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=-4.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 518A3C48BE6 for ; Mon, 14 Jun 2021 20:30:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2CE9060FEA for ; Mon, 14 Jun 2021 20:30:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235536AbhFNUcY (ORCPT ); Mon, 14 Jun 2021 16:32:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51224 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234626AbhFNUcV (ORCPT ); Mon, 14 Jun 2021 16:32:21 -0400 Received: from mail-lj1-x22e.google.com (mail-lj1-x22e.google.com [IPv6:2a00:1450:4864:20::22e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 41C5CC061574; Mon, 14 Jun 2021 13:30:16 -0700 (PDT) Received: by mail-lj1-x22e.google.com with SMTP id c11so21906496ljd.6; Mon, 14 Jun 2021 13:30:16 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=/hnnncj7vzT6xrqQOtqK95hj1J3zQcIX0GD5ENHwYGs=; b=Sf/C6jQAejQ7QgbqyKgzN5j9RKIEIYJ5qRCASL/CGyadtbYOldpIm39EE+PC/IKXuf P8tJ6EJIryYoPG1+Fy2KA1D+ZHhcsLap7Y8VKeDn1AnPFqUxZ+rNJ4xuw8fmFAzS0n7F DbJG3wesc2UbKZsKsj+rHOO9uXSbn86OdUlQalg6+3hnLjAJ/AhVrRQjFzYaXK+ynlfZ IwG6Lx/G3uFxuU+hEOIPhrvgt/LS6Bg1CNUWUv3FIcqdaSjwP8Aim+e1DsTbUoskgPFH 07q4i7KlMmaO5Q4Z4XqSLYnOmdSguEV8WZjDyE3riaIy+dUZzZ6zOsOy/NnRPDA1TL14 TEig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=/hnnncj7vzT6xrqQOtqK95hj1J3zQcIX0GD5ENHwYGs=; b=TaZwYsptwrnXkdtpktSroOvEm+uT1+8XrfqQuL5Nmwk3+iToA6UsxnNUySDmNxtw68 aWDE/8tt5H5kOKtrPcdiiMrtkZFglPtXq9y4rXYhbMSuhpQOlonGZM1/LyDHxoyp+u87 Z/Ym+S+/LxDY3WdjRk1U7lixWHB+wB1SgibXHuTq4jQsup3DvOQR0GMue8uGCYvSMIYs MLPSSYY8gHG9hdG0oWq9JmlT+WCAsY5OBYdkpywhN/5bM07ji+++K8Sv1yL0hsuDOO0V 0FdghefG/ct1VtFsUqgpiSyUtbOgN7nWrFHE7jUn8w08TP1qc1SvqO4FaoUg7S1J1Ngn leiA== X-Gm-Message-State: AOAM531lu4WKRlrtEvnVdxQmxEXB5cgoy8bPud54jCSuH83HFfopfyQU ddhAiXX/cVV5FgKLNLr9hkM= X-Google-Smtp-Source: ABdhPJwIAkPoePHhzl7KL6lSn4/Ac+1NH4oqgxaj2w/nYPwdN8ocoZPG8abc63Nw9LkwP5vtZ0O+8w== X-Received: by 2002:a2e:9959:: with SMTP id r25mr14631258ljj.317.1623702614608; Mon, 14 Jun 2021 13:30:14 -0700 (PDT) Received: from localhost.localdomain ([94.103.229.24]) by smtp.gmail.com with ESMTPSA id d4sm1574079lfk.295.2021.06.14.13.30.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 14 Jun 2021 13:30:14 -0700 (PDT) Date: Mon, 14 Jun 2021 23:30:11 +0300 From: Pavel Skripkin To: Dongliang Mu Cc: alex.aring@gmail.com, "David S. Miller" , Jakub Kicinski , linux-kernel , linux-wpan@vger.kernel.org, netdev@vger.kernel.org, stefan@datenfreihafen.org, syzkaller-bugs , syzbot+b80c9959009a9325cdff@syzkaller.appspotmail.com, Dan Carpenter , Greg KH Subject: Re: Suggestions on how to debug kernel crashes where printk and gdb both does not work Message-ID: <20210614233011.79ebe38a@gmail.com> In-Reply-To: References: <20210614163401.52807197@gmail.com> <20210614172512.799db10d@gmail.com> <20210614174727.6a38b584@gmail.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-suse-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 14 Jun 2021 23:04:03 +0800 Dongliang Mu wrote: > On Mon, Jun 14, 2021 at 10:47 PM Pavel Skripkin > wrote: > > > > On Mon, 14 Jun 2021 22:40:55 +0800 > > Dongliang Mu wrote: > > > > > On Mon, Jun 14, 2021 at 10:25 PM Pavel Skripkin > > > wrote: > > > > > > > > On Mon, 14 Jun 2021 22:19:10 +0800 > > > > Dongliang Mu wrote: > > > > > > > > > On Mon, Jun 14, 2021 at 9:34 PM Pavel Skripkin > > > > > wrote: > > > > > > > > > > > > On Mon, 14 Jun 2021 21:22:43 +0800 > > > > > > Dongliang Mu wrote: > > > > > > > > > > > > > Dear kernel developers, > > > > > > > > > > > > > > I was trying to debug the crash - memory leak in > > > > > > > hwsim_add_one [1] recently. However, I encountered a > > > > > > > disgusting issue: my breakpoint and printk/pr_alert in the > > > > > > > functions that will be surely executed do not work. The > > > > > > > stack trace is in the following. I wrote this email to > > > > > > > ask for some suggestions on how to debug such cases? > > > > > > > > > > > > > > Thanks very much. Looking forward to your reply. > > > > > > > > > > > > > > > > > > > Hi, Dongliang! > > > > > > > > > > > > This bug is not similar to others on the dashboard. I spent > > > > > > some time debugging it a week ago. The main problem here, > > > > > > that memory allocation happens in the boot time: > > > > > > > > > > > > > [] kernel_init+0xc/0x1a7 > > > > > > > init/main.c:1447 > > > > > > > > > > > > > > > > Oh, nice catch. No wonder why my debugging does not work. :( > > > > > > > > > > > and reproducer simply tries to > > > > > > free this data. You can use ftrace to look at it. Smth like > > > > > > this: > > > > > > > > > > > > $ echo 'hwsim_*' > $TRACE_DIR/set_ftrace_filter > > > > > > > > > > Thanks for your suggestion. > > > > > > > > > > Do you have any conclusions about this case? If you have found > > > > > out the root cause and start writing patches, I will turn my > > > > > focus to other cases. > > > > > > > > No, I had some busy days and I have nothing about this bug for > > > > now. I've just traced the reproducer execution and that's all :) > > > > > > > > I guess, some error handling paths are broken, but Im not sure > > > > > > In the beginning, I agreed with you. However, after I manually > > > checked functions: hwsim_probe (initialization) and hwsim_remove > > > (cleanup), then things may be different. The cleanup looks > > > correct to me. I would like to debug but stuck with the debugging > > > process. > > > > > > And there is another issue: the cleanup function also does not > > > output anything or hit the breakpoint. I don't quite understand > > > it since the cleanup is not at the boot time. > > > > > > Any idea? > > > > > > > Output from ftrace (syzkaller repro): > > > > root@syzkaller:~# cat /sys/kernel/tracing/trace > > # tracer: function_graph > > # > > # CPU DURATION FUNCTION CALLS > > # | | | | | | | > > 1) | hwsim_del_radio_nl() { > > 1) | hwsim_del() { > > 1) | hwsim_edge_unsubscribe_me() { > > 1) ! 310.041 us | hwsim_free_edge(); > > 1) ! 665.221 us | } > > 1) * 52999.05 us | } > > 1) * 53035.38 us | } > > > > Cleanup function is not the case, I think :) > > It seems like I spot the incorrect cleanup function (hwsim_remove is > the right one is in my mind). Let me learn how to use ftrace to log > the executed functions and then discuss this case with you guys. > Hmmm, I think, there is a mess with lists. I just want to share my debug results, I have no idea about the fix for now. In hwsim_probe() edge for phy->idx = 1 is allocated, then reproduces sends a request to delete phy with idx == 0, so this check in hwsim_edge_unsubscribe_me(): if (e->endpoint->idx == phy->idx) { ... clean up code ... } won't be passed and edge won't be freed (because it was allocated for phy with idx == 1). Allocated edge for phy 1 becomes leaked after hwsim_del(). I can't really see the code where phy with idx == 1 can be deleted from list... Maybe, it's kmemleak bug. Similar strange case was with this one https://syzkaller.appspot.com/bug?id=3a325b8389fc41c1bc94de0f4ac437ed13cce584. I find it strange, that I could reach leaked pointers after kmemleak reported a leak. Im not familiar with kmemleak internals and I might be wrong With regards, Pavel Skripkin