[V6 PATCH 6/6] Documentation: Add documentation for kernel.panic_on_io_nmi sysctl

[Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>]

kernel.panic_on_io_nmi sysctl was introduced by commit 5211a242d0cb
("x86: Add sysctl to allow panic on IOCK NMI error"), but its
documentation is missing. So, add it.

V6:
- Newly added

Signed-off-by: Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 Documentation/sysctl/kernel.txt |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index af70d15..235f804 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -551,6 +551,21 @@ the recommended setting is 60.
 
 ==============================================================
 
+panic_on_io_nmi:
+
+Controls the kernel's behavior when a CPU receives an NMI caused by
+an IO error.
+
+0: try to continue operation (default)
+
+1: panic immediately. The IO error triggered NMI indicates a serious
+   system condition, which could result in IO data corruption. Rather
+   than continuing, panicking might be a better choice. Some servers
+   issue this sort of NMI when the dump button is pushed, and you
+   can use this option to take a crash dump
+
+==============================================================
+
 panic_on_oops:
 
 Controls the kernel's behaviour when an oops or BUG is encountered.