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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 E088EC04AB6 for ; Fri, 31 May 2019 13:29:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BF5AB2696E for ; Fri, 31 May 2019 13:29:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726687AbfEaN3o (ORCPT ); Fri, 31 May 2019 09:29:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:48508 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726418AbfEaN3o (ORCPT ); Fri, 31 May 2019 09:29:44 -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 F3D19AE4E; Fri, 31 May 2019 13:29:42 +0000 (UTC) Date: Fri, 31 May 2019 15:29:42 +0200 (CEST) From: Miroslav Benes To: Petr Mladek cc: Jiri Kosina , Josh Poimboeuf , Joe Lawrence , Kamalesh Babulal , live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] livepatch: Remove duplicate warning about missing reliable stacktrace support In-Reply-To: <20190531131906.lkhrfgpze57pqrcg@pathway.suse.cz> Message-ID: References: <20190531074147.27616-1-pmladek@suse.com> <20190531074147.27616-3-pmladek@suse.com> <20190531131906.lkhrfgpze57pqrcg@pathway.suse.cz> 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 Fri, 31 May 2019, Petr Mladek wrote: > On Fri 2019-05-31 14:32:34, Miroslav Benes wrote: > > On Fri, 31 May 2019, Petr Mladek wrote: > > > > > WARN_ON_ONCE() could not be called safely under rq lock because > > > of console deadlock issues. > > > > > > It can be simply removed. A better descriptive message is written > > > in klp_enable_patch() when klp_have_reliable_stack() fails. > > > The remaining debug message is good enough. > > > > > > Signed-off-by: Petr Mladek > > > --- > > > kernel/livepatch/transition.c | 1 - > > > 1 file changed, 1 deletion(-) > > > > > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c > > > index abb2a4a2cbb2..1bf362df76e1 100644 > > > --- a/kernel/livepatch/transition.c > > > +++ b/kernel/livepatch/transition.c > > > @@ -247,7 +247,6 @@ static int klp_check_stack(struct task_struct *task, char *err_buf) > > > int ret, nr_entries; > > > > > > ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries)); > > > - WARN_ON_ONCE(ret == -ENOSYS); > > > if (ret < 0) { > > > snprintf(err_buf, STACK_ERR_BUF_SIZE, > > > "%s: %s:%d has an unreliable stack\n", > > > > The current situation is not the best, but I think the patch improves it > > only slightly. I see two possible solutions. > > > > 1. we either revert commit 1d98a69e5cef ("livepatch: Remove reliable > > stacktrace check in klp_try_switch_task()"), so that klp_check_stack() > > returns right away. > > > > 2. or we test ret from stack_trace_save_tsk_reliable() for ENOSYS and > > return. > > > > In my opinion either of them is better than what we have now (and what we > > would have with the patch), because klp_check_stack() returns, but it > > prints out that a task has an unreliable stack. Yes, it is pr_debug() only > > in the end, but still. > > IMHO, any extra check will not improve the situation much. Quiet > return is as useless as the misleading pr_debug() that will > not normally get printed anyway. I disagree here. I think the silent return would be perfectly fine. The user was warned in klp_enable_patch() already. Miroslav