git: kernel - Fix network lockup due to msgport bug

[Matthew Dillon]

commit ddb06db22c9a473b5bbb374b988cd074eda75a80
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date:   Thu Feb 21 18:14:45 2013 -0800

    kernel - Fix network lockup due to msgport bug
    
    * Netisr threads (i.e. arp thread) which issue route table updates
      use a synchronous netmsg from a 'spin' type port to a 'thread' type
      port.
    
      When going spin->thread, the lwkt_thread_putport*() code was not
      using an atomic op to manipulate ms_flags.  This could interfere
      with the originator on the spin port issuing a lwkt_spin_waitmsg()
      and cause one or more flags to be lost.
    
      Ensure that lwkt_thread_putport*() uses atomic ops when manipulating
      ms_flags.
    
    * Another serious issue is that the lwkt_*_waitmsg() code was testing
      MSGF_QUEUED outside of its port lock.  This flag can only be tested
      while the port is locked.
    
    * lwkt_thread_replyport() must use an atomic op when setting
      MSGF_INTRANSIT and MSGF_REPLY to avoid SMP races on ms_flags
      updates.
    
    * lwkt_thread_replyport() requires a critical section against
      possible preemption when adjusting ms_flags.
    
    * lwkt_forwardmsg() does not need a critical section.
    
    * Other notes: Not all ms_flags manipulation needs an atomic op.  For
      example, when initializing a new message or when a lock is held to
      rendezvous at a reply port when replying.  However, all 'put' and 'wait'
      interactions on messages absolutely require atomic ops when manipulating
      ms_flags.
    
      Finally, note that all msgport queue operations use atomic ops to
      adjust MSGF_QUEUED when adding or removing a message to a port queue.

Summary of changes:
 sys/kern/lwkt_msgport.c | 61 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 41 insertions(+), 20 deletions(-)

http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/ddb06db22c9a473b5bbb374b988cd074eda75a80


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