linux-kernel - Re: [PATCH] signals: do_tkill: don't use tasklist

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Date:	Fri, 7 Mar 2008 23:23:16 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Roland McGrath <roland@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] signals: do_tkill: don't use tasklist_lock

On 03/07, Oleg Nesterov wrote:
>
> Suppose that the main thread is already dead (dequeued SIGKILL), but
> not yet released. This window is not that small. In that window (before
> de_thread() switches pids) any private signal (even SIGKILL) sent to the
> main thread will be silently lost.
> 
> To do a proper fix, we should change de_thread() so that the new leader
> also "inherits" old_leader->pending signals.

Ah, even this is not enough if we want a "perfect" fix. Because the private
SIGKILL will be "ignored" until the main thread dequeues the SIGKILL which
was sent by de_thread().

We can change __group_complete_signal/zap_other_threads so that they won't
do sigaddset(), just signal_wake_up(). But in that case dequeue_signal()
and recalc_signal() should take signal_group_exit into account...

Oleg.

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