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=-8.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_NEOMUTT 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 C115EC04A6B for ; Tue, 7 May 2019 00:40:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8C0B920856 for ; Tue, 7 May 2019 00:40:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726527AbfEGAkj (ORCPT ); Mon, 6 May 2019 20:40:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48104 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726073AbfEGAkj (ORCPT ); Mon, 6 May 2019 20:40:39 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id F02F859468; Tue, 7 May 2019 00:40:38 +0000 (UTC) Received: from treble (ovpn-123-166.rdu2.redhat.com [10.10.123.166]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 403B1611CF; Tue, 7 May 2019 00:40:34 +0000 (UTC) Date: Mon, 6 May 2019 19:40:32 -0500 From: Josh Poimboeuf To: Petr Mladek Cc: Jiri Kosina , Miroslav Benes , 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 Message-ID: <20190507004032.2fgddlsycyypqdsn@treble> References: <20190430091049.30413-1-pmladek@suse.com> <20190430091049.30413-2-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190430091049.30413-2-pmladek@suse.com> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Tue, 07 May 2019 00:40:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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; ret = save_stack_trace_tsk_reliable(task, &trace); [ no need to check ret for ENOSYS here ] Then, IMO, no comment is needed. -- Josh