On Mon, 28 Nov 2022, Nathan Chancellor wrote:
Portions of upstream commit a4055888629b ("mm/memcg: warning on !memcg after readahead page charged") were backported as commit cfe575954ddd ("mm: add VM_WARN_ON_ONCE_PAGE() macro"). Unfortunately, the backport did not account for the lack of commit 33def8498fdd ("treewide: Convert macro and uses of __section(foo) to __section("foo")") in kernels prior to 5.10, resulting in the following orphan section warnings on PowerPC clang builds with CONFIG_DEBUG_VM=y:
powerpc64le-linux-gnu-ld: warning: orphan section `".data.once"' from `mm/huge_memory.o' being placed in section `".data.once"' powerpc64le-linux-gnu-ld: warning: orphan section `".data.once"' from `mm/huge_memory.o' being placed in section `".data.once"' powerpc64le-linux-gnu-ld: warning: orphan section `".data.once"' from `mm/huge_memory.o' being placed in section `".data.once"'
This is a difference between how clang and gcc handle macro stringification, which was resolved for the kernel by not stringifying the argument to the __section() macro. Since that change was deemed not suitable for the stable kernels by commit 59f89518f510 ("once: fix section mismatch on clang builds"), do that same thing as that change and remove the quotes from the argument to __section().
Fixes: cfe575954ddd ("mm: add VM_WARN_ON_ONCE_PAGE() macro") Signed-off-by: Nathan Chancellor nathan@kernel.org
Yes indeed: thanks Nathan, sorry about that.
Acked-by: Hugh Dickins hughd@google.com
As far as I can tell, this should be applied to 5.4 and earlier. It should apply cleanly but let me know if not.
I think it should be good for 4.19 also, but I don't know what happens or would happen in 4.14 and 4.9 trees, since those have no other example of .data.once or ".data.once" (and I've lost what little I ever knew of that linker script stuff).
Since we're not hearing complaints about those (or are you?), perhaps those trees are not clang-ready in other ways, and for gcc it all works out by itself: I'd be inclined to just leave them as is myself, if there are no reports of breakage; but you may know better, and prefer to remove the ' __section(".data.once")' from the 4.14 and 4.9 versions.
include/linux/mmdebug.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h index 5d0767cb424a..4ed52879ce55 100644 --- a/include/linux/mmdebug.h +++ b/include/linux/mmdebug.h @@ -38,7 +38,7 @@ void dump_mm(const struct mm_struct *mm); } \ } while (0) #define VM_WARN_ON_ONCE_PAGE(cond, page) ({ \
- static bool __section(".data.once") __warned; \
- static bool __section(.data.once) __warned; \ int __ret_warn_once = !!(cond); \ \ if (unlikely(__ret_warn_once && !__warned)) { \
base-commit: 4d2a309b5c28a2edc0900542d22fec3a5a22243b
2.38.1