cvs commit: src/sys/kern uipc_socket2.c

[Robert Watson]

rwatson     2005-05-27 17:16:43 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             uipc_socket2.c 
  Log:
  In the current world order, each socket has two mutexes: a mutex
  that protects socket and receive socket buffer state, and a second
  mutex to protect send socket buffer state.  In some places, the
  mutex shared between the socket and receive socket buffer will be
  acquired twice, once by each layer, resulting in some
  inconsistency, but providing the abstraction benefit of being able
  to more easily separate the two mutexes in the future if desired.
  
  When transitioning a socket to the SS_ISDISCONNECTING or
  SS_ISDISCONNECTED states, grab the socket/receive socket buffer lock
  once rather than grabbing it as the socket lock, modifying socket
  state, then grabbing a second time as the receive lock in order to
  modify the socket buffer state to indicate no further data can be
  read.  This change is believed to close a race between the change in
  socket state and the change in socket buffer state, which for a
  remotely initiated close on a UNIX domain socket, resulted in
  soreceive() returning ENOTCONN rather than an EOF condition.
  
  A similar race still exists in the case of send, however, and is
  harder to fix as the socket and send socket buffer mutexes are not
  the same, and we would like to avoid holding combinations of socket
  mutexes over sb_upcall until we've finished clarifying the locking
  protocol for upcalls.
  
  This change has the side affect of reducing the number of mutex
  operations to initiate disconnect or perform disconnect on a
  socket by two.
  
  PR:             78824
  Rerported by:   Marc Olzheim <marcolz at stack.nl>
  MFC after:      2 weeks
  
  Revision  Changes    Path
  1.146     +6 -13     src/sys/kern/uipc_socket2.c