[PATCH 3/3] kasan: add KASAN_RCU_STACK_RECORD documentation

[Walter Wu]

This adds the documentation for the KASAN_RCU_STACK_RECORD config option.

Signed-off-by: Walter Wu <walter-zh.wu@xxxxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
---
 Documentation/dev-tools/kasan.rst | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index c652d740735d..368ff0dad0d7 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -281,3 +281,24 @@ unmapped. This will require changes in arch-specific code.
 
 This allows ``VMAP_STACK`` support on x86, and can simplify support of
 architectures that do not have a fixed module region.
+
+CONFIG_KASAN_RCU_STACK_RECORD
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+With CONFIG_KASAN_RCU_STACK_RECORD, when call_rcu() is called, it will
+store the call_rcu() call stack into slub alloc meta-data. The goal
+is to print call_rcu() information in KASAN report. It is helpful for
+use-after-free or double free memory issue.
+
+Record first and last call_rcu() call stack and print two call_rcu()
+call stack in KASAN report.
+
+This option doesn't increase the cost of memory consumption, we add two
+call_rcu() call stack into struct kasan_alloc_meta and size is 8 bytes.
+Remove the free track from struct kasan_alloc_meta and size is 8 bytes.
+So we don't enlarge the slub meta-data size.
+
+This option is only suitable for generic KASAN. Because the free track
+is stored in freed object. so free track is valid information only when
+it exists in the quarantine. If the slub object is in-use state, then
+KASAN report doesn't print call_rcu() free track information.
-- 
2.18.0