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Message-ID: <20191029100605.GI20975@paulmck-ThinkPad-P72>
Date: Tue, 29 Oct 2019 03:06:05 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: madhuparnabhowmik04@...il.com
Cc: paulmck@...nel.org, joel@...lfernandes.org, corbet@....net,
linux-doc@...r.kernel.org, rcu@...r.kernel.org,
linux-kernel@...r.kernel.org,
linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] Documentation: RCU: NMI-RCU: Converted NMI-RCU.txt to
NMI-RCU.rst.
On Tue, Oct 29, 2019 at 03:12:52AM +0530, madhuparnabhowmik04@...il.com wrote:
> From: Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>
>
> This patch converts NMI-RCU from txt to rst format.
> Also adds NMI-RCU in the index.rst file.
>
> Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik04@...il.com>
Applied for further review, thank you! Assuming review goes well,
I will be pushing this for v5.6 (not the upcoming merge window, but
the one after it).
Thanx, Paul
> ---
> .../RCU/{NMI-RCU.txt => NMI-RCU.rst} | 53 ++++++++++---------
> Documentation/RCU/index.rst | 1 +
> 2 files changed, 29 insertions(+), 25 deletions(-)
> rename Documentation/RCU/{NMI-RCU.txt => NMI-RCU.rst} (73%)
>
> diff --git a/Documentation/RCU/NMI-RCU.txt b/Documentation/RCU/NMI-RCU.rst
> similarity index 73%
> rename from Documentation/RCU/NMI-RCU.txt
> rename to Documentation/RCU/NMI-RCU.rst
> index 881353fd5bff..da5861f6a433 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
> --
> 2.17.1
>
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