netdev - Re: 答复: [PATCH] net: clean the sk_frag.page of new cloned socket

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Date:   Thu, 25 Jan 2018 21:16:22 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "Li,Rongqing" <lirongqing@...du.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "edumazet@...gle.com" <edumazet@...gle.com>
Subject: Re: 答复: [PATCH] net: clean the sk_frag.page of new cloned socket

On Thu, Jan 25, 2018 at 7:14 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2018-01-26 at 02:09 +0000, Li,Rongqing wrote:
>
>>
>> crash> bt 8683
>> PID: 8683   TASK: ffff881faa088000  CPU: 10  COMMAND: "mynode"
>>  #0 [ffff881fff145e78] crash_nmi_callback at ffffffff81031712
>>  #1 [ffff881fff145e88] nmi_handle at ffffffff816cafe9
>>  #2 [ffff881fff145ec8] do_nmi at ffffffff816cb0f0
>>  #3 [ffff881fff145ef0] end_repeat_nmi at ffffffff816ca4a1
>>     [exception RIP: _raw_spin_lock_irqsave+62]
>>     RIP: ffffffff816c9a9e  RSP: ffff881fa992b990  RFLAGS: 00000002
>>     RAX: 0000000000004358  RBX: ffff88207ffd7e80  RCX: 0000000000004358
>>     RDX: 0000000000004356  RSI: 0000000000000246  RDI: ffff88207ffd7ee8
>>     RBP: ffff881fa992b990   R8: 0000000000000000   R9: 00000000019a16e6
>>     R10: 0000000000004d24  R11: 0000000000004000  R12: 0000000000000242
>>     R13: 0000000000004d24  R14: 0000000000000001  R15: 0000000000000000
>>     ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
>> --- <NMI exception stack> ---
>>  #4 [ffff881fa992b990] _raw_spin_lock_irqsave at ffffffff816c9a9e
>>  #5 [ffff881fa992b998] get_page_from_freelist at ffffffff8113ce5f
>>  #6 [ffff881fa992ba70] __alloc_pages_nodemask at ffffffff8113d15f
>>  #7 [ffff881fa992bba0] alloc_pages_current at ffffffff8117ab29
>>  #8 [ffff881fa992bbe8] sk_page_frag_refill at ffffffff815dd310
>>  #9 [ffff881fa992bc18] tcp_sendmsg at ffffffff8163e4f3
>> #10 [ffff881fa992bcd8] inet_sendmsg at ffffffff81668434
>> #11 [ffff881fa992bd08] sock_sendmsg at ffffffff815d9719
>> #12 [ffff881fa992be58] SYSC_sendto at ffffffff815d9c81
>> #13 [ffff881fa992bf70] sys_sendto at ffffffff815da6ae
>> #14 [ffff881fa992bf80] system_call_fastpath at ffffffff816d2189
>>
>
> Note that tcp_sendmsg() does not use sk->sk_frag, but the per task
> page.
>
> Unless something changes sk->sk_allocation, which a user application
> can not do.
>

Some kernel TCP socket uses atomic allocation, e.g.,
o2net_open_listening_sock().