Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761325Ab2BNWuY (ORCPT ); Tue, 14 Feb 2012 17:50:24 -0500 Received: from mail-bk0-f46.google.com ([209.85.214.46]:34256 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761289Ab2BNWuW (ORCPT ); Tue, 14 Feb 2012 17:50:22 -0500 Date: Wed, 15 Feb 2012 02:50:17 +0400 From: Anton Vorontsov To: Oleg Nesterov , Andrew Morton , Greg Kroah-Hartman Cc: rientjes@google.com, linux-kernel@vger.kernel.org Subject: [PATCH] sysrq: Use SEND_SIG_FORCED instead of force_sig() Message-ID: <20120214225017.GA12360@oksana.dev.rtsoft.ru> References: <13288070803232@kroah.org> <20120210201008.GA21009@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20120210201008.GA21009@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2580 Lines: 84 Change send_sig_all() to use do_send_sig_info(SEND_SIG_FORCED) instead of force_sig(SIGKILL). With the recent changes we do not need force_ to kill the CLONE_NEWPID tasks. And this is more correct. force_sig() can race with the exiting thread, while do_send_sig_info(group => true) kill the whole process. Suggested-by: Oleg Nesterov Signed-off-by: Anton Vorontsov --- On Fri, Feb 10, 2012 at 09:10:08PM +0100, Oleg Nesterov wrote: > > --- a/drivers/tty/sysrq.c > > +++ b/drivers/tty/sysrq.c > > @@ -324,9 +324,12 @@ static void send_sig_all(int sig) > > > > read_lock(&tasklist_lock); > > for_each_process(p) { > > - if (p->mm && !is_global_init(p)) > > - /* Not swapper, init nor kernel thread */ > > - force_sig(sig, p); > > + if (p->flags & PF_KTHREAD) > > + continue; > > + if (is_global_init(p)) > > + continue; > > + > > + force_sig(sig, p); > > } > > read_unlock(&tasklist_lock); > > Obviously I agree with this change. > > But where does this read_lock(tasklist) come from? It came from this patch: http://lkml.org/lkml/2012/2/7/24 > We discussed this with Anton. Yes, tasklist ensures that > force_sig() can't crash the kernel. But it is still wrong > and should not be used. > > I think send_sig_all() should use SEND_SIG_FORCED (this > depends on the patches I sent to Andrew), in this case > tasklist is not needed. Well, I think the lock is still a good thing: we don't want any new processes to be created while we kill others. I might be wrong, but copy_process() issues recalc_sigpending() under tasklist lock especially the for this scenario. So, in this and in OOM cases we have to be precise (unlike LMK). Sysrq is a rare thing, so there is actually should be no problem with holding the lock. So, how about this patch? Greg, can we take it via -mm tree, as it depends on a few sched patches? drivers/tty/sysrq.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 8db9125..5ab8039 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -329,7 +329,7 @@ static void send_sig_all(int sig) if (is_global_init(p)) continue; - force_sig(sig, p); + do_send_sig_info(sig, SEND_SIG_FORCED, p, true); } read_unlock(&tasklist_lock); } -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/