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 7A7A5C46471 for ; Tue, 7 Aug 2018 11:36:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B105214DA for ; Tue, 7 Aug 2018 11:36:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B105214DA 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 S2387942AbeHGNuX (ORCPT ); Tue, 7 Aug 2018 09:50:23 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:41946 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726555AbeHGNuX (ORCPT ); Tue, 7 Aug 2018 09:50:23 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B59F540241C4; Tue, 7 Aug 2018 11:36:27 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.34.27.30]) by smtp.corp.redhat.com (Postfix) with SMTP id B15801C663; Tue, 7 Aug 2018 11:36:23 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 7 Aug 2018 13:36:27 +0200 (CEST) Date: Tue, 7 Aug 2018 13:36:23 +0200 From: Oleg Nesterov To: Ravi Bangoria Cc: srikar@linux.vnet.ibm.com, 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 v7 3/6] Uprobes: Support SDT markers having reference count (semaphore) Message-ID: <20180807113622.GC19831@redhat.com> References: <20180731035143.11942-1-ravi.bangoria@linux.ibm.com> <20180731035143.11942-4-ravi.bangoria@linux.ibm.com> <20180803112455.GA13794@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.7]); Tue, 07 Aug 2018 11:36:27 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.7]); Tue, 07 Aug 2018 11:36:27 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.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 Hi Ravi, On 08/06, Ravi Bangoria 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; > > > > I am surprised I didn't notice this before... > > > > So > > du->mm = mm; > > > > is fine, mm can't go away, uprobe_clear_state() does delayed_uprobe_remove(NULL,mm). > > > > But > > du->uprobe = uprobe; > > > > doesn't look right, uprobe can go away and it can be freed, its memory can be reused. > > We can't rely on remove_breakpoint(), > > > I'm sorry. I didn't get this. How can uprobe go away without calling > uprobe_unregister() > -> rergister_for_each_vma() > -> remove_breakpoint() > And remove_breakpoint() will get called assuming that _unregister() will find the same vma with the probed insn. But as I said, the application can munmap the probed page/vma. No? > > Also. delayed_uprobe_add() should check the list and avoid duplicates. Otherwise the > > trivial > > > > for (;;) > > munmap(mmap(uprobed_file)); > > > > will eat the memory until uprobe is unregistered. > > > I'm already calling delayed_uprobe_check(uprobe, mm) from delayed_uprobe_add(). Oops ;) Oleg.