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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS 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 8131FC46464 for ; Tue, 14 Aug 2018 16:35:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 35F802172B for ; Tue, 14 Aug 2018 16:35:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="JsYr5nvj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 35F802172B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.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 S1732832AbeHNTX3 (ORCPT ); Tue, 14 Aug 2018 15:23:29 -0400 Received: from mail-qk0-f194.google.com ([209.85.220.194]:39419 "EHLO mail-qk0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732191AbeHNTX3 (ORCPT ); Tue, 14 Aug 2018 15:23:29 -0400 Received: by mail-qk0-f194.google.com with SMTP id b5-v6so13812438qkg.6 for ; Tue, 14 Aug 2018 09:35:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=Pqmj3ClLJHm0NWuPcuK5T5mzzNcGqtnI3cr79Wbf/BE=; b=JsYr5nvjfZGsIkd4j3LjWGsU0CZexJlXnv+bhDZIWUoOZrcD0Jz3tRhkjZQG2+RCfy P1wGl7Xt4rD9FeR34KfEDqtvmauOUarEzdONy+ZMuel2gwAXO9nsdSfZVCOkFEZ3JQ/w yQtv3XqObH/MYh44UKcN7yZCFv4S/J5OWnh+9k5PKKZrvsQ5Ip5Ay2gjWyKKYLFGieQY 4hTUpfSXFwPzFrOwVxDbKLaORsXcYQpFnXo1KS0mTNAM+MI6MRxIpcqErar9Ml6jd+ON nqXd5OtScVYYps5iocIFzZLd9IqpVH7UFE/WMd3gvYerTvBcS5S5icmDwAxvOZ9JscTO NARg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=Pqmj3ClLJHm0NWuPcuK5T5mzzNcGqtnI3cr79Wbf/BE=; b=a9+Be8yMQhSZGi6gEFQX5rZ/E0bAgah7RDzq9GPwVcNcOXh7hsbRaw1iA8ibO3/l5j 9PEFNa06YHm2K90Q5pm/KVN2vqMiRjVDBwaDpQZWGVt7WMi9tEHZYHtDWstMcrAbT3DF KUbXsqdZCgwJ0WLvwTKQBlhOhbNvWD7XZNe0lJ8mR5jZ/ZzoKi7Uzt69bChGSsbJe5zh oUhJyvhsDHCTo9klplyJk3SmYwTDPxxL3Kl2GG0ozVOttSUSRxFjHWtj53Qhhf2rr6l1 YcpvVTzW120ivoGOvm8Yne0Ya4kTavK2/ApPcgn/TBXP/FrO5GmrScZMSCsSYBuQ53RE bjhg== X-Gm-Message-State: AOUpUlHlOn3RzoXQPP/kCaKf8unuOqdNXfVRP4oBLuPJU8Ib/jMf0vkY YYgk5+Ui343R/+a9ZhO27lDJgu3jdVjvhRzYkI0= X-Google-Smtp-Source: AA+uWPwQPHjJpNg+Nt3nD0HCqFo3QCVn25BfaNtwuVjkAYuDcR2sYfxf/WjddMfk/u5g3ccOZpuW2+x+A1FkTwV+M9M= X-Received: by 2002:a37:2916:: with SMTP id p22-v6mr20182515qkh.327.1534264535796; Tue, 14 Aug 2018 09:35:35 -0700 (PDT) MIME-Version: 1.0 Received: by 2002:a0c:c3cc:0:0:0:0:0 with HTTP; Tue, 14 Aug 2018 09:35:35 -0700 (PDT) In-Reply-To: <58d21bac-5a31-85df-4b9f-05815b64f465@linux.ibm.com> References: <20180809041856.1547-1-ravi.bangoria@linux.ibm.com> <20180809041856.1547-4-ravi.bangoria@linux.ibm.com> <95a1221e-aecc-42be-5239-a2c2429be176@linux.ibm.com> <20180813115019.GB28360@redhat.com> <20180813131723.GC28360@redhat.com> <58d21bac-5a31-85df-4b9f-05815b64f465@linux.ibm.com> From: Song Liu Date: Tue, 14 Aug 2018 09:35:35 -0700 Message-ID: Subject: Re: [PATCH v8 3/6] Uprobes: Support SDT markers having reference count (semaphore) To: Ravi Bangoria Cc: Oleg Nesterov , Srikar Dronamraju , Steven Rostedt , mhiramat@kernel.org, Peter Zijlstra , mingo@redhat.com, acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, namhyung@kernel.org, open list , ananth@linux.vnet.ibm.com, Alexis Berlemont , 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 13, 2018 at 9:37 PM, Ravi Bangoria wrote: > Hi Song, > > On 08/13/2018 10:42 PM, Song Liu wrote: >> On Mon, Aug 13, 2018 at 6:17 AM, Oleg Nesterov wrote: >>> On 08/13, Ravi Bangoria wrote: >>>> >>>>> But damn, process creation (exec) is trivial. We could add a new uprobe_exec() >>>>> hook and avoid delayed_uprobe_install() in uprobe_mmap(). >>>> >>>> I'm sorry. I didn't get this. >>> >>> Sorry for confusion... >>> >>> I meant, if only exec*( could race with _register(), we could add another uprobe >>> hook which updates all (delayed) counters before return to user-mode. >>> >>>>> Afaics, the really problematic case is dlopen() which can race with _register() >>>>> too, right? >>>> >>>> dlopen() should internally use mmap() right? So what is the problem here? Can >>>> you please elaborate. >>> >>> What I tried to say is that we can't avoid uprobe_mmap()->delayed_uprobe_install() >>> because dlopen() can race with _register() too, just like exec. >>> >>> Oleg. >>> >> >> How about we do delayed_uprobe_install() per file? Say we keep a list >> of delayed_uprobe >> in load_elf_binary(). Then we can install delayed_uprobe after loading >> all sections of the >> file. > > I'm not sure if I totally understood the idea. But how this approach can > solve dlopen() race with _register()? > > Rather, making delayed_uprobe_list an mm field seems simple and effective > idea to me. The only overhead will be list_empty(mm->delayed_list) check. > > Please let me know if I misunderstood you. > > Thanks, > Ravi I misunderstood the problem here. I guess mm->delayed_list is the easiest solution of the race condition. Thanks, Song