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=-7.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS 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 A9C6FC433DF for ; Wed, 26 Aug 2020 08:32:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6844F207BC for ; Wed, 26 Aug 2020 08:32:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598430724; bh=+zgvqau40KD6zoirbrmJVE9a/bFPfvd4D/v0f4gdpg0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=QWkgdHZ8xJcVJjGZYGjnfyFxo+jmjVIcqTny3D0mVxg3R5T38w9genj9BPeF3JXRR vmf8mJydFlMSzqmF3pbZN+rhDyMAvQImNfVf92scZ+VQbMNdFrUkUI+fBFvIRVDneM xBP5LuIM75pdVDKwR3fhLnSx1Ouvuyr7Xqah7WNg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727020AbgHZIcD (ORCPT ); Wed, 26 Aug 2020 04:32:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:49634 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726884AbgHZIcC (ORCPT ); Wed, 26 Aug 2020 04:32:02 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 6328F20707; Wed, 26 Aug 2020 08:32:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598430722; bh=+zgvqau40KD6zoirbrmJVE9a/bFPfvd4D/v0f4gdpg0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=eHNvNWFO+gU8BFaCL0EtG2rT/AVfXwkqWtRtCRSY59S9Sz/5O1xW+6E138Fj1pyOa F8gswCtGY64ln7vX1d1Q9rUXCdgacbqatvlhfTfqJmwxLEhyrlOLNXLR5EeoXXDps3 jfUAbaiG0OQXxHBXg1qXgy3Tn1g+CFIff66n92Mg= Date: Wed, 26 Aug 2020 17:31:58 +0900 From: Masami Hiramatsu To: peterz@infradead.org Cc: "Eddy_Wu@trendmicro.com" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "David S. Miller" Subject: Re: x86/kprobes: kretprobe fails to triggered if kprobe at function entry is not optimized (trigger by int3 breakpoint) Message-Id: <20200826173158.19bc6f5c3b05fbb3f6d0aa3e@kernel.org> In-Reply-To: <20200825120911.GX1362448@hirez.programming.kicks-ass.net> References: <8816bdbbc55c4d2397e0b02aad2825d3@trendmicro.com> <20200825005426.f592075d13be740cb3c9aa77@kernel.org> <7396e7b2079644a6aafd9670a111232b@trendmicro.com> <20200825151538.f856d701a34f4e0561a64932@kernel.org> <20200825120911.GX1362448@hirez.programming.kicks-ass.net> X-Mailer: Sylpheed 3.7.0 (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 Hi Peter, On Tue, 25 Aug 2020 14:09:11 +0200 peterz@infradead.org wrote: > > @@ -1934,50 +1884,28 @@ unsigned long __weak arch_deref_entry_point(void *entry) > static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs) > { > struct kretprobe *rp = container_of(p, struct kretprobe, kp); > - unsigned long hash, flags = 0; > struct kretprobe_instance *ri; > + struct llist_node *llist; > > - /* > - * To avoid deadlocks, prohibit return probing in NMI contexts, > - * just skip the probe and increase the (inexact) 'nmissed' > - * statistical counter, so that the user is informed that > - * something happened: > - */ > - if (unlikely(in_nmi())) { > + llist = llist_del_first(&rp->free_instances); > + if (!llist) { > rp->nmissed++; > return 0; > } Would we need a lock around llist_del_first(&rp->free_instance) here? linux/llist.h said, * Cases where locking is not needed: * If there are multiple producers and multiple consumers, llist_add can be * used in producers and llist_del_all can be used in consumers simultaneously * without locking. Also a single consumer can use llist_del_first while ^^^^^^^^^^^^^^^^^^^^^^^ * multiple producers simultaneously use llist_add, without any locking. * * Cases where locking is needed: * If we have multiple consumers with llist_del_first used in one consumer, and ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ * llist_del_first or llist_del_all used in other consumers, then a lock is * needed. pre_handler_kretprobe() can be invoked simultaneously on the different CPUs if those are calling the same probed function. Thank you, -- Masami Hiramatsu