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=-6.8 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 11065C433DF for ; Thu, 27 Aug 2020 18:01:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DCC1322B4B for ; Thu, 27 Aug 2020 18:01:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598551268; bh=Bn0qulrmGo8+JQLEGDP+lfcoVCxev5sxmZ5f0aMh91E=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=BbXqveHPqtD3t+agJc9smEDh2quW/emi3jR7lOc8ObpklSLei0h40Vq+7d5eRSIb5 36nIQhOX7LRTrKbfVHcByWUWo+nZnmFvszJYY4V7LyMJrgqVPxPCIAiB/Kk8pQIt/F wd7tgo3UjmbcjqzehY4RFWbNNy8Qnh9EJ8HUwAzE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726197AbgH0SBI (ORCPT ); Thu, 27 Aug 2020 14:01:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:43302 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726120AbgH0SBG (ORCPT ); Thu, 27 Aug 2020 14:01:06 -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 5677620707; Thu, 27 Aug 2020 18:01:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598551265; bh=Bn0qulrmGo8+JQLEGDP+lfcoVCxev5sxmZ5f0aMh91E=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Bv5KwTQrNOQsC28a1+5pESc4J4vEuC/qxLUTPtaLYWoTnRxleN4e7QgV+ZwRzliAs kk7jRqkpW6c1qsrDoKgvcRk12aMZhHDobDmwfRuVvVJCCa9lU+1MMgpYMTYsk7kRAa qBg31/RgmB9isZHCArBsPWeIHfNVVCnoM/ksnvgc= Date: Fri, 28 Aug 2020 03:00:59 +0900 From: Masami Hiramatsu To: Peter Zijlstra 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 3/7] kprobes: Remove kretprobe hash Message-Id: <20200828030059.d6618caf5b0214c424b941df@kernel.org> In-Reply-To: <20200827161754.359432340@infradead.org> References: <20200827161237.889877377@infradead.org> <20200827161754.359432340@infradead.org> 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 Thu, 27 Aug 2020 18:12:40 +0200 Peter Zijlstra wrote: > +static void invalidate_rp_inst(struct task_struct *t, struct kretprobe *rp) > +{ > + struct invl_rp_ipi iri = { > + .task = t, > + .rp = rp, > + .done = false > + }; > + > + for (;;) { > + if (try_invoke_on_locked_down_task(t, __invalidate_rp_inst, rp)) > + return; > + > + smp_call_function_single(task_cpu(t), __invalidate_rp_ipi, &iri, 1); > + if (iri.done) > + return; > + } Hmm, what about making a status place holder and point it from each instance to tell it is valid or not? struct kretprobe_holder { atomic_t refcnt; struct kretprobe *rp; }; struct kretprobe { ... struct kretprobe_holder *rph; // allocate at register ... }; struct kretprobe_instance { ... struct kretprobe_holder *rph; // free if refcnt == 0 ... }; cleanup_rp_inst(struct kretprobe *rp) { rp->rph->rp = NULL; } kretprobe_trampoline_handler() { ... rp = READ_ONCE(ri->rph-rp); if (likely(rp)) { // call rp->handler } else rcu_call(ri, free_rp_inst_rcu); ... } free_rp_inst_rcu() { if (!atomic_dec_return(ri->rph->refcnt)) kfree(ri->rph); kfree(ri); } This increase kretprobe_instance a bit, but make things simpler. (and still keep lockless, atomic op is in the rcu callback). Thank you, -- Masami Hiramatsu