Hello, I am reading 2.4.22 kernel code on TCP/IP networking. And I don't understand why the following scenario will not occur: 1. user thread calls read which in turn calls tcp_recvmsg() on an established socket 2. tcp_recvmsg() sees that no data is available on receive_queue, installs prequeue 3. tcp_recvmsg() continues and prepare to sleep because it has not seen any data, but it has not entered tcp_data_wait() yet. 4. suddenly at this moment a packet comes in 5. the bottom half calls bh_lock_sock, see that sock->lock.users == 1, adds the packet to backlog queue 6. the bottom half exits 7. tcp_recvmsg calls tcp_data_wait() to sleep 8. in release_sock() of tcp_data_wait, backlog queue is processed by tcp_v4_do_rcv() which calls tcp_rcv_established() 9. in tcp_rcv_established(), as prequeue is installed, packets are directly copied to user context and nothing gets queued to sk->receive_queue, so eaten == 1 10. at the end of tcp_rcv_established(), because eaten == 1, sk->data_ready(sk, 0); is *not* called 11. backlog queue processing finished, return to release_sock in step 8. 12. continue tcp_data_wait() in step 7, see that receive_queue is NULL, goes to sleep If the above situation occurs, the user thread waiting for data will go to sleep even though incoming packets have been processed and data have been copied. Obviously it was not the case. I wonder at which step did I miss something. Thanks a lot. Wen -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
