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=-5.9 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,URIBL_BLOCKED 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 4CAA0C433E2 for ; Fri, 28 Aug 2020 10:44:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 216DC2098B for ; Fri, 28 Aug 2020 10:44:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598611497; bh=hgX2QECXy5MlJkQZXxuPE3ywxUra609CbNlUd8fZrWM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=agkTKWAbVUKRbTCswGflv0QYxUkOVuNuuFyJVCy7LiUZa3U3VL0tIJVvaF7Sbojym 9+UUl2BEHAk9FriIDhh0Yf4DbpLTO/oHxBl2CbfYOLGDLaHlvng09AioviZ14uRjvE f+zKvopeF/glKZvHytlnXEqdwBaxyAVt/UGoOgzY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728532AbgH1Ko4 (ORCPT ); Fri, 28 Aug 2020 06:44:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:32878 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728362AbgH1Koz (ORCPT ); Fri, 28 Aug 2020 06:44:55 -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 0D2C8208CA; Fri, 28 Aug 2020 10:44:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598611494; bh=hgX2QECXy5MlJkQZXxuPE3ywxUra609CbNlUd8fZrWM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=qIpikyXykAX/Foacgzl2TatAVyOBf2/rpacIrW1noBixkk8bSTQ145gR6NQekKcmq sRVR+WQSjCPRFJvp96+dZtOlXVBHT7ntxUVlYLzgQQCLbhNZUy0HM9qHlWgO4ueKRp 4jyN5L9UeeE26xGexDd/hRKL7EqH9tGHvF5veQrk= Date: Fri, 28 Aug 2020 19:44:49 +0900 From: Masami Hiramatsu To: peterz@infradead.org Cc: linux-kernel@vger.kernel.org, Eddy_Wu@trendmicro.com, x86@kernel.org, davem@davemloft.net, rostedt@goodmis.org, naveen.n.rao@linux.ibm.com, anil.s.keshavamurthy@intel.com, linux-arch@vger.kernel.org, cameron@moodycamel.com, oleg@redhat.com, will@kernel.org, paulmck@kernel.org Subject: Re: [RFC][PATCH 7/7] kprobes: Replace rp->free_instance with freelist Message-Id: <20200828194449.deaae48c36211a61822a1943@kernel.org> In-Reply-To: <20200828091813.GU1362448@hirez.programming.kicks-ass.net> References: <20200827161237.889877377@infradead.org> <20200827161754.594247581@infradead.org> <20200828084851.GQ1362448@hirez.programming.kicks-ass.net> <20200828181341.c1da066360c6085d48850e22@kernel.org> <20200828091813.GU1362448@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-arch-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Fri, 28 Aug 2020 11:18:13 +0200 peterz@infradead.org wrote: > On Fri, Aug 28, 2020 at 06:13:41PM +0900, Masami Hiramatsu wrote: > > On Fri, 28 Aug 2020 10:48:51 +0200 > > peterz@infradead.org wrote: > > > > > On Thu, Aug 27, 2020 at 06:12:44PM +0200, Peter Zijlstra wrote: > > > > struct kretprobe_instance { > > > > union { > > > > + /* > > > > + * Dodgy as heck, this relies on not clobbering freelist::refs. > > > > + * llist: only clobbers freelist::next. > > > > + * rcu: clobbers both, but only after rp::freelist is gone. > > > > + */ > > > > + struct freelist_node freelist; > > > > struct llist_node llist; > > > > - struct hlist_node hlist; > > > > struct rcu_head rcu; > > > > }; > > > > > > Masami, make sure to make this something like: > > > > > > union { > > > struct freelist_node freelist; > > > struct rcu_head rcu; > > > }; > > > struct llist_node llist; > > > > > > for v4, because after some sleep I'm fairly sure what I wrote above was > > > broken. > > > > > > We'll only use RCU once the freelist is gone, so sharing that storage > > > should still be okay. > > > > Hmm, would you mean there is a chance that an instance belongs to > > both freelist and llist? > > So the freelist->refs thing is supposed to pin freelist->next for > concurrent usage, but if we instantly stick it on the > current->kretprobe_instances llist while it's still elevated, we'll > overwrite ->next, which would be bad. OK, I'll pick these up for my v4 series with that fix. Thank you, -- Masami Hiramatsu