Re: [PATCH 1/4] selftests/mm: remove flaky header check

Kevin Brodsky
2025-12-17T09:58:57Z

On 17/12/2025 04:18, Yunsheng Lin wrote:
> On 2025/12/16 22:26, Kevin Brodsky wrote:
>> Commit 96ed62ea0298 ("mm: page_frag: fix a compile error when kernel
>> is not compiled") introduced a check to avoid attempting to build
>> the page_frag module if <linux/page_frag_cache.h> is missing.
>>
>> Unfortunately this check only works if KDIR points to
>> /lib/modules/... or an in-tree kernel build. It always fails if KDIR
>> points to an out-of-tree build (i.e. when the kernel was built with
>> O=$KDIR make) because only generated headers are present under
>> $KDIR/include/ in that case.
>>
>> <linux/page_frag_cache.h> was added more than a year ago (v6.13) so
>> we can probably live without that check.
> As some commercial OS still uses v6.6, I am wondering if we need that

Fair point, I hadn't considered that kselftests are supposed to be
buildable against older stable kernels.

> check for a little longer, is it possible to do something like below to
> avoid the flaky check?
>
> @@ -46,7 +46,8 @@ CFLAGS += -U_FORTIFY_SOURCE
>
> KDIR ?= /lib/modules/$(shell uname -r)/build
> ifneq (,$(wildcard $(KDIR)/Module.symvers))
> -ifneq (,$(wildcard $(KDIR)/include/linux/page_frag_cache.h))
> +KSRC := $(shell readlink -f $(KDIR)/source 2>/dev/null || echo $(KDIR))
> +ifneq (,$(wildcard $(KSRC)/include/linux/page_frag_cache.h))
> TEST_GEN_MODS_DIR := page_frag
> else
> PAGE_FRAG_WARNING = "missing page_frag_cache.h, please use a newer kernel"

That seems reasonable, and it works for my out-of-tree setup.

Will do that in v2, shall I add your Suggested-by, or maybe Co-developed-by?

- Kevin