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

[Yunsheng Lin <linyunsheng@huawei.com>]

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
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"

> 
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: Yunsheng Lin <linyunsheng@huawei.com>
> Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
> ---
>  tools/testing/selftests/mm/Makefile | 4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index eaf9312097f7..aba51fcac752 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -46,12 +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))
>  TEST_GEN_MODS_DIR := page_frag
>  else
> -PAGE_FRAG_WARNING = "missing page_frag_cache.h, please use a newer kernel"
> -endif
> -else
>  PAGE_FRAG_WARNING = "missing Module.symvers, please have the kernel built first"
>  endif
>