Documentation: x86: convert kernel-stacks to reST

This converts the plain text documentation to reStructuredText format and
add it to Sphinx TOC tree. No essential content change.
Signed-off-by: Changbin Du <changbin.du@gmail.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/x86/index.rst

@@ -11,3 +11,4 @@ x86-specific Documentation
    boot
    topology
    exception-tables
+   kernel-stacks

Documentation/x86/kernel-stacks → Documentation/x86/kernel-stacks.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Kernel Stacks
+=============
+
 Kernel stacks on x86-64 bit
----------------------------
+===========================
 
 Most of the text from Keith Owens, hacked by AK
 
@@ -57,7 +63,7 @@ IST events with the same code to be nested.  However in most cases, the
 stack size allocated to an IST assumes no nesting for the same code.
 If that assumption is ever broken then the stacks will become corrupt.
 
-The currently assigned IST stacks are :-
+The currently assigned IST stacks are:
 
 * DOUBLEFAULT_STACK.  EXCEPTION_STKSZ (PAGE_SIZE).
 
@@ -98,7 +104,7 @@ For more details see the Intel IA32 or AMD AMD64 architecture manuals.
 
 
 Printing backtraces on x86
---------------------------
+==========================
 
 The question about the '?' preceding function names in an x86 stacktrace
 keeps popping up, here's an indepth explanation. It helps if the reader
@@ -108,7 +114,7 @@ arch/x86/kernel/dumpstack.c.
 Adapted from Ingo's mail, Message-ID: <20150521101614.GA10889@gmail.com>:
 
 We always scan the full kernel stack for return addresses stored on
-the kernel stack(s) [*], from stack top to stack bottom, and print out
+the kernel stack(s) [1]_, from stack top to stack bottom, and print out
 anything that 'looks like' a kernel text address.
 
 If it fits into the frame pointer chain, we print it without a question
@@ -136,6 +142,6 @@ that look like kernel text addresses, so if debug information is wrong,
 we still print out the real call chain as well - just with more question
 marks than ideal.
 
-[*] For things like IRQ and IST stacks, we also scan those stacks, in
+.. [1] For things like IRQ and IST stacks, we also scan those stacks, in
        the right order, and try to cross from one stack into another
        reconstructing the call chain. This works most of the time.