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Posted to commits@nuttx.apache.org by GitBox <gi...@apache.org> on 2021/05/03 08:35:55 UTC

[GitHub] [incubator-nuttx] PetteriAimonen opened a new issue #3647: Race condition causes hang in tcp_send_unbuffered() when host closes socket quickly

PetteriAimonen opened a new issue #3647:
URL: https://github.com/apache/incubator-nuttx/issues/3647

I have observed this sequence of events, which happens only with specific software combination but then occurs within 30 minutes or so:

1. Host opens TCP connection to NuttX and sends HTTP request.
2. My code on NuttX responds with initial headers and starts preparing response payload.
3. My code calls `send()` while simultaneously host closes TCP connection.
4. TCP communication stops working, ping still works. With debugger I observe that `psock_tcp_send()` is stuck in `net_timedwait()`. Connection has `tcpstateflags = 9 (TCP_LAST_ACK)`, `unacked = 0` and `psock.s_flags = 0x83 (_SF_CLOSED | _SF_SEND)`.

My theory is that there is a window for race condition in `psock_tcp_send()` between the check for connection and when `net_lock()` is called. If a network device interrupt occurs in that window, it can change the socket to a closed state. Then the disconnect event or the data event never happen, and the callback does not get called.

I have attached a preliminary patch that appears to fix the problem for me. However it would be great if someone could review if this makes sense.

I am unable to reproduce the problem on newest NuttX git version due to the specific timing conditions needed, but based on reviewing the code the race condition seems to be present there also.

[nuttx_psock_tcp_send_patch.txt](https://github.com/apache/incubator-nuttx/files/6413704/nuttx_psock_tcp_send_patch.txt)

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[GitHub] [incubator-nuttx] PetteriAimonen commented on issue #3647: Race condition causes hang in tcp_send_unbuffered() when host closes socket quickly

Posted by GitBox <gi...@apache.org>.

PetteriAimonen commented on issue #3647:
URL: https://github.com/apache/incubator-nuttx/issues/3647#issuecomment-831114877


   Err.. that patch leaves net locked; have to amend further.


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[GitHub] [incubator-nuttx] PetteriAimonen commented on issue #3647: Race condition causes hang in tcp_send_unbuffered() when host closes socket quickly

Posted by GitBox <gi...@apache.org>.

PetteriAimonen commented on issue #3647:
URL: https://github.com/apache/incubator-nuttx/issues/3647#issuecomment-831670197


   @antmerlino Yes, the fix in #3647 works for me when backported to NuttX 7.26.


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[GitHub] [incubator-nuttx] PetteriAimonen removed a comment on issue #3647: Race condition causes hang in tcp_send_unbuffered() when host closes socket quickly

Posted by GitBox <gi...@apache.org>.

PetteriAimonen removed a comment on issue #3647:
URL: https://github.com/apache/incubator-nuttx/issues/3647#issuecomment-831114877


   Err.. that patch leaves net locked; have to amend further.


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[GitHub] [incubator-nuttx] antmerlino commented on issue #3647: Race condition causes hang in tcp_send_unbuffered() when host closes socket quickly

Posted by GitBox <gi...@apache.org>.

antmerlino commented on issue #3647:
URL: https://github.com/apache/incubator-nuttx/issues/3647#issuecomment-831494050


   @PetteriAimonen Can you see if my PR fixes the issue if you back-port what I did to whatever version you are running?
   


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[GitHub] [incubator-nuttx] antmerlino edited a comment on issue #3647: Race condition causes hang in tcp_send_unbuffered() when host closes socket quickly

Posted by GitBox <gi...@apache.org>.

antmerlino edited a comment on issue #3647:
URL: https://github.com/apache/incubator-nuttx/issues/3647#issuecomment-831494050


   @PetteriAimonen Can you see if my PR fixes the issue if you backport what I did to whatever version you are running?
   


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[GitHub] [incubator-nuttx] xiaoxiang781216 closed issue #3647: Race condition causes hang in tcp_send_unbuffered() when host closes socket quickly

Posted by GitBox <gi...@apache.org>.

xiaoxiang781216 closed issue #3647:
URL: https://github.com/apache/incubator-nuttx/issues/3647


   


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