Sergey Bugaev 4717009e3e Kernel: Hold less locks when receiving ICMP packets ...

* We don't have to lock the "all IPv4 sockets" in exclusive mode, shared mode is
  enough for just reading the list (as opposed to modifying it).
* We don't have to lock socket's own lock at all, the IPv4Socket::did_receive()
  implementation takes care of this.
* Most importantly, we don't have to hold the "all IPv4 sockets" across the
  IPv4Socket::did_receive() call(s). We can copy the current ICMP socket list
  while holding the lock, then release the lock, and then call
  IPv4Socket::did_receive() on all the ICMP sockets in our list.

These changes fix a deadlock triggered by receiving ICMP messages when using tap
networking setup (as opposed to QEMU's default user/SLIRP networking) on the host.

2021-02-12 15:37:28 +01:00

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