On Mon 28-08-17 18:27:05, Stephen Rothwell wrote:

quoted

Hi Michal,

On Mon, 28 Aug 2017 09:59:31 +0200 Michal Hocko [off-list ref] wrote:

quoted

From 31d551dbcb1b7987a4cd07767c1e2805849b7a26 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Mon, 28 Aug 2017 09:41:39 +0200
Subject: [PATCH]
 mm-hmm-struct-hmm-is-only-use-by-hmm-mirror-functionality-v2-fix

Compiler is complaining for allnoconfig

kernel/fork.c: In function 'mm_init':
kernel/fork.c:814:2: error: implicit declaration of function
'hmm_mm_init' [-Werror=implicit-function-declaration]
  hmm_mm_init(mm);
  ^
kernel/fork.c: In function '__mmdrop':
kernel/fork.c:893:2: error: implicit declaration of function
'hmm_mm_destroy' [-Werror=implicit-function-declaration]
  hmm_mm_destroy(mm);

Make sure that hmm_mm_init/hmm_mm_destroy empty stups are defined when
CONFIG_HMM is disabled.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/hmm.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 9583d9a15f9c..aeb94e682dda 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h

@@ -508,11 +508,10 @@ static inline void hmm_mm_init(struct mm_struct

*mm)
 {
 	mm->hmm = NULL;
 }
-#else /* IS_ENABLED(CONFIG_HMM_MIRROR) */
+#endif
+
+#else /* IS_ENABLED(CONFIG_HMM) */
 static inline void hmm_mm_destroy(struct mm_struct *mm) {}
 static inline void hmm_mm_init(struct mm_struct *mm) {}
-#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
-
-
 #endif /* IS_ENABLED(CONFIG_HMM) */
 #endif /* LINUX_HMM_H */

What happens when CONFIG_HMM is defined but CONFIG_HMM_MIRROR is not?
Or is that not possible (in which case why would we have
CONFIG_HMM_MIRROR)?

This is something to Jerome to answer but hmm_mm_init/hmm_mm_destroy are
used regardless of the specific HMM configuration so an empty stub
should be defined unconditionally AFAIU.

Sorry for the build issue i posted a patch on friday that i tested against
all combination :

https://lkml.org/lkml/2017/8/25/802

Michal is right this function needs to be defined no matter what but they
only need to be stub if HMM_MIRROR is not enabled.

The fix i posted has the correct logic. I missplaced the endif when i was
fixing Arnd build issue when HMM_MIRROR was not enabled but other HMM feature
were.

Jérôme

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