Message-ID: <20250116162056.186121-1-mrpre@163.com>
Date: Fri, 17 Jan 2025 00:20:56 +0800
From: Jiayuan Chen <mrpre@....com>
To: linux-doc@...r.kernel.org,
	rdunlap@...radead.org,
	corbet@....net
Cc: tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	x86@...nel.org,
	hpa@...or.com,
	linux-kernel@...r.kernel.org,
	Jiayuan Chen <mrpre@....com>
Subject: [PATCH v2] docs/arch: remove deprecated function name

The dumpstack.c file has undergone many modifications, and the
print_context_stack() function was removed or rewritten a long time ago,
so it's better to remove the incorrect guidance.

I also want to preserve the original contributor info by keeping email
adress and name.

Signed-off-by: Jiayuan Chen <mrpre@....com>
---
 Documentation/arch/x86/kernel-stacks.rst | 51 +++++++++---------------
 1 file changed, 18 insertions(+), 33 deletions(-)

diff --git a/Documentation/arch/x86/kernel-stacks.rst b/Documentation/arch/x86/kernel-stacks.rst
index 738671a4070b..f780f4b09761 100644
--- a/Documentation/arch/x86/kernel-stacks.rst
+++ b/Documentation/arch/x86/kernel-stacks.rst
@@ -112,41 +112,26 @@ 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
-stares at print_context_stack() and the whole machinery in and around
-arch/x86/kernel/dumpstack.c.
+keeps popping up, here provides guidance about it. It helps if the reader
+stares at printk_stack_addressk() and its callers and pay special
+attention to the 'reliable' parameter ('?' basically means that the
+address is unreliable).
 
-Adapted from Ingo's mail, Message-ID: <20150521101614.GA10889@...il.com>:
+The detail about '?' can be found in the comments within dumpstack.c:
+::
 
-We always scan the full kernel stack for return addresses stored on
-the kernel stack(s) [1]_, from stack top to stack bottom, and print out
-anything that 'looks like' a kernel text address.
+    /*
+     * Scan the stack, printing any text addresses we find.  At the
+     * same time, follow proper stack frames with the unwinder.
+     *
+     * Addresses found during the scan which are not reported by
+     * the unwinder are considered to be additional clues which are
+     * sometimes useful for debugging and are prefixed with '?'.
+     * This also serves as a failsafe option in case the unwinder
+     * goes off in the weeds.
+     */
 
-If it fits into the frame pointer chain, we print it without a question
-mark, knowing that it's part of the real backtrace.
 
-If the address does not fit into our expected frame pointer chain we
-still print it, but we print a '?'. It can mean two things:
+You can also get more info from Ingo's original emal [1]_
 
- - either the address is not part of the call chain: it's just stale
-   values on the kernel stack, from earlier function calls. This is
-   the common case.
-
- - or it is part of the call chain, but the frame pointer was not set
-   up properly within the function, so we don't recognize it.
-
-This way we will always print out the real call chain (plus a few more
-entries), regardless of whether the frame pointer was set up correctly
-or not - but in most cases we'll get the call chain right as well. The
-entries printed are strictly in stack order, so you can deduce more
-information from that as well.
-
-The most important property of this method is that we _never_ lose
-information: we always strive to print _all_ addresses on the stack(s)
-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.
-
-.. [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.
+.. [1] https://lore.kernel.org/lkml/20150521101614.GA10889@gmail.com/
-- 
2.43.5

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