[PATCH 1/1] lib: do limited memory accounting for modules with ARCH_NEEDS_WEAK_PER_CPU

[Suren Baghdasaryan]

ARCH_NEEDS_WEAK_PER_CPU does not allow percpu variable definitions inside
a function, therefore memory allocation profiling can't use it. This
definition is used only for modules, so we still can account core kernel
allocations and for modules we can do limited allocation accounting by
charging all of them to a single counter. This is not ideal but better
than no accounting at all.

Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202403290334.USWrYrMw-lkp@xxxxxxxxx/
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
 include/linux/alloc_tag.h | 14 ++++++++++++--
 lib/alloc_tag.c           |  3 +++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 100ddf66eb8e..e867461585ff 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -68,9 +68,17 @@ static inline struct alloc_tag *ct_to_alloc_tag(struct codetag *ct)
 /*
  * When percpu variables are required to be defined as weak, static percpu
  * variables can't be used inside a function (see comments for DECLARE_PER_CPU_SECTION).
+ * Instead we will accound all module allocations to a single counter.
  */
-#error "Memory allocation profiling is incompatible with ARCH_NEEDS_WEAK_PER_CPU"
-#endif
+DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
+
+#define DEFINE_ALLOC_TAG(_alloc_tag)						\
+	static struct alloc_tag _alloc_tag __used __aligned(8)			\
+	__section("alloc_tags") = {						\
+		.ct = CODE_TAG_INIT,						\
+		.counters = &_shared_alloc_tag };
+
+#else /* ARCH_NEEDS_WEAK_PER_CPU */
 
 #define DEFINE_ALLOC_TAG(_alloc_tag)						\
 	static DEFINE_PER_CPU(struct alloc_tag_counters, _alloc_tag_cntr);	\
@@ -79,6 +87,8 @@ static inline struct alloc_tag *ct_to_alloc_tag(struct codetag *ct)
 		.ct = CODE_TAG_INIT,						\
 		.counters = &_alloc_tag_cntr };
 
+#endif /* ARCH_NEEDS_WEAK_PER_CPU */
+
 DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 			mem_alloc_profiling_key);
 
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index e24830c44783..b37e3430ed92 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -10,6 +10,9 @@
 
 static struct codetag_type *alloc_tag_cttype;
 
+DEFINE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
+EXPORT_SYMBOL(_shared_alloc_tag);
+
 DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 			mem_alloc_profiling_key);
 

base-commit: d4cd6840d1dc25963aa10ef5e5b1d01876baebf2
-- 
2.44.0.478.gd926399ef9-goog