c has force_sig() abuse. force_sig() mean
> > ignore signal mask. but SIGKILL itself is not maskable.
> 
> Yes. And we have other reasons to avoid force_sig(). It should be used
> only for synchronous signals.
> 
> But,
> 
> > @@ -399,7 +399,7 @@ static int __oom_kill_process(struct task_struct *p, struct mem_cgroup *mem)
> >  	p->rt.time_slice = HZ;
> >  	set_tsk_thread_flag(p, TIF_MEMDIE);
> >
> > -	force_sig(SIGKILL, p);
> > +	send_sig(SIGKILL, p, 1);
> 
> This is not right, we need send_sig(SIGKILL, p, 0). Better yet,
> send_sig_info(SIGKILL, SEND_SIG_NOINFO). I think send_sig() should
> die.
> 
> The reason is that si_fromuser() must be true, otherwise we can't kill
> the SIGNAL_UNKILLABLE (sub-namespace inits) tasks.

Thanks. I am not signal expert. 
To be honest, current special siginfo arguments have a bit unclear meanings
to me ;)
current definition (following) doesn't teach anything.

sched.h
=====================
/* These can be the second arg to send_sig_info/send_group_sig_info.  */
#define SEND_SIG_NOINFO ((struct siginfo *) 0)
#define SEND_SIG_PRIV   ((struct siginfo *) 1)
#define SEND_SIG_FORCED ((struct siginfo *) 2)


If anyone write exact meanings, I'm really really glad.



> Oh. This reminds me, we really need the trivial (but annoying) cleanups
> here. The usage of SEND_SIG_ constants is messy, and they should be
> renamed at least.
> 
> And in fact, we need the new one which acts like SEND_SIG_FORCED but
> si_fromuser(). We do not want to allocate the memory when the caller
> is oom_kill or zap_pid_ns_processes().
> 
> OK. I'll send the simple patch which adds the new helper with the
> comment. send_sigkill() or kernel_kill_task(), or do you see a
> better name?

Very thanks. both name are pretty good to me.



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