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From: Oleg Nesterov <oleg@tv-sign.ru>
To: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Alan Cox <alan@redhat.com>,
	Davide Libenzi <davidel@xmailserver.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Ingo Molnar <mingo@elte.hu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] orphaned pgrp fixes
Date: Tue, 4 Mar 2008 18:51:13 +0300	[thread overview]
Message-ID: <20080304155113.GC564@tv-sign.ru> (raw)
In-Reply-To: <20080304122654.7313227010A@magilla.localdomain>

On 03/04, Roland McGrath wrote:
>
> [... big snip...]

Thanks Roland. I need a time to understand your explanation (I even printed
it to read in metro ;). I'll return tomorrow.

A quick note right now:

> static int group_is_really_stopped(struct task_struct *p)
> {
> 	int ret = 0;
> 	spin_lock(&p->sighand->siglock);
> 	ret = (p->signal->flags & (SIGNAL_STOP_STOPPING|SIGNAL_STOP_STOPPED)) ||
> 		p->signal->group_stop_count > 0;
> 	spin_unlock(&p->sighand->siglock);
> 	return ret;
> }

I thought abot something like that too.

However, SIGNAL_STOP_STOPPED doesn't relaible with ptrace. I mean, ptracer
doesn't clear SIGNAL_STOP_STOPPED. This is btw one of the problems which
complicates fixing do_wait(WSTOPPED).

As for SIGNAL_STOP_STOPPING... I am dreaming to find the way to eliminate
this lock-drop in get_signal_to_deliver(). Not sure this is possible, but
it is so nasty. For example, SIGNAL_STOP_DEQUEUED is racy, and I don't know
how to fix this. The patch we discussed some time ago doesn't really work
because dequeue_signal() drops the lock too. The latter is fixable afaics,
but needs very ugly changes.

Oleg.


  reply	other threads:[~2008-03-04 15:47 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-02 18:44 Oleg Nesterov
2008-03-04 12:26 ` Roland McGrath
2008-03-04 15:51   ` Oleg Nesterov [this message]
2008-03-05  1:11     ` Roland McGrath
2008-03-05 16:48       ` Oleg Nesterov
2008-03-05 17:11   ` Oleg Nesterov
2008-03-06  1:14     ` Eric W. Biederman
2008-03-07  1:52       ` Oleg Nesterov
2008-03-07  3:53     ` Roland McGrath

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