From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 725B3C04AAB for ; Tue, 7 May 2019 08:58:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44AD9204FD for ; Tue, 7 May 2019 08:58:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726921AbfEGI64 (ORCPT ); Tue, 7 May 2019 04:58:56 -0400 Received: from mx2.suse.de ([195.135.220.15]:44488 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726331AbfEGI6z (ORCPT ); Tue, 7 May 2019 04:58:55 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 77065ABAC; Tue, 7 May 2019 08:58:54 +0000 (UTC) Date: Tue, 7 May 2019 10:58:53 +0200 (CEST) From: Miroslav Benes To: Josh Poimboeuf cc: Petr Mladek , Jiri Kosina , Joe Lawrence , Kamalesh Babulal , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] livepatch: Remove duplicate warning about missing reliable stacktrace support In-Reply-To: <20190507004032.2fgddlsycyypqdsn@treble> Message-ID: References: <20190430091049.30413-1-pmladek@suse.com> <20190430091049.30413-2-pmladek@suse.com> <20190507004032.2fgddlsycyypqdsn@treble> User-Agent: Alpine 2.21 (LSU 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 6 May 2019, Josh Poimboeuf wrote: > On Tue, Apr 30, 2019 at 11:10:48AM +0200, Petr Mladek wrote: > > WARN_ON_ONCE() could not be called safely under rq lock because > > of console deadlock issues. Fortunately, there is another check > > for the reliable stacktrace support in klp_enable_patch(). > > > > Signed-off-by: Petr Mladek > > --- > > kernel/livepatch/transition.c | 9 ++++++++- > > 1 file changed, 8 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c > > index 9c89ae8b337a..8e0274075e75 100644 > > --- a/kernel/livepatch/transition.c > > +++ b/kernel/livepatch/transition.c > > @@ -263,8 +263,15 @@ static int klp_check_stack(struct task_struct *task, char *err_buf) > > trace.nr_entries = 0; > > trace.max_entries = MAX_STACK_ENTRIES; > > trace.entries = entries; > > + > > ret = save_stack_trace_tsk_reliable(task, &trace); > > - WARN_ON_ONCE(ret == -ENOSYS); > > + /* > > + * pr_warn() under task rq lock might cause a deadlock. > > + * Fortunately, missing reliable stacktrace support has > > + * already been handled when the livepatch was enabled. > > + */ > > + if (ret == -ENOSYS) > > + return ret; > > I find the comment to be a bit wordy and confusing (and vague). > > Also this check is effectively the same as the klp_have_reliable_stack() > check which is done in kernel/livepatch/core.c. So I think it would be > clearer and more consistent if the same check is done here: > > if (!klp_have_reliable_stack()) > return -ENOSYS; We removed it in 1d98a69e5cef ("livepatch: Remove reliable stacktrace check in klp_try_switch_task()") and I do think it does not belong here. We can check for the facility right at the beginning in klp_enable_patch() and it is not necessary to do it every time klp_check_stack() is called. But it is nothing I could not live with, so if you decide it is better, I will not object. Miroslav