netdev - Re: Latest net-next from GIT panic

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Message-ID: <26e8b899-d8b1-caa4-436b-e23ffe384b0f@itcare.pl>
Date:   Wed, 20 Sep 2017 23:24:03 +0200
From:   Paweł Staszewski <pstaszewski@...are.pl>
To:     Cong Wang <xiyou.wangcong@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     Wei Wang <weiwan@...gle.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: Latest net-next from GIT panic



W dniu 2017-09-20 o 23:10, Paweł Staszewski pisze:
>
>
> W dniu 2017-09-20 o 21:23, Paweł Staszewski pisze:
>>
>>
>> W dniu 2017-09-20 o 21:13, Paweł Staszewski pisze:
>>>
>>>
>>> W dniu 2017-09-20 o 20:36, Cong Wang pisze:
>>>> On Wed, Sep 20, 2017 at 11:30 AM, Eric Dumazet 
>>>> <eric.dumazet@...il.com> wrote:
>>>>> On Wed, 2017-09-20 at 11:22 -0700, Cong Wang wrote:
>>>>>> but dmesg at this time shows nothing about interfaces or flaps.
>>>>>>
>>>>>> This is very odd.
>>>>>>
>>>>>> We only free netdevice in free_netdev() and it is only called when
>>>>>> we unregister a netdevice. Otherwise pcpu_refcnt is impossible
>>>>>> to be NULL.
>>>>> If there is a missing dev_hold() or one dev_put() in excess,
>>>>> this would allow the netdev to be freed too soon.
>>>>>
>>>>> -> Use after free.
>>>>> memory holding netdev could be reallocated-cleared by some other 
>>>>> kernel
>>>>> user.
>>>>>
>>>> Sure, but only unregister could trigger a free. If there is no 
>>>> unregister,
>>>> like what Pawel claims, then there is no free, the refcnt just goes to
>>>> 0 but the memory is still there.
>>>>
>>> About possible mistake from my side with bisect - i can judge too 
>>> early that some bisect was good
>>> the road was:
>>> git bisect start
>>> # bad: [ac7b75966c9c86426b55fe1c50ae148aa4571075] Merge tag 
>>> 'pinctrl-v4.13-1' of 
>>> git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl
>>> git bisect bad ac7b75966c9c86426b55fe1c50ae148aa4571075
>>> # good: [e24dd9ee5399747b71c1d982a484fc7601795f31] Merge branch 
>>> 'next' of 
>>> git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security
>>> git bisect good e24dd9ee5399747b71c1d982a484fc7601795f31
>>> # bad: [9cc9a5cb176ccb4f2cda5ac34da5a659926f125f] datapath: Avoid 
>>> using stack larger than 1024.
>>> git bisect bad 9cc9a5cb176ccb4f2cda5ac34da5a659926f125f
>>> # good: [073cf9e20c333ab29744717a23f9e43ec7512a20] Merge branch 
>>> 'udp-reduce-cache-pressure'
>>> git bisect good 073cf9e20c333ab29744717a23f9e43ec7512a20
>>> # bad: [8abd5599a520e9f188a750f1bde9dde5fb856230] Merge branch 
>>> 's390-net-updates-part-2'
>>> git bisect bad 8abd5599a520e9f188a750f1bde9dde5fb856230
>>> # good: [2fae5d0e647c6470d206e72b5fc24972bb900f70] Merge branch 
>>> 'bpf-ctx-narrow'
>>> git bisect good 2fae5d0e647c6470d206e72b5fc24972bb900f70
>>> # good: [41500c3e2a19ffcf40a7158fce1774de08e26ba2] rds: tcp: remove 
>>> cp_outgoing
>>> git bisect good 41500c3e2a19ffcf40a7158fce1774de08e26ba2
>>> # bad: [8917a777be3ba566377be05117f71b93a5fd909d] tcp: md5: add 
>>> TCP_MD5SIG_EXT socket option to set a key address prefix
>>> git bisect bad 8917a777be3ba566377be05117f71b93a5fd909d
>>> # good: [4a6ce2b6f2ecabbddcfe47e7cf61dd0f00b10e36] net: introduce a 
>>> new function dst_dev_put()
>>>
>>> And currently have this running for about 4 hours without problems.
>>>
>>>
>>>
>>> git bisect good 4a6ce2b6f2ecabbddcfe47e7cf61dd0f00b10e36
>>> # bad: [a4c2fd7f78915a0d7c5275e7612e7793157a01f2] net: remove 
>>> DST_NOCACHE flag
>>>
>>> Here for sure - panic
>>>
>>> git bisect bad a4c2fd7f78915a0d7c5275e7612e7793157a01f2
>>> # bad: [ad65a2f05695aced349e308193c6e2a6b1d87112] ipv6: call 
>>> dst_hold_safe() properly
>>> git bisect bad ad65a2f05695aced349e308193c6e2a6b1d87112
>>> # good: [9df16efadd2a8a82731dc76ff656c771e261827f] ipv4: call 
>>> dst_hold_safe() properly
>>> git bisect good 9df16efadd2a8a82731dc76ff656c771e261827f
>>> # bad: [1cfb71eeb12047bcdbd3e6730ffed66e810a0855] ipv6: take 
>>> dst->__refcnt for insertion into fib6 tree
>>>
>>> im not 100% sure tor last two
>>> Will test them again starting from
>>> [95c47f9cf5e028d1ae77dc6c767c1edc8a18025b] ipv4: call dst_dev_put() 
>>> properly
>>>
>>>
>>> git bisect bad 1cfb71eeb12047bcdbd3e6730ffed66e810a0855
>>> # bad: [b838d5e1c5b6e57b10ec8af2268824041e3ea911] ipv4: mark 
>>> DST_NOGC and remove the operation of dst_free()
>>>
>>>
>>>
>>> git bisect bad b838d5e1c5b6e57b10ec8af2268824041e3ea911
>>> # first bad commit: [b838d5e1c5b6e57b10ec8af2268824041e3ea911] ipv4: 
>>> mark DST_NOGC and remove the operation of dst_free()
>>>
>>>
>>>
>> What i can say more
>> I can reproduce this on any server with similar configuration
>> the difference can be teamd instead of bonding
>> ixgbe or i40e and mlx5
>> Same problems
>>
>> vlans - more or less prefixes learned from bgp -> zebra -> netlink -> 
>> kernel
>> But normally in lab when using only plain routing no bgpd and about 
>> 128 vlans - with 128 routes - cant reproduce this - this apperas only 
>> with bgp - minimum where i can reproduce this was about 130k prefixes 
>> with about 286 nexthops
>>
>>
>>
>>
> bisected again and same result:
> b838d5e1c5b6e57b10ec8af2268824041e3ea911 is the first bad commit
> commit b838d5e1c5b6e57b10ec8af2268824041e3ea911
> Author: Wei Wang <weiwan@...gle.com>
> Date:   Sat Jun 17 10:42:32 2017 -0700
>
>     ipv4: mark DST_NOGC and remove the operation of dst_free()
>
>     With the previous preparation patches, we are ready to get rid of the
>     dst gc operation in ipv4 code and release dst based on refcnt only.
>     So this patch adds DST_NOGC flag for all IPv4 dst and remove the 
> calls
>     to dst_free().
>     At this point, all dst created in ipv4 code do not use the dst gc
>     anymore and will be destroyed at the point when refcnt drops to 0.
>
>     Signed-off-by: Wei Wang <weiwan@...gle.com>
>     Acked-by: Martin KaFai Lau <kafai@...com>
>     Signed-off-by: David S. Miller <davem@...emloft.net>
>
> :040000 040000 9b7e7fb641de6531fc7887473ca47ef7cb6a11da 
> 831a73b71d3df1755f3e24c0d3c86d7a93fd55e2 M      net
>
> Will add now version 2 of patch from Eric and we will see
>
>
after adding patch
perf top catch
    PerfTop:   77159 irqs/sec  kernel:99.7%  exact:  0.0% [4000Hz 
cycles],  (all, 40 CPUs)
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

     60.95%  [kernel]            [k] dev_put.part.6
      4.00%  [kernel]            [k] ixgbe_poll
      3.63%  [kernel]            [k] irq_entries_start
      1.22%  [kernel]            [k] fib_table_lookup
      1.15%  [kernel]            [k] do_raw_spin_lock
      1.05%  [kernel]            [k] ixgbe_xmit_frame_ring
      1.04%  [kernel]            [k] lookup
      0.87%  [kernel]            [k] eth_type_trans


no panic on console - rebooting to check logs