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=-7.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 636CFC48BDF for ; Tue, 15 Jun 2021 10:37:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 362536115B for ; Tue, 15 Jun 2021 10:37:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231386AbhFOKjs (ORCPT ); Tue, 15 Jun 2021 06:39:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41434 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231324AbhFOKjr (ORCPT ); Tue, 15 Jun 2021 06:39:47 -0400 Received: from mail-ej1-x633.google.com (mail-ej1-x633.google.com [IPv6:2a00:1450:4864:20::633]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADFE2C061574; Tue, 15 Jun 2021 03:37:42 -0700 (PDT) Received: by mail-ej1-x633.google.com with SMTP id ce15so21705923ejb.4; Tue, 15 Jun 2021 03:37:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=MtrZlwOnKCiqTIsZyr9FcNUuCAAc8LVqPYmpZpunwBw=; b=sX/IKWWvBf7AJJgA801akMh10X6iRWyD4L4o2OhN3TDt0C155Zy2zLDzAogwg2Th2R FwZxMFoipKiLX0Aag8R9UtLARg/mp1xBS3Ly9RzC/DCbbWdr5wuQ5N4R+yAU62yViWzT gBzgIK0AKCKkWjcTsX1MPATcGpY6xSk7our/IYz2SJDi/pAkJzibdnOS5m2GIf5j6bSE QvUUo177tLuZBsufdLYeHqn/mtr00P/CI1whPol0ml+BV5s9rKwPbrAe1FXCl8eor12Q 9fB/VxOvlLWBG46Tkp0lNJuGW6o+k+cMY8UOmX6etz2eUq09n6S/Zzs+Tli5cPmttAOA 6QGg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=MtrZlwOnKCiqTIsZyr9FcNUuCAAc8LVqPYmpZpunwBw=; b=Ib0+JtrNEZ16IHN6Dr/d+FBaAxRy29JReLc/0t/gg7D5WELAyHdRCtlHUHuoN/ktPR 6B59ysoiRMzYy2712YgUsZOlv3JY0KPBSJElTZ5sSSQF3Q9kQuFPaeta5DW3w2tIW/9f uBNDa6yrRqf0FIXwAjQN+gFLiLqWQ7CZFQ833n98dvT6r8nVJxlk7NKAsZo2Qc40YKPj kc1GocHXtI9SYa7traI7GAWi/WVYRjdoH7RGDCJ/kICK4yRov6fIFZUttPhqJzxrzlHG PWhEs9iXz+5l2ITp3k50CwRdsHpYf0Sw7OyKoG4rt570CctFbrAK8aZaar/eCLJrJywo ReQg== X-Gm-Message-State: AOAM531KPjIKzwYMTzCJKWdjp5WEW3nk7Q06ga81v9NIetZhJLxHT+sx 6CER7Rfgig8huzm9S7UerwozTyIeOtEGAoZfzYU= X-Google-Smtp-Source: ABdhPJz7lnbIX2lahXzVLoe09HL55d69W8pMSWjbbe0rh+PguNFz7IkFzdIbTH5JBTGQEDu6oEaWFf5u6V4iu/GygDM= X-Received: by 2002:a17:906:4f10:: with SMTP id t16mr19512291eju.337.1623753461201; Tue, 15 Jun 2021 03:37:41 -0700 (PDT) MIME-Version: 1.0 References: <20210614163401.52807197@gmail.com> <20210614172512.799db10d@gmail.com> <20210614174727.6a38b584@gmail.com> <20210614233011.79ebe38a@gmail.com> In-Reply-To: <20210614233011.79ebe38a@gmail.com> From: Dongliang Mu Date: Tue, 15 Jun 2021 18:37:14 +0800 Message-ID: Subject: Re: Suggestions on how to debug kernel crashes where printk and gdb both does not work To: Pavel Skripkin 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 Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-wpan@vger.kernel.org On Tue, Jun 15, 2021 at 4:30 AM Pavel Skripkin wrote: > > 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... Thanks for sharing your debugging result. hwsim_phys | --------------------------------- | | sub0 (edges) sub1 (edges) ----> e (idx = 1) ----> e (idx = 0) hwsim_del_radio_nl will call hwsim_del to delete phy (idx:1). However, in this function, it only deletes the e in the edge list of sub1. Then it deletes phy (i.e., sub0) from the hwsim_phys list. So it leaves the e in the edge list of sub0 non-free. I proposed a patch and test it successfully in the syzbot dashboard. diff --git a/drivers/net/ieee802154/mac802154_hwsim.c b/drivers/net/ieee802154/mac802154_hwsim.c index da9135231c07..b05159cff33a 100644 --- a/drivers/net/ieee802154/mac802154_hwsim.c +++ b/drivers/net/ieee802154/mac802154_hwsim.c @@ -824,9 +824,16 @@ static int hwsim_add_one(struct genl_info *info, struct device *dev, static void hwsim_del(struct hwsim_phy *phy) { struct hwsim_pib *pib; + struct hwsim_edge *e; hwsim_edge_unsubscribe_me(phy); + // remove the edges in the list + list_for_each_entry_rcu(e, &phy->edges, list) { + list_del_rcu(&e->list); + hwsim_free_edge(e); + } + list_del(&phy->list); rcu_read_lock(); I will send a patch later. > > 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