[PATCH v4 1/3] kernel.h: disable type-checks in container_of() for Sparse

[Masahiro Yamada]

When I tried to enable BUILD_BUG_ON for Sparse, the kbuild test robot
reported lots of "unknown expression" warnings from container_of(),
which seemed false positive.

I addressed this in [1], but fixing Sparse is the right thing to do.

The issue was fixed by Sparse commit 0eb8175d3e9c ("fix expansion of
function designator"), but it will take time until the fixed version
of Sparse is widely available.

Disable the container_of() type checks for Sparse for now.

[1] https://lore.kernel.org/lkml/1542623503-3755-1-git-send-email-yamada.masahiro@xxxxxxxxxxxxx/

Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
---

Changes in v4:
  - New patch

Changes in v3: None
Changes in v2: None

 include/linux/kernel.h | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index d6aac75..d8c4adb 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -985,6 +985,21 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
 #define __CONCAT(a, b) a ## b
 #define CONCATENATE(a, b) __CONCAT(a, b)
 
+/*
+ * TODO:
+ * Sparse emits "unknown expression" warnings.
+ * It was fixed by commit 0eb8175d3e9c0d20354763d07ce3d4c0e543d988 in Sparse.
+ * Remove the following workaround when the fixed Sparse is widely available.
+ */
+#ifdef __CHECKER__
+#define TYPE_CHECK_CONTAINER_OF(ptr, type, member)	do {} while (0)
+#else
+#define TYPE_CHECK_CONTAINER_OF(ptr, type, member) \
+	BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) &&	\
+			 !__same_type(*(ptr), void),			\
+			 "pointer type mismatch in container_of()")
+#endif
+
 /**
  * container_of - cast a member of a structure out to the containing structure
  * @ptr:	the pointer to the member.
@@ -994,9 +1009,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
  */
 #define container_of(ptr, type, member) ({				\
 	void *__mptr = (void *)(ptr);					\
-	BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) &&	\
-			 !__same_type(*(ptr), void),			\
-			 "pointer type mismatch in container_of()");	\
+	TYPE_CHECK_CONTAINER_OF(ptr, type, member);			\
 	((type *)(__mptr - offsetof(type, member))); })
 
 /**
@@ -1009,9 +1022,7 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
  */
 #define container_of_safe(ptr, type, member) ({				\
 	void *__mptr = (void *)(ptr);					\
-	BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) &&	\
-			 !__same_type(*(ptr), void),			\
-			 "pointer type mismatch in container_of()");	\
+	TYPE_CHECK_CONTAINER_OF(ptr, type, member);			\
 	IS_ERR_OR_NULL(__mptr) ? ERR_CAST(__mptr) :			\
 		((type *)(__mptr - offsetof(type, member))); })
 
-- 
2.7.4