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_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 B6FAFC004C9 for ; Sun, 5 May 2019 19:34:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8467C208C0 for ; Sun, 5 May 2019 19:34:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727919AbfEETeu (ORCPT ); Sun, 5 May 2019 15:34:50 -0400 Received: from mail.kernel.org ([198.145.29.99]:40604 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727343AbfEETeu (ORCPT ); Sun, 5 May 2019 15:34:50 -0400 Received: from oasis.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 C70552087F; Sun, 5 May 2019 19:34:48 +0000 (UTC) Date: Sun, 5 May 2019 15:34:47 -0400 From: Steven Rostedt To: Cheng Jian Cc: , , , Subject: Re: [PATCH] ftrace: enable trampoline when rec count decrement to one Message-ID: <20190505153447.594d4eab@oasis.local.home> In-Reply-To: <1556969979-111047-1-git-send-email-cj.chengjian@huawei.com> References: <1556969979-111047-1-git-send-email-cj.chengjian@huawei.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 4 May 2019 19:39:39 +0800 Cheng Jian wrote: > Trampoline can only be enabled if there is only a single ops > attached to it. If there's only a single callback registered > to a function, and the ops has a trampoline registered for it, > then we can call the trampoline directly. This is very useful > for improving the performance of ftrace and livepatch. > > But we always disable trampoline when unregister ftrace. So if > you have registered multiple ftrace_ops at the same location, > even if the other ones have been unregistered, you will no longer > be able to use trampoline. > > To fix it, set FTRACE_FL_TRAMP flag if rec count is decremented > to one, and the ops that left has a trampoline. > > Testing After this patch : > > insmod livepatch_unshare_files.ko > cat /sys/kernel/debug/tracing/enabled_functions > > unshare_files (1) R I tramp: 0xffffffffc0000000(klp_ftrace_handler+0x0/0xa0) ->ftrace_ops_assist_func+0x0/0xf0 > > echo unshare_files > /sys/kernel/debug/tracing/set_ftrace_filter > echo function > /sys/kernel/debug/tracing/current_tracer > cat /sys/kernel/debug/tracing/enabled_functions > > unshare_files (2) R I ->ftrace_ops_list_func+0x0/0x150 > > echo nop > /sys/kernel/debug/tracing/current_tracer > cat /sys/kernel/debug/tracing/enabled_functions > > unshare_files (1) R I tramp: 0xffffffffc0000000(klp_ftrace_handler+0x0/0xa0) ->ftrace_ops_assist_func+0x0/0xf0 Thanks for the patch. There was some race condition that prevented me from doing this in the first place, but unfortunately, I don't remember what that was :-/ I'll have to think about this before applying this patch. Maybe there isn't a race condition, and I was just playing it safe, as there was a race condition between switching from regs caller back to non regs caller. -- Steve > > Signed-off-by: Cheng Jian > --- > kernel/trace/ftrace.c | 28 +++++++++++++++------------- > 1 file changed, 15 insertions(+), 13 deletions(-) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index b920358..bdc29c2 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -1626,6 +1626,11 @@ static bool test_rec_ops_needs_regs(struct > dyn_ftrace *rec) return keep_regs; > } > > +static struct ftrace_ops * > +ftrace_find_tramp_ops_any(struct dyn_ftrace *rec); > +static struct ftrace_ops * > +ftrace_find_tramp_ops_next(struct dyn_ftrace *rec, struct ftrace_ops > *ops); + > static bool __ftrace_hash_rec_update(struct ftrace_ops *ops, > int filter_hash, > bool inc) > @@ -1754,15 +1759,17 @@ static bool __ftrace_hash_rec_update(struct > ftrace_ops *ops, } > > /* > - * If the rec had TRAMP enabled, then it > needs to > - * be cleared. As TRAMP can only be enabled > iff > - * there is only a single ops attached to it. > - * In otherwords, always disable it on > decrementing. > - * In the future, we may set it if rec count > is > - * decremented to one, and the ops that is > left > - * has a trampoline. > + * The TRAMP needs to be set only if rec > count > + * is decremented to one, and the ops that is > + * left has a trampoline. As TRAMP can only > be > + * enabled if there is only a single ops > attached > + * to it. > */ > - rec->flags &= ~FTRACE_FL_TRAMP; > + if (ftrace_rec_count(rec) == 1 && > + ftrace_find_tramp_ops_any(rec)) > + rec->flags |= FTRACE_FL_TRAMP; > + else > + rec->flags &= ~FTRACE_FL_TRAMP; > > /* > * flags will be cleared in > ftrace_check_record() @@ -1955,11 +1962,6 @@ static void > print_ip_ins(const char *fmt, const unsigned char *p) > printk(KERN_CONT "%s%02x", i ? ":" : "", p[i]); } > > -static struct ftrace_ops * > -ftrace_find_tramp_ops_any(struct dyn_ftrace *rec); > -static struct ftrace_ops * > -ftrace_find_tramp_ops_next(struct dyn_ftrace *rec, struct ftrace_ops > *ops); - > enum ftrace_bug_type ftrace_bug_type; > const void *ftrace_expected; >