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doc: Update NMI-RCU.rst
This commit updates NMI-RCU.rst to highlight the ancient heritage of
the example code and to discourage wanton compiler "optimizations".
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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Documentation/RCU/NMI-RCU.rst
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Documentation/RCU/NMI-RCU.rst
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it is possible to use RCU to provide dynamic non-maskable interrupt
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handlers, as well as dynamic irq handlers. This document describes
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how to do this, drawing loosely from Zwane Mwaikambo's NMI-timer
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work in "arch/x86/kernel/traps.c".
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work in an old version of "arch/x86/kernel/traps.c".
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The relevant pieces of code are listed below, each followed by a
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brief explanation::
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This same sad story can happen on other CPUs when using
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a compiler with aggressive pointer-value speculation
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optimizations.
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optimizations. (But please don't!)
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More important, the rcu_dereference_sched() makes it
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clear to someone reading the code that the pointer is