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=-6.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,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 378A3C432C3 for ; Thu, 14 Nov 2019 19:47:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 172D620729 for ; Thu, 14 Nov 2019 19:47:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726977AbfKNTrn (ORCPT ); Thu, 14 Nov 2019 14:47:43 -0500 Received: from mail.kernel.org ([198.145.29.99]:32902 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726098AbfKNTrl (ORCPT ); Thu, 14 Nov 2019 14:47:41 -0500 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8A7A620723; Thu, 14 Nov 2019 19:47:40 +0000 (UTC) Received: from rostedt by gandalf.local.home with local (Exim 4.92.2) (envelope-from ) id 1iVL5f-0001wG-1z; Thu, 14 Nov 2019 14:47:39 -0500 Message-Id: <20191114194738.938540273@goodmis.org> User-Agent: quilt/0.65 Date: Thu, 14 Nov 2019 14:46:37 -0500 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Alexei Starovoitov Subject: [RFC][PATCH 1/2] ftrace: Add modify_ftrace_direct() References: <20191114194636.811109457@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Steven Rostedt (VMware)" Add a new function modify_ftrace_direct() that will allow a user to update an existing direct caller to a new trampoline, without missing hits due to unregistering one and then adding another. Link: https://lore.kernel.org/r/20191109022907.6zzo6orhxpt5n2sv@ast-mbp.dhcp.thefacebook.com Suggested-by: Alexei Starovoitov Signed-off-by: Steven Rostedt (VMware) --- include/linux/ftrace.h | 6 ++++ kernel/trace/ftrace.c | 78 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 84 insertions(+) diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h index 55647e185141..73eb2e93593f 100644 --- a/include/linux/ftrace.h +++ b/include/linux/ftrace.h @@ -250,6 +250,7 @@ static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { extern int ftrace_direct_func_count; int register_ftrace_direct(unsigned long ip, unsigned long addr); int unregister_ftrace_direct(unsigned long ip, unsigned long addr); +int modify_ftrace_direct(unsigned long ip, unsigned long old_addr, unsigned long new_addr); struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr); #else # define ftrace_direct_func_count 0 @@ -261,6 +262,11 @@ static inline int unregister_ftrace_direct(unsigned long ip, unsigned long addr) { return -ENODEV; } +static inline int modify_ftrace_direct(unsigned long ip, + unsigned long old_addr, unsigned long new_addr) +{ + return -ENODEV; +} static inline struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr) { return NULL; diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 82ef8d60a42b..834f3556ea1e 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5160,6 +5160,84 @@ int unregister_ftrace_direct(unsigned long ip, unsigned long addr) return ret; } EXPORT_SYMBOL_GPL(unregister_ftrace_direct); + +static struct ftrace_ops stub_ops = { + .func = ftrace_stub, +}; + +/** + * modify_ftrace_direct - Modify an existing direct call to call something else + * @ip: The instruction pointer to modify + * @old_addr: The address that the current @ip calls directly + * @new_addr: The address that the @ip should call + * + * This modifies a ftrace direct caller at an instruction pointer without + * having to disable it first. The direct call will switch over to the + * @new_addr without missing anything. + * + * Returns: zero on success. Non zero on error, which includes: + * -ENODEV : the @ip given has no direct caller attached + * -EINVAL : the @old_addr does not match the current direct caller + */ +int modify_ftrace_direct(unsigned long ip, + unsigned long old_addr, unsigned long new_addr) +{ + struct ftrace_func_entry *entry; + struct dyn_ftrace *rec; + int ret = -ENODEV; + + mutex_lock(&direct_mutex); + entry = __ftrace_lookup_ip(direct_functions, ip); + if (!entry) { + /* OK if it is off by a little */ + rec = lookup_rec(ip, ip); + if (!rec || rec->ip == ip) + goto out_unlock; + + entry = __ftrace_lookup_ip(direct_functions, rec->ip); + if (!entry) + goto out_unlock; + + ip = rec->ip; + WARN_ON(!(rec->flags & FTRACE_FL_DIRECT)); + } + + ret = -EINVAL; + if (entry->direct != old_addr) + goto out_unlock; + + /* + * By setting a stub function at the same address, we force + * the code to call the iterator and the direct_ops helper. + * This means that @ip does not call the direct call, and + * we can simply modify it. + */ + ret = ftrace_set_filter_ip(&stub_ops, ip, 0, 0); + if (ret) + goto out_unlock; + + ret = register_ftrace_function(&stub_ops); + if (ret) { + ftrace_set_filter_ip(&stub_ops, ip, 1, 0); + goto out_unlock; + } + + entry->direct = new_addr; + + /* + * By removing the stub, we put back the direct call, calling + * the @new_addr. + */ + unregister_ftrace_function(&stub_ops); + ftrace_set_filter_ip(&stub_ops, ip, 1, 0); + + ret = 0; + + out_unlock: + mutex_unlock(&direct_mutex); + return ret; +} +EXPORT_SYMBOL_GPL(modify_ftrace_direct); #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */ /** -- 2.23.0