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Commit e77cb325 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 5b394b2d

Documentation/RCU/Design/Requirements/Requirements.html

+11 −0
Original line number Diff line number Diff line
@@ -2275,6 +2275,17 @@ he also kindly surprised me with 
<a href="https://lkml.kernel.org/g/CALCETrXSY9JpW3uE6H8WYk81sg56qasA2aqmjMPsq5dOtzso=g@mail.gmail.com">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>