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Message-ID: <CAEA6p_DpSr84cYu3pXqoHV=V=daSsbiOcnzsF+Kt0r4Wv_jmdg@mail.gmail.com>
Date: Wed, 20 Sep 2017 15:09:02 -0700
From: Wei Wang <weiwan@...gle.com>
To: Paweł Staszewski <pstaszewski@...are.pl>
Cc: Cong Wang <xiyou.wangcong@...il.com>,
Eric Dumazet <eric.dumazet@...il.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>
Subject: Re: Latest net-next from GIT panic
>>> 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
>
Thanks very much Pawel for the feedback.
I was looking into the code (specifically IPv4 part) and found that in
free_fib_info_rcu(), we call free_nh_exceptions() without holding the
fnhe_lock. I am wondering if that could cause some race condition on
fnhe->fnhe_rth_input/output so a double call on dst_dev_put() on the
same dst could be happening.
But as we call free_fib_info_rcu() only after the grace period, and
the lookup code which could potentially modify
fnhe->fnhe_rth_input/output all holds rcu_read_lock(), it seems
fine...
On Wed, Sep 20, 2017 at 2:25 PM, Paweł Staszewski <pstaszewski@...are.pl> wrote:
>
>
> 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
>
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