percpu: fix clang modpost section mismatch

pcpu_build_alloc_info() is an __init function that makes a call to
cpumask_clear_cpu(). With CONFIG_GCOV_PROFILE_ALL enabled, the inline
heuristics are modified and such cpumask_clear_cpu() which is marked
inline doesn't get inlined. Because it works on mask in __initdata,
modpost throws a section mismatch error.

Arnd sent a patch with the flatten attribute as an alternative [2]. I've
added it to compiler_attributes.h.

modpost complaint:
  WARNING: modpost: vmlinux.o(.text+0x735425): Section mismatch in reference from the function cpumask_clear_cpu() to the variable .init.data:pcpu_build_alloc_info.mask
  The function cpumask_clear_cpu() references
  the variable __initdata pcpu_build_alloc_info.mask.
  This is often because cpumask_clear_cpu lacks a __initdata
  annotation or the annotation of pcpu_build_alloc_info.mask is wrong.

clang output:
  mm/percpu.c:2724:5: remark: cpumask_clear_cpu not inlined into pcpu_build_alloc_info because too costly to inline (cost=725, threshold=325) [-Rpass-missed=inline]

[1] https://lore.kernel.org/linux-mm/202012220454.9F6Bkz9q-lkp@intel.com/
[2] https://lore.kernel.org/lkml/CAK8P3a2ZWfNeXKSm8K_SUhhwkor17jFo3xApLXjzfPqX0eUDUA@mail.gmail.com/

Reported-by: kernel test robot <lkp@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>

diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index ea5e04e..c043b8d 100644 (file)
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -211,6 +211,12 @@
 #endif
 
 /*
+ * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes
+ * clang: https://clang.llvm.org/docs/AttributeReference.html#flatten
+ */
+# define __flatten                     __attribute__((flatten))
+
+/*
  * Note the missing underscores.
  *
  *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-noinline-function-attribute

diff --git a/mm/percpu.c b/mm/percpu.c
index 80f8f88..6596a0a 100644 (file)
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2663,7 +2663,7 @@ early_param("percpu_alloc", percpu_alloc_setup);
  * On success, pointer to the new allocation_info is returned.  On
  * failure, ERR_PTR value is returned.
  */
-static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
+static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info(
                                size_t reserved_size, size_t dyn_size,
                                size_t atom_size,
                                pcpu_fc_cpu_distance_fn_t cpu_distance_fn)