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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 E1A5DC46464 for ; Mon, 13 Aug 2018 11:23:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A2BD8208A1 for ; Mon, 13 Aug 2018 11:23:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A2BD8208A1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729756AbeHMOFU (ORCPT ); Mon, 13 Aug 2018 10:05:20 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:33678 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728493AbeHMOFU (ORCPT ); Mon, 13 Aug 2018 10:05:20 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 50F3F818F02C; Mon, 13 Aug 2018 11:23:29 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id F06661006EAD; Mon, 13 Aug 2018 11:23:25 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 13 Aug 2018 13:23:29 +0200 (CEST) Date: Mon, 13 Aug 2018 13:23:25 +0200 From: Oleg Nesterov To: Srikar Dronamraju Cc: Ravi Bangoria , rostedt@goodmis.org, mhiramat@kernel.org, liu.song.a23@gmail.com, peterz@infradead.org, mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, linux-kernel@vger.kernel.org, ananth@linux.vnet.ibm.com, alexis.berlemont@gmail.com, naveen.n.rao@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org, linux-mips@linux-mips.org, linux@armlinux.org.uk, ralf@linux-mips.org, paul.burton@mips.com Subject: Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore) Message-ID: <20180813112324.GA28360@redhat.com> References: <20180809041856.1547-1-ravi.bangoria@linux.ibm.com> <20180809041856.1547-4-ravi.bangoria@linux.ibm.com> <20180813100327.GF44470@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180813100327.GF44470@linux.vnet.ibm.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Mon, 13 Aug 2018 11:23:29 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Mon, 13 Aug 2018 11:23:29 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'oleg@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/13, Srikar Dronamraju wrote: > > > + > > +static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm) > > +{ > > + struct delayed_uprobe *du; > > + > > + if (delayed_uprobe_check(uprobe, mm)) > > + return 0; > > + > > + du = kzalloc(sizeof(*du), GFP_KERNEL); > > + if (!du) > > + return -ENOMEM; > > + > > + du->uprobe = uprobe; > > + du->mm = mm; > > + list_add(&du->list, &delayed_uprobe_list); > > + return 0; > > +} > > + > > Should we keep the delayed uprobe list per mm? > That way we could avoid the global mutex lock. > And the list to traverse would also be small. Plus uprobe_mmap() could simply check list_empty(mm->delayed_list) before the costly delayed_uprobe_install(). Yes, I mentioned this too. But then I suggested to not do this in the initial version to make it more simple. Hopefully we can do this later, but note that this conflicts with the change in put_uprobe() you commented below. > > static void put_uprobe(struct uprobe *uprobe) > > { > > - if (atomic_dec_and_test(&uprobe->ref)) > > + if (atomic_dec_and_test(&uprobe->ref)) { > > + /* > > + * If application munmap(exec_vma) before uprobe_unregister() > > + * gets called, we don't get a chance to remove uprobe from > > + * delayed_uprobe_list in remove_breakpoint(). Do it here. > > + */ > > + delayed_uprobe_remove(uprobe, NULL); > > I am not getting this part. If unmap happens before unregister, > why cant we use uprobe_munmap? How? I mean what exactly can we do in uprobe_munmap() ? Firstly, we will need to restore build_probe_list/list_for_each_entry_safe(pending_list) in uprobe_munmap() and this is not nice performance-wise. Then what? We don't even know if the caller is actually munmap(), it can be vma_adjust() and in the latter case we can't do delayed_uprobe_remove(uprobe, mm). Perhaps we can use uprobe_munmap() to cleanup the delayed_uprobe_list, but this doesn't look simple to me. In fact I think that we should simply kill uprobe_munmap(). Oleg.