From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753994AbXDMOOj (ORCPT ); Fri, 13 Apr 2007 10:14:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754004AbXDMOOj (ORCPT ); Fri, 13 Apr 2007 10:14:39 -0400 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:42272 "EHLO ebiederm.dsl.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753994AbXDMOOi (ORCPT ); Fri, 13 Apr 2007 10:14:38 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Oleg Nesterov Cc: Andrew Morton , Davide Libenzi , Ingo Molnar , Roland McGrath , linux-kernel@vger.kernel.org Subject: Re: [PATCH] change kernel threads to ignore signals instead of blocking them References: <20070413073116.GA1540@tv-sign.ru> Date: Fri, 13 Apr 2007 08:13:32 -0600 In-Reply-To: <20070413073116.GA1540@tv-sign.ru> (Oleg Nesterov's message of "Fri, 13 Apr 2007 11:31:16 +0400") Message-ID: User-Agent: Gnus/5.110006 (No Gnus v0.6) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Oleg Nesterov writes: > On top of Eric's > > kthread-dont-depend-on-work-queues-take-2.patch > > Currently kernel threads use sigprocmask(SIG_BLOCK) to protect against signals. > This doesn't prevent the signal delivery, this only blocks signal_wake_up(). > Every "killall -33 kthreadd" means a "struct siginfo" leak. > > Change kthreadd_setup() to set all handlers to SIG_IGN instead of blocking them > (make a new helper ignore_signals() for that). If the kernel thread needs some > signal, it should use allow_signal() anyway, and in that case it should not use > CLONE_SIGHAND. > > Note that we can't change daemonize() (should die!) in the same way, because > it can be used along with CLONE_SIGHAND. This means that allow_signal() still > should unblock the signal to work correctly with daemonize()ed threads. > > However, disallow_signal() doesn't block the signal any longer but ignores it. > > NOTE: with or without this patch the kernel threads are not protected from > handle_stop_signal(), this seems harmless, but not good. Hmm. I like it all except for disallow_signal. disallow_signal currently only has one user, jffs2. While jffs2 currently doesn't care, given the way jffs2 is using disallow_signal I would expect it would prefer to have the signal blocked. Thinking about this some more if jffs2 or anyone else wants blocked signal behavior they can go ahead and block the signal. Keeping disallow_signal in sync with allow_signal seems to make sense. Nothing in the kernel should break with this change so: Acked-by: "Eric W. Biederman"