netdev - Re: Latest net-next from GIT panic

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Date:   Wed, 20 Sep 2017 23:25:44 +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 23:24, Paweł Staszewski pisze:
>
>
> 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
>
>
Nothing logged