linux-kernel - Re: [PATCH 4/4] mm/kasan: make kasan=on|off take effect for all three modes

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Message-Id: <20250806052231.619715-1-sj@kernel.org>
Date: Tue,  5 Aug 2025 22:22:31 -0700
From: SeongJae Park <sj@...nel.org>
To: Baoquan He <bhe@...hat.com>
Cc: SeongJae Park <sj@...nel.org>,
	linux-mm@...ck.org,
	ryabinin.a.a@...il.com,
	glider@...gle.com,
	andreyknvl@...il.com,
	dvyukov@...gle.com,
	vincenzo.frascino@....com,
	akpm@...ux-foundation.org,
	kasan-dev@...glegroups.com,
	linux-kernel@...r.kernel.org,
	kexec@...ts.infradead.org
Subject: Re: [PATCH 4/4] mm/kasan: make kasan=on|off take effect for all three modes

Hello Baoqua,

On Tue,  5 Aug 2025 14:23:33 +0800 Baoquan He <bhe@...hat.com> wrote:

> Now everything is ready, set kasan=off can disable kasan for all
> three modes.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  include/linux/kasan-enabled.h | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
> index 32f2d19f599f..b5857e15ef14 100644
> --- a/include/linux/kasan-enabled.h
> +++ b/include/linux/kasan-enabled.h
> @@ -8,30 +8,21 @@ extern bool kasan_arg_disabled;
>  
>  DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
>  
> -#ifdef CONFIG_KASAN_HW_TAGS
> -
>  static __always_inline bool kasan_enabled(void)
>  {
>  	return static_branch_likely(&kasan_flag_enabled);
>  }

I found mm-new build fails when CONFIG_KASAN is unset as below, and 'git
bisect' points this patch.

      LD      .tmp_vmlinux1
    ld: lib/stackdepot.o:(__jump_table+0x8): undefined reference to `kasan_flag_enabled'

Since kasna_flag_enabled is defined in mm/kasan/common.c, I confirmed diff like
below fixes this.  I think it may not be a correct fix though, since I didn't
read this patchset thoroughly.

diff --git a/include/linux/kasan-enabled.h b/include/linux/kasan-enabled.h
index b5857e15ef14..a53d112b1020 100644
--- a/include/linux/kasan-enabled.h
+++ b/include/linux/kasan-enabled.h
@@ -8,11 +8,22 @@ extern bool kasan_arg_disabled;
 
 DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
 
+#ifdef CONFIG_KASAN
+
 static __always_inline bool kasan_enabled(void)
 {
 	return static_branch_likely(&kasan_flag_enabled);
 }
 
+#else /* CONFIG_KASAN */
+
+static inline bool kasan_enabled(void)
+{
+	return false;
+}
+
+#endif
+
 #ifdef CONFIG_KASAN_HW_TAGS
 static inline bool kasan_hw_tags_enabled(void)
 {


[...]

Thanks,
SJ