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    FromDavid Mosberger <>
    DateSat, 9 Apr 2005 00:15:37 -0700
    SubjectRe: [patch] sched: unlocked context-switches
    >>>>> On Sat, 9 Apr 2005 09:07:38 +0200, Ingo Molnar <mingo@elte.hu> said:
    
      Ingo> * David Mosberger-Tang <David.Mosberger@acm.org> wrote:
    
      >> > The ia64_switch_to() code includes a section that can change a
      >> > pinned MMU mapping (when the stack for the new process is in a
      >> > different granule from the stack for the old process).  The code
      >> > beyond the ".map" label in arch/ia64/kernel/entry.S includes the
      >> > comment:
      >> Also, there was a nasty dead-lock that could trigger if the
      >> context-switch was interrupted by a TLB flush IPI.  I don't
      >> remember the details offhand, but I'm pretty sure it had to do
      >> with switch_mm(), so I suspect it may not be enough to disable
      >> irqs just for ia64_switch_to().  Tread with care!
    
      Ingo> we'll see. The patch certainly needs more testing. Generally
      Ingo> we do switch_mm()'s outside of the scheduler as well, without
      Ingo> disabling interrupts.
    
    Yes, of course.  The deadlock was due to context-switching, not
    switch_mm() per se.  Hopefully someone else beats me to remembering
    the details before Monday.
    
    	--david
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