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From: Lawrence Stewart <lstewart@FreeBSD.org>
Date: Mon, 13 Jul 2009 11:59:38 +0000 (UTC)
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Subject: cvs commit: src/sys/netinet tcp_sack.c
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lstewart    2009-07-13 11:59:38 UTC

  FreeBSD src repository

  Modified files:
    sys/netinet          tcp_sack.c 
  Log:
  SVN rev 195655 on 2009-07-13 11:59:38Z by lstewart
  
  Fix a race in the manipulation of the V_tcp_sack_globalholes global variable,
  which is currently not protected by any type of lock. When triggered, the bug
  would sometimes cause a panic when the TCP activity to an affected machine
  eventually slowed during a lull. The panic only occurs if INVARIANTS is compiled
  into the kernel, and has laid dormant for some time as a result of INVARIANTS
  being off by default except in FreeBSD-CURRENT.
  
  Switch to atomic operations in the locations where the variable is changed.
  Reads have not been updated to be protected by atomics, so there is a
  possibility of accounting errors in any given calculation where the variable is
  read. This is considered unlikely to occur in the wild, and will not cause
  serious harm on rare occasions where it does.
  
  Thanks to Robert Watson for debugging help.
  
  Reported by:    Kamigishi Rei <spambox at haruhiism dot net>
  Tested by:      Kamigishi Rei <spambox at haruhiism dot net>
  Reviewed by:    silby
  Approved by:    re (rwatson), kensmith (mentor temporarily unavailable)
  
  Revision  Changes    Path
  1.50      +2 -2      src/sys/netinet/tcp_sack.c