linux-kernel - Re: [PATCH 3/4] mm: prevent KSM from completely breaking VMA merging

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Message-ID: <0b84abb7-a6a6-454d-bd02-861c49840ff3@lucifer.local>
Date: Mon, 19 May 2025 14:36:51 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel test robot <lkp@...el.com>, llvm@...ts.linux.dev,
        oe-kbuild-all@...ts.linux.dev,
        Linux Memory Management List <linux-mm@...ck.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Pedro Falcato <pfalcato@...e.de>, David Hildenbrand <david@...hat.com>,
        Xu Xin <xu.xin16@....com.cn>,
        Chengming Zhou <chengming.zhou@...ux.dev>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 3/4] mm: prevent KSM from completely breaking VMA merging

Andrew - fix-patch enclosed for this. Silly oversight.

Will also fixup on any respin.

Thanks, Lorenzo

On Mon, May 19, 2025 at 09:19:50PM +0800, kernel test robot wrote:
> Hi Lorenzo,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on akpm-mm/mm-everything]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Lorenzo-Stoakes/mm-ksm-have-KSM-VMA-checks-not-require-a-VMA-pointer/20250519-165315
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link:    https://lore.kernel.org/r/418d3edbec3a718a7023f1beed5478f5952fc3df.1747431920.git.lorenzo.stoakes%40oracle.com
> patch subject: [PATCH 3/4] mm: prevent KSM from completely breaking VMA merging
> config: x86_64-buildonly-randconfig-001-20250519 (https://download.01.org/0day-ci/archive/20250519/202505192132.NsAm4haK-lkp@intel.com/config)
> compiler: clang version 20.1.2 (https://github.com/llvm/llvm-project 58df0ef89dd64126512e4ee27b4ac3fd8ddf6247)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250519/202505192132.NsAm4haK-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202505192132.NsAm4haK-lkp@intel.com/
>
> All errors (new ones prefixed by >>):
>
> >> mm/vma.c:2589:15: error: call to undeclared function 'ksm_vma_flags'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>     2589 |         map->flags = ksm_vma_flags(map->mm, map->file, map->flags);
>          |                      ^
>    mm/vma.c:2761:10: error: call to undeclared function 'ksm_vma_flags'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>     2761 |         flags = ksm_vma_flags(mm, NULL, flags);
>          |                 ^
>    2 errors generated.

Ugh ok looks like I forgot to provide an #else for the #ifdef CONFIG_KSM here.

>
>
> vim +/ksm_vma_flags +2589 mm/vma.c
>
>   2586
>   2587	static void update_ksm_flags(struct mmap_state *map)
>   2588	{
> > 2589		map->flags = ksm_vma_flags(map->mm, map->file, map->flags);
>   2590	}
>   2591
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki

----8<----
>From 2dbb9c4471f6145a513b5a2a661c78d3269fc9fe Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Date: Mon, 19 May 2025 14:36:14 +0100
Subject: [PATCH] fix

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
---
 include/linux/ksm.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/ksm.h b/include/linux/ksm.h
index ba5664daca6e..febc8acc565d 100644
--- a/include/linux/ksm.h
+++ b/include/linux/ksm.h
@@ -97,8 +97,11 @@ bool ksm_process_mergeable(struct mm_struct *mm);

 #else  /* !CONFIG_KSM */

-static inline void ksm_add_vma(struct vm_area_struct *vma)
+static inline vm_flags_t ksm_vma_flags(const struct mm_struct *mm,
+		const struct file *file,
+		vm_flags_t vm_flags)
 {
+	return vm_flags;
 }

 static inline int ksm_disable(struct mm_struct *mm)
--
2.49.0