George Anzinger wrote:
Nick Piggin wrote:
George Anzinger wrote:
The NMI entry and exit code fiddles with bits in the preempt count.
If an NMI happens while some other code is doing the same, bits will
be lost. This patch removes this modify code from the NMI path till
we can come up with something better.
Humour me for a minute here...
NMI restores preempt_count back to its old value upon exit, right?
So what does a race case look like?
Normal code NMI
fetch preempt_count
add <----- interrupt here add and store then
subtract and store, darn!
store preempt_count
Ok, no problem.
The problem is in the RT code when PREEMPT_DEBUG is on. The tests for
reasonable counts fail because of the rather undefined state when NMI
picks up the word. The failure is on the NMI side...
So NMI changing the preempt count and restoring in the middle of a RWM
is not the problem. Thus I don't understand what the issue is. NMI
must undo all side effects. Does the PREEMPT_DEBUG code check the count
somewhere within the NMI handler? If so, shouldn't the proper fix be to
make that code aware that it could be running inside of an NMI and/or
ensure that code is not called from within the NMI handler?
Zach
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