From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934066AbeEJGqe (ORCPT ); Thu, 10 May 2018 02:46:34 -0400 Received: from mail-pg0-f65.google.com ([74.125.83.65]:44271 "EHLO mail-pg0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756712AbeEJGqb (ORCPT ); Thu, 10 May 2018 02:46:31 -0400 X-Google-Smtp-Source: AB8JxZrGvn1o1VS59+gNWYjwWwRsP1qlJwyuvN5KH8zjer6r5yO7MHfPHSwMCbsfizkWUJqUpePWxCI3tZKghYucAW8= MIME-Version: 1.0 In-Reply-To: References: <7fd7e3b3-77b1-0936-b169-d08b946bedc7@iogearbox.net> <991243e2-e7c2-f2b2-72b9-d37b0d569b3b@gmail.com> <5973966e-fcd9-7ee5-a9c4-b79d22c1b9dd@nokia.com> <20180220162622.GA32068@hmswarspite.think-freely.org> <7d98027d-e810-a079-49c5-0bf8beef390e@nokia.com> From: Dmitry Vyukov Date: Thu, 10 May 2018 08:46:08 +0200 Message-ID: Subject: Re: net: hang in unregister_netdevice: waiting for lo to become free To: Dan Streetman Cc: Tommi Rantala , Neil Horman , Xin Long , David Ahern , Daniel Borkmann , Cong Wang , David Miller , Eric Dumazet , Willem de Bruijn , Jakub Kicinski , Rasmus Villemoes , netdev , LKML , Alexey Kuznetsov , Hideaki YOSHIFUJI , syzkaller , Dan Streetman , "Eric W. Biederman" , Alexey Kodanev , Marcelo Ricardo Leitner , linux-sctp@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 16, 2018 at 9:42 PM, Dan Streetman wrote: >>>>> On Wed, Feb 21, 2018 at 3:53 PM, Tommi Rantala >>>>> wrote: >>>>>> On 20.02.2018 18:26, Neil Horman wrote: >>>>>>> >>>>>>> On Tue, Feb 20, 2018 at 09:14:41AM +0100, Dmitry Vyukov wrote: >>>>>>>> >>>>>>>> On Tue, Feb 20, 2018 at 8:56 AM, Tommi Rantala >>>>>>>> wrote: >>>>>>>>> >>>>>>>>> On 19.02.2018 20:59, Dmitry Vyukov wrote: >>>>>>>>>> >>>>>>>>>> Is this meant to be fixed already? I am still seeing this on the >>>>>>>>>> latest upstream tree. >>>>>>>>>> >>>>>>>>> >>>>>>>>> These two commits are in v4.16-rc1: >>>>>>>>> >>>>>>>>> commit 4a31a6b19f9ddf498c81f5c9b089742b7472a6f8 >>>>>>>>> Author: Tommi Rantala >>>>>>>>> Date: Mon Feb 5 21:48:14 2018 +0200 >>>>>>>>> >>>>>>>>> sctp: fix dst refcnt leak in sctp_v4_get_dst >>>>>>>>> ... >>>>>>>>> Fixes: 410f03831 ("sctp: add routing output fallback") >>>>>>>>> Fixes: 0ca50d12f ("sctp: fix src address selection if using >>>>>>>>> secondary >>>>>>>>> addresses") >>>>>>>>> >>>>>>>>> >>>>>>>>> commit 957d761cf91cdbb175ad7d8f5472336a4d54dbf2 >>>>>>>>> Author: Alexey Kodanev >>>>>>>>> Date: Mon Feb 5 15:10:35 2018 +0300 >>>>>>>>> >>>>>>>>> sctp: fix dst refcnt leak in sctp_v6_get_dst() >>>>>>>>> ... >>>>>>>>> Fixes: dbc2b5e9a09e ("sctp: fix src address selection if using >>>>>>>>> secondary >>>>>>>>> addresses for ipv6") >>>>>>>>> >>>>>>>>> >>>>>>>>> I guess we missed something if it's still reproducible. >>>>>>>>> >>>>>>>>> I can check it later this week, unless someone else beat me to it. >>>>>>>> >>>>>>>> >>>>>>>> Hi Tommi, >>>>>>>> >>>>>>>> Hmmm, I can't claim that it's exactly the same bug. Perhaps it's >>>>>>>> another one then. But I am still seeing these: >>>>>>>> >>>>>>>> [ 58.799130] unregister_netdevice: waiting for lo to become free. >>>>>>>> Usage count = 4 >>>>>>>> [ 60.847138] unregister_netdevice: waiting for lo to become free. >>>>>>>> Usage count = 4 >>>>>>>> [ 62.895093] unregister_netdevice: waiting for lo to become free. >>>>>>>> Usage count = 4 >>>>>>>> [ 64.943103] unregister_netdevice: waiting for lo to become free. >>>>>>>> Usage count = 4 >>>>>>>> >>>>>>>> on upstream tree pulled ~12 hours ago. >>>>>>>> >>>>>>> Can you write a systemtap script to probe dev_hold, and dev_put, printing >>>>>>> out a >>>>>>> backtrace if the device name matches "lo". That should tell us >>>>>>> definitively if >>>>>>> the problem is in the same location or not >>>>>> >>>>>> >>>>>> Hi Dmitry, I tested with the reproducer and the kernel .config file that you >>>>>> sent in the first email in this thread: >>>>>> >>>>>> With 4.16-rc2 unable to reproduce. >>>>>> >>>>>> With 4.15-rc9 bug reproducible, and I get "unregister_netdevice: waiting for >>>>>> lo to become free. Usage count = 3" >>>>>> >>>>>> With 4.15-rc9 and Alexey's "sctp: fix dst refcnt leak in sctp_v6_get_dst()" >>>>>> cherry-picked on top, unable to reproduce. >>>>>> >>>>>> >>>>>> Is syzkaller doing something else now to trigger the bug...? >>>>>> Can you still trigger the bug with the same reproducer? >>>>> >>>>> Hi Neil, Tommi, >>>>> >>>>> Reviving this old thread about "unregister_netdevice: waiting for lo >>>>> to become free. Usage count = 3" hangs. >>>>> I still did not have time to deep dive into what happens there (too >>>>> many bugs coming from syzbot). But this still actively happens and I >>>>> suspect accounts to a significant portion of various hang reports, >>>>> which are quite unpleasant. >>>>> >>>>> One idea that could make it all simpler: >>>>> >>>>> Is this wait loop in netdev_wait_allrefs() supposed to wait for any >>>>> prolonged periods of time under any non-buggy conditions? E.g. more >>>>> than 1-2 minutes? >>>>> If it only supposed to wait briefly for things that already supposed >>>>> to be shutting down, and we add a WARNING there after some timeout, >>>>> then syzbot will report all info how/when it happens, hopefully >>>>> extracting reproducers, and all the nice things. >>>>> But this WARNING should not have any false positives under any >>>>> realistic conditions (e.g. waiting for arrival of remote packets with >>>>> large timeouts). >>>>> >>>>> Looking at some task hung reports, it seems that this code holds some >>>>> mutexes, takes workqueue thread and prevents any progress with >>>>> destruction of other devices (and net namespace creation/destruction), >>>>> so I guess it should not wait for any indefinite periods of time? >>>> >>>> I'm working on this currently: >>>> https://bugs.launchpad.net/ubuntu/zesty/+source/linux/+bug/1711407 >>>> >>>> I added a summary of what I've found to be the cause (or at least, one >>>> possible cause) of this: >>>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1711407/comments/72 >>>> >>>> I'm working on a patch to work around the main side-effect of this, >>>> which is hanging while holding the global net mutex. Hangs will still >>>> happen (e.g. if a dst leaks) but should not affect anything else, >>>> other than a leak of the dst and its net namespace. >>>> >>>> Fixing the dst leaks is important too, of course, but a dst leak (or >>>> other cause) shouldn't break the entire system. >>> >>> Leaking some memory is definitely better than hanging the system. >>> >>> So I've made syzkaller to recognize "unregister_netdevice: waiting for >>> (.*) to become free" as a kernel bug: >>> https://github.com/google/syzkaller/commit/7a67784ca8bdc3b26cce2f0ec9a40d2dd9ec9396 >>> Unfortunately it does not make it catch these bugs because creating a >>> net namespace per test is too damn slow, so namespaces are reused for >>> lots of tests and when/if it's eventually destroyed it's already too >>> late to find root cause. >>> >>> But I've run a one-off experiment with prompt net namespace >>> destruction and syzkaller was able to easily extract a C reproducer: >>> https://gist.githubusercontent.com/dvyukov/d571e8fff24e127ca48a8c4790d42bfa/raw/52050e93ba9afbb5126b9d7bb39b7e71a82af016/gistfile1.txt >>> >>> On upstream 16e205cf42da1f497b10a4a24f563e6c0d574eec with this config: >>> https://gist.githubusercontent.com/dvyukov/9663c57443adb21f2795b92ef0829d62/raw/bbea0652e23746096dd56855a28f6c681aebcdee/gistfile1.txt >>> >>> this gives me: >>> >>> [ 83.183198] unregister_netdevice: waiting for lo to become free. >>> Usage count = 9 >>> [ 85.231202] unregister_netdevice: waiting for lo to become free. >>> Usage count = 9 >>> ... >>> [ 523.511205] unregister_netdevice: waiting for lo to become free. >>> Usage count = 9 >>> ... >>> >>> This is generated from this syzkaller program: >>> >>> r0 = socket$inet6(0xa, 0x1, 0x84) >>> setsockopt$inet6_IPV6_XFRM_POLICY(r0, 0x29, 0x23, >>> &(0x7f0000000380)={{{@in6=@remote={0xfe, 0x80, [], 0xbb}, >>> @in=@dev={0xac, 0x14, 0x14}, 0x0, 0x0, 0x0, 0x0, 0xa}, {}, {}, 0x0, >>> 0x0, 0x1}, {{@in=@local={0xac, 0x14, 0x14, 0xaa}, 0x0, 0x32}, 0x0, >>> @in=@local={0xac, 0x14, 0x14, 0xaa}, 0x3504}}, 0xe8) >>> bind$inet6(r0, &(0x7f0000000000)={0xa, 0x4e20}, 0x1c) >>> connect$inet(r0, &(0x7f0000000040)={0x2, 0x4e20, @dev={0xac, 0x14, >>> 0x14, 0xd}}, 0x10) >>> syz_emit_ethernet(0x3e, &(0x7f00000001c0)={@local={[0xaa, 0xaa, 0xaa, >>> 0xaa, 0xaa], 0xaa}, @dev={[0xaa, 0xaa, 0xaa, 0xaa, 0xaa]}, [], >>> {@ipv6={0x86dd, {0x0, 0x6, "50a09c", 0x8, 0xffffff11, 0x0, >>> @remote={0xfe, 0x80, [], 0xbb}, @local={0xfe, 0x80, [], 0xaa}, {[], >>> @udp={0x0, 0x4e20, 0x8}}}}}}, &(0x7f0000000040)) >>> >>> So this seems to be related to IPv6 and/or xfrm and is potentially >>> caused by external packets (that syz_emit_ethernet call). >> >> >> >> Here is another repro which seems to be a different bug (note that it >> requires fault injection): >> >> https://gist.githubusercontent.com/dvyukov/1c56623016cc4c24a69d433c5114ad5b/raw/530478f571b195193101b912aa646948528baa8e/gistfile1.txt >> >> Dan, do you mind taking a look at them? Fixing these should eliminate >> root causes of these hangs/leaks. > > Yep I will look at them, thanks for the reproducers. Hi Dan, Any updates on this? syzbot is hitting this all the time.