diff options
| -rw-r--r-- | Documentation/RCU/NMI-RCU.rst (renamed from Documentation/RCU/NMI-RCU.txt) | 53 | ||||
| -rw-r--r-- | Documentation/RCU/index.rst | 1 |
2 files changed, 29 insertions, 25 deletions
diff --git a/Documentation/RCU/NMI-RCU.txt b/Documentation/RCU/NMI-RCU.rst index 881353fd5bff..180958388ff9 100644 --- a/Documentation/RCU/NMI-RCU.txt +++ b/Documentation/RCU/NMI-RCU.rst @@ -1,4 +1,7 @@ +.. _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(); @@ -98,24 +102,23 @@ 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 - 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 - just after the new handler was set might see the pointer - to the new NMI handler, but the old pre-initialized - version of the handler's data. + 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 + just after the new handler was set might see the pointer + to the new NMI handler, but the old pre-initialized + version of the handler's data. - This same sad story can happen on other CPUs when using - a compiler with aggressive pointer-value speculation - optimizations. + This same sad story can happen on other CPUs when using + a compiler with aggressive pointer-value speculation + optimizations. - More important, the rcu_dereference_sched() makes it - clear to someone reading the code that the pointer is - being protected by RCU-sched. + More important, the rcu_dereference_sched() makes it + clear to someone reading the code that the pointer is + being protected by RCU-sched. diff --git a/Documentation/RCU/index.rst b/Documentation/RCU/index.rst index 8d20d44f8fd4..627128c230dc 100644 --- a/Documentation/RCU/index.rst +++ b/Documentation/RCU/index.rst @@ -10,6 +10,7 @@ RCU concepts arrayRCU rcu listRCU + NMI-RCU UP Design/Memory-Ordering/Tree-RCU-Memory-Ordering |