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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sat, 9 Jan 2010 11:28:01 +0000 (UTC)
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Subject: cvs commit: src/sys/amd64/amd64 sys_machdep.c
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kib         2010-01-09 11:28:01 UTC

  FreeBSD src repository

  Modified files:
    sys/amd64/amd64      sys_machdep.c 
  Log:
  SVN rev 201890 on 2010-01-09 11:28:01Z by kib
  
  Set md_ldt (pointer to the LDT) after md_ldt_sd (system segment
  descriptor for the LDT) is populated. md_ldt is used by context-switch
  code as indicator that LDT segment register shall be loaded with
  GUSERLDT segment instead of 0, so context switch at the wrong time may
  cause attempt to load non-populated descriptor.
  
  Use store with the barrier to prevent other CPUs from seeing updated
  md_ldt but not seeing updated md_ldt_sd. Multithreaded process may
  context-switch to another thread of the process on another CPU and read
  md_ldt.
  
  MFC after:      1 week
  
  Revision  Changes    Path
  1.95      +2 -1      src/sys/amd64/amd64/sys_machdep.c