Commit-ID: e77cb32558a7bd0e996b7e203158a7fbf1a663fb Gitweb: https://git.kernel.org/tip/e77cb32558a7bd0e996b7e203158a7fbf1a663fb Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> AuthorDate: Fri, 22 Jun 2018 06:22:20 -0700 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Wed, 29 Aug 2018 08:54:14 -0700 doc: Add design documentation on interruption of NMI handlers Make Requirements.html talk about how NMI handlers can take what appear to RCU to be normal interrupts. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- Documentation/RCU/Design/Requirements/Requirements.html | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/Documentation/RCU/Design/Requirements/Requirements.html b/Documentation/RCU/Design/Requirements/Requirements.html index 49690228b1c6..089a8e8faac1 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.html +++ b/Documentation/RCU/Design/Requirements/Requirements.html @@ -2275,6 +2275,17 @@ he also kindly surprised me with <a href="https://lkml.kernel.org/g/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@xxxxxxxxxxxxxx";>an algorithm</a> that meets this requirement. +<p> +Furthermore, NMI handlers can be interrupted by what appear to RCU +to be normal interrupts. +One way that this can happen is for code that directly invokes +<tt>rcu_irq_enter()</tt> and </tt>rcu_irq_exit()</tt> to be called +from an NMI handler. +This astonishing fact of life prompted the current code structure, +which has <tt>rcu_irq_enter()</tt> invoking <tt>rcu_nmi_enter()</tt> +and <tt>rcu_irq_exit()</tt> invoking <tt>rcu_nmi_exit()</tt>. +And yes, I also learned of this requirement the hard way. + <h3><a name="Loadable Modules">Loadable Modules</a></h3> <p>
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