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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 66F07C433E0 for ; Wed, 27 Jan 2021 03:33:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 39E3E205CA for ; Wed, 27 Jan 2021 03:33:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236200AbhA0Dcs (ORCPT ); Tue, 26 Jan 2021 22:32:48 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:27937 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729485AbhAZVS6 (ORCPT ); Tue, 26 Jan 2021 16:18:58 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1611695852; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ZegfSQaVgR/gl1215NTcom+C+m68vfkGvT34DFtcorI=; b=QHH1WrnE9RnnhCl/Jq1WsxHnH2yBTMk2QLgyYwYURdgZx/SMr53z01BXNi/Safmm3eKLwa wtgTVO7FCuCbDcTdft503pzTwQHVed0QohvyeTQdNw2SAkjkiywcWVbLvGl/YcSWpNycbJ EJmBPcIuIWKSuaY166beL7tXy1Cj9Io= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-146-sKZ4waErPguMXlXgrqyjPA-1; Tue, 26 Jan 2021 16:17:27 -0500 X-MC-Unique: sKZ4waErPguMXlXgrqyjPA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 117A8A0C23; Tue, 26 Jan 2021 21:17:26 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.29]) by smtp.corp.redhat.com (Postfix) with SMTP id 9E4551F0; Tue, 26 Jan 2021 21:17:24 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 26 Jan 2021 22:17:25 +0100 (CET) Date: Tue, 26 Jan 2021 22:17:23 +0100 From: Oleg Nesterov To: Steven Rostedt Cc: Masami Hiramatsu , Jianlin Lv , mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] tracing: precise log info for kretprobe addr err Message-ID: <20210126211722.GA23645@redhat.com> References: <20210125160108.2147511-1-Jianlin.Lv@arm.com> <20210125181926.GA10248@redhat.com> <20210125133840.511b1496@gandalf.local.home> <20210126131536.f6e3a737a7b948799084fa7a@kernel.org> <20210126202058.GC12469@redhat.com> <20210126154302.302a3bb0@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210126154302.302a3bb0@gandalf.local.home> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/26, Steven Rostedt wrote: > > On Tue, 26 Jan 2021 21:20:59 +0100 > Oleg Nesterov wrote: > > > > No, not wrong. Even offset != 0, if the symbol exists in the kernel, > > > kprobe_on_func_entry() will check it. > > > > Yes, but unless I am totally confused... if kprobe_on_func_entry() returns false, > > then trace_kprobe_create() should fail with BAD_RETPROBE even if offset == 0 ? > > From what I understand. kprobe_on_func_entry() can return false if you pass > in: "MOD:not_yet_loaded_module_func", but this is OK, because when the > module is loaded, and the "not_yet_loaded_module_func" exists, the > kretprobe will then be added. > > The strchr(symbol,":") check is to see if "MOD:" (or some other ":" command) > is in the name, and we don't want it to fail if it is. Which is why we > should have that commented. Agreed, this matches my understanding. But just in case... not sure I read this code correctly, but I think that module_kallsyms_lookup_name("not_yet_loaded_module_func") should work even without the "MOD:" prefix. IOW, kprobe_on_func_entry("not_yet_loaded_module_func") can fail, and then later succeed if you load the module which provides this symbol. But even if I am right, I agree with the strchr(symbol,":") check. Oleg.