[PATCH] [RFC] maple_tree: reduce stack usage with gcc-9 and earlier

[Arnd Bergmann]

From: Arnd Bergmann <arnd@xxxxxxxx>

gcc-10 changed the way inlining works to be less aggressive, but
older versions run into an oversized stack frame warning whenever
CONFIG_KASAN_STACK is enabled, as that forces variables from
inlined callees to be non-overlapping:

lib/maple_tree.c: In function 'mas_wr_bnode':
lib/maple_tree.c:4320:1: error: the frame size of 1424 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]

Change the annotations on mas_store_b_node() and mas_commit_b_node()
to explicitly forbid inlining in this configuration, which is
the same behavior that newer versions already have.

Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Cc: kasan-dev@xxxxxxxxxxxxxxxx
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
 lib/maple_tree.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 5e9703189259..646297cae5d1 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -146,6 +146,13 @@ struct maple_subtree_state {
 	struct maple_big_node *bn;
 };
 
+#ifdef CONFIG_KASAN_STACK
+/* Prevent mas_wr_bnode() from exceeding the stack frame limit */
+#define noinline_for_kasan noinline_for_stack
+#else
+#define noinline_for_kasan inline
+#endif
+
 /* Functions */
 static inline struct maple_node *mt_alloc_one(gfp_t gfp)
 {
@@ -2107,7 +2114,7 @@ static inline void mas_bulk_rebalance(struct ma_state *mas, unsigned char end,
  *
  * Return: The actual end of the data stored in @b_node
  */
-static inline void mas_store_b_node(struct ma_wr_state *wr_mas,
+static noinline_for_kasan void mas_store_b_node(struct ma_wr_state *wr_mas,
 		struct maple_big_node *b_node, unsigned char offset_end)
 {
 	unsigned char slot;
@@ -3579,7 +3586,7 @@ static inline bool mas_reuse_node(struct ma_wr_state *wr_mas,
  * @b_node: The maple big node
  * @end: The end of the data.
  */
-static inline int mas_commit_b_node(struct ma_wr_state *wr_mas,
+static noinline_for_kasan int mas_commit_b_node(struct ma_wr_state *wr_mas,
 			    struct maple_big_node *b_node, unsigned char end)
 {
 	struct maple_node *node;
-- 
2.39.1