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From: Matt Dillon <dillon@FreeBSD.ORG>
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Date: Thu, 21 Jan 1999 21:49:41 -0800 (PST)
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To: cvs-committers@FreeBSD.ORG, cvs-all@FreeBSD.ORG
Subject: cvs commit: src/sys/vm vm_fault.c
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dillon      1999/01/21 21:49:40 PST

  Modified files:        (Branch: RELENG_3)
    sys/vm               vm_fault.c 
  Log:
      Backport from -4.x.  We are supposed to wait while the page is busy before
      messing with it, but the VM code was special-casing a m->busy page that
      was still valid ( i.e. usually a pageout ) and allowing it through.  The
      problem is that whatever m->busy'd the page is probably still depending on
      it not being messed with.  Specifically, I am thinking of the
      vm_pager_get_pages() code where the OBJT_VNODE pager converts PG_BUSY
      to m->busy for the read operation.    While this code may not be
      specifically broken for the case, it does initially set PG_BUSY and assume
      that it has the entire page to itself... but OBJT_VNODE converts it to
      m->busy.  It is just too dangerous to allow the special case optimization
      through.
  
      Removing the special optimization should have no discernable effect since
      pageout operates mark resident pmap pte's READ-ONLY rather then unmapping
      them, and so no fault normally occurs.
  
  Revision  Changes    Path
  1.93.2.1  +24 -9     src/sys/vm/vm_fault.c

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