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From: Warner Losh <imp@FreeBSD.org>
Date: Fri, 10 Oct 2008 17:49:47 +0000 (UTC)
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Subject: cvs commit: src/sys/kern subr_bus.c
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imp         2008-10-10 17:49:47 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             subr_bus.c 
  Log:
  SVN rev 183750 on 2008-10-10 17:49:47Z by imp
  
  Close, but not eliminate, a race condition.  It is one that properly
  designed drivers would never hit, but was exposed in diving into
  another problem...
  
  When expanding the devclass array, free the old memory after updating
  the pointer to the new memory.  For the following single race case,
  this helps:
  
          allocate new memory
          copy to new memory
          free old memory
  <interrupt>                             read pointer to freed memory
          update pointer to new memory
  
  Now we do
          allocate new memory
          copy to new memory
          update pointer to new memory
          free old memory
  
  Which closes this problem, but doesn't even begin to address the
  multicpu races, which all should be covered by Giant at the moment,
  but likely aren't completely.
  
  Note: reviewers were ok with this fix, but suggested the use case
  wasn't one we wanted to encourage.
  
  Reviewed by:    jhb, scottl.
  
  Revision  Changes    Path
  1.210     +6 -4      src/sys/kern/subr_bus.c