doc: Converted NMI-RCU.txt to NMI-RCU.rst. (6705cae4) · Commits · 戴 / test

Documentation/RCU/NMI-RCU.txt→Documentation/RCU/NMI-RCU.rst

+28 −25

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		.. _NMI_rcu_doc:

		Using RCU to Protect Dynamic NMI Handlers
		=========================================


		Although RCU is usually used to protect read-mostly data structures,
		@@ -9,7 +12,7 @@ work in "arch/x86/oprofile/nmi_timer_int.c" and in
		"arch/x86/kernel/traps.c".

		The relevant pieces of code are listed below, each followed by a
		brief explanation.
		brief explanation::

		static int dummy_nmi_callback(struct pt_regs *regs, int cpu)
		{
		@@ -18,12 +21,12 @@ brief explanation.

		The dummy_nmi_callback() function is a "dummy" NMI handler that does
		nothing, but returns zero, thus saying that it did nothing, allowing
		the NMI handler to take the default machine-specific action.
		the NMI handler to take the default machine-specific action::

		static nmi_callback_t nmi_callback = dummy_nmi_callback;

		This nmi_callback variable is a global function pointer to the current
		NMI handler.
		NMI handler::

		void do_nmi(struct pt_regs * regs, long error_code)
		{
		@@ -53,11 +56,12 @@ anyway. However, in practice it is a good documentation aid, particularly
		for anyone attempting to do something similar on Alpha or on systems
		with aggressive optimizing compilers.

		Quick Quiz: Why might the rcu_dereference_sched() be necessary on Alpha,
		given that the code referenced by the pointer is read-only?
		Quick Quiz:
		Why might the rcu_dereference_sched() be necessary on Alpha, given that the code referenced by the pointer is read-only?

		:ref:`Answer to Quick Quiz <answer_quick_quiz_NMI>`

		Back to the discussion of NMI and RCU...
		Back to the discussion of NMI and RCU::

		void set_nmi_callback(nmi_callback_t callback)
		{
		@@ -68,7 +72,7 @@ The set_nmi_callback() function registers an NMI handler. Note that any
		data that is to be used by the callback must be initialized up -before-
		the call to set_nmi_callback(). On architectures that do not order
		writes, the rcu_assign_pointer() ensures that the NMI handler sees the
		initialized values.
		initialized values::

		void unset_nmi_callback(void)
		{
		@@ -82,7 +86,7 @@ up any data structures used by the old NMI handler until execution
		of it completes on all other CPUs.

		One way to accomplish this is via synchronize_rcu(), perhaps as
		follows:
		follows::

		unset_nmi_callback();
		synchronize_rcu();
		@@ -98,13 +102,12 @@ to free up the handler's data as soon as synchronize_rcu() returns.
		Important note: for this to work, the architecture in question must
		invoke nmi_enter() and nmi_exit() on NMI entry and exit, respectively.

		.. _answer_quick_quiz_NMI:

		Answer to Quick Quiz

		Why might the rcu_dereference_sched() be necessary on Alpha, given
		that the code referenced by the pointer is read-only?
		Answer to Quick Quiz:
		Why might the rcu_dereference_sched() be necessary on Alpha, given that the code referenced by the pointer is read-only?

		Answer: The caller to set_nmi_callback() might well have
		The caller to set_nmi_callback() might well have
		initialized some data that is to be used by the new NMI
		handler. In this case, the rcu_dereference_sched() would
		be needed, because otherwise a CPU that received an NMI

Documentation/RCU/index.rst

+1 −0

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		@@ -10,6 +10,7 @@ RCU concepts
		arrayRCU
		rcu
		listRCU
		NMI-RCU
		UP

		Design/Memory-Ordering/Tree-RCU-Memory-Ordering

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