Re: [patch] sched: unlocked context-switches

[David Mosberger]

>>>>> On Sat, 9 Apr 2005 09:07:38 +0200, Ingo Molnar <mingo@xxxxxxx> said:

  Ingo> * David Mosberger-Tang <David.Mosberger@xxxxxxx> 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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