[PATCH V2] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m

[PATCH V2] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m

[Huacai Chen]

After commit 84caf98838a3e5f4bdb34 ("mm: stop storing migration_ops in
page->mapping") we get such an error message if CONFIG_ZSMALLOC=m:

 WARNING: CPU: 3 PID: 42 at mm/migrate.c:142 isolate_movable_ops_page+0xa8/0x1c0
 CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
 pc 9000000000540bd8 ra 9000000000540b84 tp 9000000100420000 sp 9000000100423a60
 a0 9000000100193a80 a1 000000000000000c a2 000000000000001b a3 ffffffffffffffff
 a4 ffffffffffffffff a5 0000000000000267 a6 0000000000000000 a7 9000000100423ae0
 t0 00000000000000f1 t1 00000000000000f6 t2 0000000000000000 t3 0000000000000001
 t4 ffffff00010eb834 t5 0000000000000040 t6 900000010c89d380 t7 90000000023fcc70
 t8 0000000000000018 u0 0000000000000000 s9 ffffff00010eb800 s0 ffffff00010eb800
 s1 000000000000000c s2 0000000000043ae0 s3 0000800000000000 s4 900000000219cc40
 s5 0000000000000000 s6 ffffff00010eb800 s7 0000000000000001 s8 90000000025b4000
    ra: 9000000000540b84 isolate_movable_ops_page+0x54/0x1c0
   ERA: 9000000000540bd8 isolate_movable_ops_page+0xa8/0x1c0
  CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
  PRMD: 00000004 (PPLV0 +PIE -PWE)
  EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
  ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
 ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0)
  PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)
 CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
 Stack : 90000000021fd000 0000000000000000 9000000000247720 9000000100420000
         90000001004236a0 90000001004236a8 0000000000000000 90000001004237e8
         90000001004237e0 90000001004237e0 9000000100423550 0000000000000001
         0000000000000001 90000001004236a8 725a84864a19e2d9 90000000023fcc58
         9000000100420000 90000000024c6848 9000000002416848 0000000000000001
         0000000000000000 000000000000000a 0000000007fe0000 ffffff00010eb800
         0000000000000000 90000000021fd000 0000000000000000 900000000205cf30
         000000000000008e 0000000000000009 ffffff00010eb800 0000000000000001
         90000000025b4000 0000000000000000 900000000024773c 00007ffff103d748
         00000000000000b0 0000000000000004 0000000000000000 0000000000071c1d
         ...
 Call Trace:
 [<900000000024773c>] show_stack+0x5c/0x190
 [<90000000002415e0>] dump_stack_lvl+0x70/0x9c
 [<90000000004abe6c>] isolate_migratepages_block+0x3bc/0x16e0
 [<90000000004af408>] compact_zone+0x558/0x1000
 [<90000000004b0068>] compact_node+0xa8/0x1e0
 [<90000000004b0aa4>] kcompactd+0x394/0x410
 [<90000000002b3c98>] kthread+0x128/0x140
 [<9000000001779148>] ret_from_kernel_thread+0x28/0xc0
 [<9000000000245528>] ret_from_kernel_thread_asm+0x10/0x88

The reason is that defined(CONFIG_ZSMALLOC) evaluates to 1 only when
CONFIG_ZSMALLOC=y, we should use IS_ENABLED(CONFIG_ZSMALLOC) instead.
But when I use IS_ENABLED(CONFIG_ZSMALLOC), page_movable_ops() cannot
access zsmalloc_mops because zsmalloc_mops is in a module.

To solve this problem, we define a movable_ops[] array in mm/migrate.c,
initialise its elements at mm/balloon_compaction.c & mm/zsmalloc.c, and
let the page_movable_ops() function return elements from movable_ops[].

Fixes: 84caf98838a3e5f ("mm: stop storing migration_ops in page->mapping")
Acked-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
V2: Use EXPORT_SYMBOL_GPL_FOR_MODULES instead of EXPORT_SYMBOL and fix build.

 include/linux/migrate.h |  6 ++++++
 mm/balloon_compaction.c |  7 +++++++
 mm/migrate.c            | 16 ++++++++++------
 mm/zsmalloc.c           |  6 ++++++
 4 files changed, 29 insertions(+), 6 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index acadd41e0b5c..58fac171e4d5 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -57,6 +57,12 @@ struct movable_operations {
 	void (*putback_page)(struct page *);
 };
 
+#define MOVABLE_BALLOON		0
+#define MOVABLE_ZSMALLOC	1
+#define MOVABLE_MAX		2
+
+extern const struct movable_operations *movable_ops[MOVABLE_MAX];
+
 /* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
diff --git a/mm/balloon_compaction.c b/mm/balloon_compaction.c
index 2a4a649805c1..a1d2625b5c39 100644
--- a/mm/balloon_compaction.c
+++ b/mm/balloon_compaction.c
@@ -254,4 +254,11 @@ const struct movable_operations balloon_mops = {
 	.putback_page = balloon_page_putback,
 };
 
+static int __init balloon_init(void)
+{
+	movable_ops[MOVABLE_BALLOON] = &balloon_mops;
+	return 0;
+}
+core_initcall(balloon_init);
+
 #endif /* CONFIG_BALLOON_COMPACTION */
diff --git a/mm/migrate.c b/mm/migrate.c
index 425401b2d4e1..92918fab3e1a 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -53,6 +53,10 @@
 #include "internal.h"
 #include "swap.h"
 
+const struct movable_operations *movable_ops[MOVABLE_MAX];
+
+EXPORT_SYMBOL_GPL_FOR_MODULES(movable_ops);
+
 static const struct movable_operations *page_movable_ops(struct page *page)
 {
 	VM_WARN_ON_ONCE_PAGE(!page_has_movable_ops(page), page);
@@ -62,15 +66,15 @@ static const struct movable_operations *page_movable_ops(struct page *page)
 	 * it as movable, the page type must be sticky until the page gets freed
 	 * back to the buddy.
 	 */
-#ifdef CONFIG_BALLOON_COMPACTION
+#if IS_ENABLED(CONFIG_BALLOON_COMPACTION)
 	if (PageOffline(page))
 		/* Only balloon compaction sets PageOffline pages movable. */
-		return &balloon_mops;
-#endif /* CONFIG_BALLOON_COMPACTION */
-#if defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION)
+		return movable_ops[MOVABLE_BALLOON];
+#endif /* IS_ENABLED(CONFIG_BALLOON_COMPACTION) */
+#if IS_ENABLED(CONFIG_ZSMALLOC) && IS_ENABLED(CONFIG_COMPACTION)
 	if (PageZsmalloc(page))
-		return &zsmalloc_mops;
-#endif /* defined(CONFIG_ZSMALLOC) && defined(CONFIG_COMPACTION) */
+		return movable_ops[MOVABLE_ZSMALLOC];
+#endif /* IS_ENABLED(CONFIG_ZSMALLOC) && IS_ENABLED(CONFIG_COMPACTION) */
 	return NULL;
 }
 
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 2c5e56a65354..052fcc0d29e5 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -2246,6 +2246,9 @@ EXPORT_SYMBOL_GPL(zs_destroy_pool);
 
 static int __init zs_init(void)
 {
+#ifdef CONFIG_COMPACTION
+	movable_ops[MOVABLE_ZSMALLOC] = &zsmalloc_mops;
+#endif
 #ifdef CONFIG_ZPOOL
 	zpool_register_driver(&zs_zpool_driver);
 #endif
@@ -2255,6 +2258,9 @@ static int __init zs_init(void)
 
 static void __exit zs_exit(void)
 {
+#ifdef CONFIG_COMPACTION
+	movable_ops[MOVABLE_ZSMALLOC] = NULL;
+#endif
 #ifdef CONFIG_ZPOOL
 	zpool_unregister_driver(&zs_zpool_driver);
 #endif
-- 
2.47.3

Re: [PATCH V2] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m

[David Hildenbrand]

On 16.08.25 09:21, Huacai Chen wrote:
> After commit 84caf98838a3e5f4bdb34 ("mm: stop storing migration_ops in
> page->mapping") we get such an error message if CONFIG_ZSMALLOC=m:
> 
>   WARNING: CPU: 3 PID: 42 at mm/migrate.c:142 isolate_movable_ops_page+0xa8/0x1c0
>   CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
>   pc 9000000000540bd8 ra 9000000000540b84 tp 9000000100420000 sp 9000000100423a60
>   a0 9000000100193a80 a1 000000000000000c a2 000000000000001b a3 ffffffffffffffff
>   a4 ffffffffffffffff a5 0000000000000267 a6 0000000000000000 a7 9000000100423ae0
>   t0 00000000000000f1 t1 00000000000000f6 t2 0000000000000000 t3 0000000000000001
>   t4 ffffff00010eb834 t5 0000000000000040 t6 900000010c89d380 t7 90000000023fcc70
>   t8 0000000000000018 u0 0000000000000000 s9 ffffff00010eb800 s0 ffffff00010eb800
>   s1 000000000000000c s2 0000000000043ae0 s3 0000800000000000 s4 900000000219cc40
>   s5 0000000000000000 s6 ffffff00010eb800 s7 0000000000000001 s8 90000000025b4000
>      ra: 9000000000540b84 isolate_movable_ops_page+0x54/0x1c0
>     ERA: 9000000000540bd8 isolate_movable_ops_page+0xa8/0x1c0
>    CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
>    PRMD: 00000004 (PPLV0 +PIE -PWE)
>    EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
>    ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
>   ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0)
>    PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)
>   CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
>   Stack : 90000000021fd000 0000000000000000 9000000000247720 9000000100420000
>           90000001004236a0 90000001004236a8 0000000000000000 90000001004237e8
>           90000001004237e0 90000001004237e0 9000000100423550 0000000000000001
>           0000000000000001 90000001004236a8 725a84864a19e2d9 90000000023fcc58
>           9000000100420000 90000000024c6848 9000000002416848 0000000000000001
>           0000000000000000 000000000000000a 0000000007fe0000 ffffff00010eb800
>           0000000000000000 90000000021fd000 0000000000000000 900000000205cf30
>           000000000000008e 0000000000000009 ffffff00010eb800 0000000000000001
>           90000000025b4000 0000000000000000 900000000024773c 00007ffff103d748
>           00000000000000b0 0000000000000004 0000000000000000 0000000000071c1d
>           ...
>   Call Trace:
>   [<900000000024773c>] show_stack+0x5c/0x190
>   [<90000000002415e0>] dump_stack_lvl+0x70/0x9c
>   [<90000000004abe6c>] isolate_migratepages_block+0x3bc/0x16e0
>   [<90000000004af408>] compact_zone+0x558/0x1000
>   [<90000000004b0068>] compact_node+0xa8/0x1e0
>   [<90000000004b0aa4>] kcompactd+0x394/0x410
>   [<90000000002b3c98>] kthread+0x128/0x140
>   [<9000000001779148>] ret_from_kernel_thread+0x28/0xc0
>   [<9000000000245528>] ret_from_kernel_thread_asm+0x10/0x88
> 
> The reason is that defined(CONFIG_ZSMALLOC) evaluates to 1 only when
> CONFIG_ZSMALLOC=y, we should use IS_ENABLED(CONFIG_ZSMALLOC) instead.
> But when I use IS_ENABLED(CONFIG_ZSMALLOC), page_movable_ops() cannot
> access zsmalloc_mops because zsmalloc_mops is in a module.
> 
> To solve this problem, we define a movable_ops[] array in mm/migrate.c,
> initialise its elements at mm/balloon_compaction.c & mm/zsmalloc.c, and
> let the page_movable_ops() function return elements from movable_ops[].
> 
> Fixes: 84caf98838a3e5f ("mm: stop storing migration_ops in page->mapping")
> Acked-by: Zi Yan <ziy@nvidia.com>
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> ---
> V2: Use EXPORT_SYMBOL_GPL_FOR_MODULES instead of EXPORT_SYMBOL and fix build.

See my review.

Please wait longer for a resend, so we don't have to do this weird 
review dance.

-- 
Cheers

David / dhildenb

Re: [PATCH V2] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m

[Huacai Chen]

Hi, David,

On Sat, Aug 16, 2025 at 3:28 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 16.08.25 09:21, Huacai Chen wrote:
> > After commit 84caf98838a3e5f4bdb34 ("mm: stop storing migration_ops in
> > page->mapping") we get such an error message if CONFIG_ZSMALLOC=m:
> >
> >   WARNING: CPU: 3 PID: 42 at mm/migrate.c:142 isolate_movable_ops_page+0xa8/0x1c0
> >   CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
> >   pc 9000000000540bd8 ra 9000000000540b84 tp 9000000100420000 sp 9000000100423a60
> >   a0 9000000100193a80 a1 000000000000000c a2 000000000000001b a3 ffffffffffffffff
> >   a4 ffffffffffffffff a5 0000000000000267 a6 0000000000000000 a7 9000000100423ae0
> >   t0 00000000000000f1 t1 00000000000000f6 t2 0000000000000000 t3 0000000000000001
> >   t4 ffffff00010eb834 t5 0000000000000040 t6 900000010c89d380 t7 90000000023fcc70
> >   t8 0000000000000018 u0 0000000000000000 s9 ffffff00010eb800 s0 ffffff00010eb800
> >   s1 000000000000000c s2 0000000000043ae0 s3 0000800000000000 s4 900000000219cc40
> >   s5 0000000000000000 s6 ffffff00010eb800 s7 0000000000000001 s8 90000000025b4000
> >      ra: 9000000000540b84 isolate_movable_ops_page+0x54/0x1c0
> >     ERA: 9000000000540bd8 isolate_movable_ops_page+0xa8/0x1c0
> >    CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
> >    PRMD: 00000004 (PPLV0 +PIE -PWE)
> >    EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
> >    ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
> >   ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0)
> >    PRID: 0014c010 (Loongson-64bit, Loongson-3A5000)
> >   CPU: 3 UID: 0 PID: 42 Comm: kcompactd0 Not tainted 6.16.0-rc5+ #2133 PREEMPT
> >   Stack : 90000000021fd000 0000000000000000 9000000000247720 9000000100420000
> >           90000001004236a0 90000001004236a8 0000000000000000 90000001004237e8
> >           90000001004237e0 90000001004237e0 9000000100423550 0000000000000001
> >           0000000000000001 90000001004236a8 725a84864a19e2d9 90000000023fcc58
> >           9000000100420000 90000000024c6848 9000000002416848 0000000000000001
> >           0000000000000000 000000000000000a 0000000007fe0000 ffffff00010eb800
> >           0000000000000000 90000000021fd000 0000000000000000 900000000205cf30
> >           000000000000008e 0000000000000009 ffffff00010eb800 0000000000000001
> >           90000000025b4000 0000000000000000 900000000024773c 00007ffff103d748
> >           00000000000000b0 0000000000000004 0000000000000000 0000000000071c1d
> >           ...
> >   Call Trace:
> >   [<900000000024773c>] show_stack+0x5c/0x190
> >   [<90000000002415e0>] dump_stack_lvl+0x70/0x9c
> >   [<90000000004abe6c>] isolate_migratepages_block+0x3bc/0x16e0
> >   [<90000000004af408>] compact_zone+0x558/0x1000
> >   [<90000000004b0068>] compact_node+0xa8/0x1e0
> >   [<90000000004b0aa4>] kcompactd+0x394/0x410
> >   [<90000000002b3c98>] kthread+0x128/0x140
> >   [<9000000001779148>] ret_from_kernel_thread+0x28/0xc0
> >   [<9000000000245528>] ret_from_kernel_thread_asm+0x10/0x88
> >
> > The reason is that defined(CONFIG_ZSMALLOC) evaluates to 1 only when
> > CONFIG_ZSMALLOC=y, we should use IS_ENABLED(CONFIG_ZSMALLOC) instead.
> > But when I use IS_ENABLED(CONFIG_ZSMALLOC), page_movable_ops() cannot
> > access zsmalloc_mops because zsmalloc_mops is in a module.
> >
> > To solve this problem, we define a movable_ops[] array in mm/migrate.c,
> > initialise its elements at mm/balloon_compaction.c & mm/zsmalloc.c, and
> > let the page_movable_ops() function return elements from movable_ops[].
> >
> > Fixes: 84caf98838a3e5f ("mm: stop storing migration_ops in page->mapping")
> > Acked-by: Zi Yan <ziy@nvidia.com>
> > Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> > ---
> > V2: Use EXPORT_SYMBOL_GPL_FOR_MODULES instead of EXPORT_SYMBOL and fix build.
>
> See my review.
>
> Please wait longer for a resend, so we don't have to do this weird
> review dance.
I'm sorry, when I receive Zi Yan's Ack I think there is no big
problems, so I sent V2.

Huacai

>
> --
> Cheers
>
> David / dhildenb
>

Re: [PATCH V2] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m

[kernel test robot]

Hi Huacai,

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/Huacai-Chen/mm-migrate-Fix-NULL-movable_ops-if-CONFIG_ZSMALLOC-m/20250816-152326
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20250816072149.1952348-1-chenhuacai%40loongson.cn
patch subject: [PATCH V2] mm/migrate: Fix NULL movable_ops if CONFIG_ZSMALLOC=m
config: arm-randconfig-003-20250817 (https://download.01.org/0day-ci/archive/20250817/202508170118.0VFEAq7Q-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 93d24b6b7b148c47a2fa228a4ef31524fa1d9f3f)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250817/202508170118.0VFEAq7Q-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@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202508170118.0VFEAq7Q-lkp@intel.com/

All errors (new ones prefixed by >>):

>> mm/migrate.c:58:42: error: too few arguments provided to function-like macro invocation
      58 | EXPORT_SYMBOL_GPL_FOR_MODULES(movable_ops);
         |                                          ^
   include/linux/export.h:94:9: note: macro 'EXPORT_SYMBOL_GPL_FOR_MODULES' defined here
      94 | #define EXPORT_SYMBOL_GPL_FOR_MODULES(sym, mods) __EXPORT_SYMBOL(sym, "GPL", "module:" mods)
         |         ^
>> mm/migrate.c:58:1: error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]
      58 | EXPORT_SYMBOL_GPL_FOR_MODULES(movable_ops);
         | ^
         | int
   2 errors generated.


vim +58 mm/migrate.c

    57	
  > 58	EXPORT_SYMBOL_GPL_FOR_MODULES(movable_ops);
    59	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki