[syzbot] [mm?] WARNING in move_to_new_folio

[syzbot] [mm?] WARNING in move_to_new_folio

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    01c6df60d5d4 Add linux-next specific files for 20250411
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=107b77e4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/928246b3f3d5/disk-01c6df60.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/79a68c4e1134/vmlinux-01c6df60.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9caf8c293819/bzImage-01c6df60.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com

------------[ cut here ]------------
jfs_metapage_aops does not implement migrate_folio
WARNING: CPU: 0 PID: 6870 at mm/migrate.c:955 fallback_migrate_folio mm/migrate.c:953 [inline]
WARNING: CPU: 0 PID: 6870 at mm/migrate.c:955 move_to_new_folio+0x70e/0x840 mm/migrate.c:1007
Modules linked in:
CPU: 0 UID: 0 PID: 6870 Comm: syz.3.196 Not tainted 6.15.0-rc1-next-20250411-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
RIP: 0010:fallback_migrate_folio mm/migrate.c:953 [inline]
RIP: 0010:move_to_new_folio+0x70e/0x840 mm/migrate.c:1007
Code: b8 00 00 00 00 00 fc ff df 41 80 7c 05 00 00 74 08 4c 89 e7 e8 73 2d fe ff 49 8b 34 24 48 c7 c7 00 8b 57 8c e8 d3 0b 53 ff 90 <0f> 0b 90 90 e9 0a fd ff ff e8 74 f6 93 ff 90 0f 0b 90 eb a7 e8 69
RSP: 0018:ffffc900045aeb30 EFLAGS: 00010246
RAX: d74fd979f2566d00 RBX: 0000000000000000 RCX: 0000000000080000
RDX: ffffc9000e489000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: ffffea0000c98800 R08: ffffffff81829232 R09: 1ffff110170c4852
R10: dffffc0000000000 R11: ffffed10170c4853 R12: ffff8880612710a8
R13: 1ffff1100c24e215 R14: ffffffff8c839248 R15: ffff888061270f88
FS:  00007f855ea5e6c0(0000) GS:ffff888124f80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000008 CR3: 000000003477c000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 migrate_folio_move mm/migrate.c:1312 [inline]
 migrate_folios_move mm/migrate.c:1664 [inline]
 migrate_pages_batch+0x1e86/0x30b0 mm/migrate.c:1911
 migrate_pages_sync mm/migrate.c:1968 [inline]
 migrate_pages+0x24f8/0x3470 mm/migrate.c:2050
 compact_zone+0x365d/0x4dd0 mm/compaction.c:2689
 compact_node mm/compaction.c:2958 [inline]
 compact_nodes mm/compaction.c:2980 [inline]
 sysctl_compaction_handler+0x498/0x9a0 mm/compaction.c:3031
 proc_sys_call_handler+0x54b/0x820 fs/proc/proc_sysctl.c:601
 iter_file_splice_write+0xbdf/0x1530 fs/splice.c:738
 do_splice_from fs/splice.c:935 [inline]
 direct_splice_actor+0x11b/0x220 fs/splice.c:1158
 splice_direct_to_actor+0x595/0xc90 fs/splice.c:1102
 do_splice_direct_actor fs/splice.c:1201 [inline]
 do_splice_direct+0x281/0x3d0 fs/splice.c:1227
 do_sendfile+0x582/0x8d0 fs/read_write.c:1368
 __do_sys_sendfile64 fs/read_write.c:1423 [inline]
 __se_sys_sendfile64+0x102/0x1e0 fs/read_write.c:1415
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f855db8d169
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f855ea5e038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f855dda6080 RCX: 00007f855db8d169
RDX: 00002000000000c0 RSI: 0000000000000006 RDI: 0000000000000007
RBP: 00007f855dc0e990 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000009 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f855dda6080 R15: 00007ffe70b954f8
 </TASK>


---
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If you want to undo deduplication, reply with:
#syz undup

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    01c6df60d5d4 Add linux-next specific files for 20250411
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=111db870580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10afca3f980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=116f5c04580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/928246b3f3d5/disk-01c6df60.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/79a68c4e1134/vmlinux-01c6df60.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9caf8c293819/bzImage-01c6df60.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/9e5bb76a4272/mount_3.gz
  fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=14ebd398580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com

------------[ cut here ]------------
jfs_metapage_aops does not implement migrate_folio
WARNING: CPU: 1 PID: 5861 at mm/migrate.c:955 fallback_migrate_folio mm/migrate.c:953 [inline]
WARNING: CPU: 1 PID: 5861 at mm/migrate.c:955 move_to_new_folio+0x70e/0x840 mm/migrate.c:1007
Modules linked in:
CPU: 1 UID: 0 PID: 5861 Comm: syz-executor280 Not tainted 6.15.0-rc1-next-20250411-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
RIP: 0010:fallback_migrate_folio mm/migrate.c:953 [inline]
RIP: 0010:move_to_new_folio+0x70e/0x840 mm/migrate.c:1007
Code: b8 00 00 00 00 00 fc ff df 41 80 7c 05 00 00 74 08 4c 89 e7 e8 73 2d fe ff 49 8b 34 24 48 c7 c7 00 8b 57 8c e8 d3 0b 53 ff 90 <0f> 0b 90 90 e9 0a fd ff ff e8 74 f6 93 ff 90 0f 0b 90 eb a7 e8 69
RSP: 0018:ffffc90003f16b30 EFLAGS: 00010246
RAX: b07441ff5c2b4f00 RBX: 0000000000000000 RCX: ffff88803508bc00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffea00008cc8c0 R08: ffffffff81829232 R09: fffffbfff1d7ab08
R10: dffffc0000000000 R11: fffffbfff1d7ab08 R12: ffff888075b9d130
R13: 1ffff1100eb73a26 R14: ffffffff8c839248 R15: ffff888075b9d010
FS:  0000555581ea4380(0000) GS:ffff888125080000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb8bd341e36 CR3: 000000003002a000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 migrate_folio_move mm/migrate.c:1312 [inline]
 migrate_folios_move mm/migrate.c:1664 [inline]
 migrate_pages_batch+0x1e86/0x30b0 mm/migrate.c:1911
 migrate_pages_sync mm/migrate.c:1941 [inline]
 migrate_pages+0x1e13/0x3470 mm/migrate.c:2050
 compact_zone+0x365d/0x4dd0 mm/compaction.c:2689
 compact_node mm/compaction.c:2958 [inline]
 compact_nodes mm/compaction.c:2980 [inline]
 sysctl_compaction_handler+0x498/0x9a0 mm/compaction.c:3031
 proc_sys_call_handler+0x54b/0x820 fs/proc/proc_sysctl.c:601
 iter_file_splice_write+0xbdf/0x1530 fs/splice.c:738
 do_splice_from fs/splice.c:935 [inline]
 direct_splice_actor+0x11b/0x220 fs/splice.c:1158
 splice_direct_to_actor+0x595/0xc90 fs/splice.c:1102
 do_splice_direct_actor fs/splice.c:1201 [inline]
 do_splice_direct+0x281/0x3d0 fs/splice.c:1227
 do_sendfile+0x582/0x8d0 fs/read_write.c:1368
 __do_sys_sendfile64 fs/read_write.c:1423 [inline]
 __se_sys_sendfile64+0x102/0x1e0 fs/read_write.c:1415
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0011f6cc49
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeb8797248 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f0011f6cc49
RDX: 0000200000000180 RSI: 0000000000000003 RDI: 0000000000000004
RBP: 00000000000f4240 R08: 0000555581ea5378 R09: 0000555581ea5378
R10: 000000000000000a R11: 0000000000000246 R12: 00000000000161d0
R13: 00007ffeb8797280 R14: 00007ffeb879726c R15: 00007f0011fb503b
 </TASK>


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[syzbot]

syzbot has bisected this issue to:

commit 7ee3647243e5c4a9d74d4c7ec621eac75c6d37ea
Author: Matthew Wilcox (Oracle) <willy@infradead.org>
Date:   Wed Apr 2 14:59:57 2025 +0000

    migrate: Remove call to ->writepage

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15be8fe4580000
start commit:   01c6df60d5d4 Add linux-next specific files for 20250411
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=17be8fe4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=13be8fe4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10afca3f980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=116f5c04580000

Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com
Fixes: 7ee3647243e5 ("migrate: Remove call to ->writepage")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] Re: [syzbot] [mm?] WARNING in move_to_new_folio

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Re: [syzbot] [mm?] WARNING in move_to_new_folio
Author: shivankg@amd.com

On 4/14/2025 3:14 AM, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 7ee3647243e5c4a9d74d4c7ec621eac75c6d37ea
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> Date:   Wed Apr 2 14:59:57 2025 +0000
> 
>     migrate: Remove call to ->writepage
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15be8fe4580000
> start commit:   01c6df60d5d4 Add linux-next specific files for 20250411
> git tree:       linux-next
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=17be8fe4580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=13be8fe4580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
> dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10afca3f980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=116f5c04580000
> 
> Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com
> Fixes: 7ee3647243e5 ("migrate: Remove call to ->writepage")
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

#syz test

diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index df575a873ec6..50759a846e22 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -15,6 +15,7 @@
 #include <linux/mempool.h>
 #include <linux/seq_file.h>
 #include <linux/writeback.h>
+#include <linux/migrate.h>
 #include "jfs_incore.h"
 #include "jfs_superblock.h"
 #include "jfs_filsys.h"
@@ -151,6 +152,54 @@ static inline void dec_io(struct folio *folio, blk_status_t status,
 		handler(folio, anchor->status);
 }
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct meta_anchor *src_anchor = src->private;
+	struct metapage *mps[MPS_PER_PAGE] = {0};
+	struct metapage *mp;
+	int i, rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (mp && metapage_locked(mp))
+			return -EAGAIN;
+	}
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (!mp)
+			continue;
+		if (unlikely(insert_metapage(dst, mp))) {
+			/* If error, roll-back previosly inserted pages */
+			for (int j = 0 ; j < i; j++) {
+				if (mps[j])
+					remove_metapage(dst, mps[j]);
+			}
+			return -EAGAIN;
+		}
+		mps[i] = mp;
+	}
+
+	/* Update the metapage and remove it from src */
+	for (int i = 0; i < MPS_PER_PAGE; i++) {
+		mp = mps[i];
+		if (mp) {
+			int page_offset = mp->data - folio_address(src);
+
+			mp->data = folio_address(dst) + page_offset;
+			mp->folio = dst;
+			remove_metapage(src, mp);
+		}
+	}
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #else
 static inline struct metapage *folio_to_mp(struct folio *folio, int offset)
 {
@@ -175,6 +224,32 @@ static inline void remove_metapage(struct folio *folio, struct metapage *mp)
 #define inc_io(folio) do {} while(0)
 #define dec_io(folio, status, handler) handler(folio, status)
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct metapage *mp;
+	int page_offset;
+	int rc;
+
+	mp = folio_to_mp(src, 0);
+	if (mp && metapage_locked(mp))
+		return -EAGAIN;
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	if (unlikely(insert_metapage(src, mp)))
+		return -EAGAIN;
+
+	page_offset = mp->data - folio_address(src);
+	mp->data = folio_address(dst) + page_offset;
+	mp->folio = dst;
+	remove_metapage(src, mp);
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #endif
 
 static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
@@ -554,6 +629,24 @@ static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)
 	return ret;
 }
 
+/**
+ * metapage_migrate_folio - Migration function for JFS metapages
+ */
+static int metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				  struct folio *src, enum migrate_mode mode)
+{
+	int expected_count;
+
+	if (!src->private)
+		return filemap_migrate_folio(mapping, dst, src, mode);
+
+	/* Check whether page does not have extra refs before we do more work */
+	expected_count = folio_expected_refs(mapping, src);
+	if (folio_ref_count(src) != expected_count)
+		return -EAGAIN;
+	return __metapage_migrate_folio(mapping, dst, src, mode);
+}
+
 static void metapage_invalidate_folio(struct folio *folio, size_t offset,
 				    size_t length)
 {
@@ -570,6 +663,7 @@ const struct address_space_operations jfs_metapage_aops = {
 	.release_folio	= metapage_release_folio,
 	.invalidate_folio = metapage_invalidate_folio,
 	.dirty_folio	= filemap_dirty_folio,
+	.migrate_folio	= metapage_migrate_folio,
 };
 
 struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index aaa2114498d6..cb31c5b1eb6a 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -60,6 +60,7 @@ struct movable_operations {
 /* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
+int folio_expected_refs(struct address_space *mapping, struct folio *folio);
 #ifdef CONFIG_MIGRATION
 
 void putback_movable_pages(struct list_head *l);
diff --git a/mm/migrate.c b/mm/migrate.c
index 6e2488e5dbe4..0f01b8a87dec 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -445,7 +445,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 }
 #endif
 
-static int folio_expected_refs(struct address_space *mapping,
+int folio_expected_refs(struct address_space *mapping,
 		struct folio *folio)
 {
 	int refs = 1;
@@ -458,6 +458,7 @@ static int folio_expected_refs(struct address_space *mapping,
 
 	return refs;
 }
+EXPORT_SYMBOL_GPL(folio_expected_refs);
 
 /*
  * Replace the folio in the mapping.
-- 
2.34.1

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[Shivank Garg]

[-- Attachment #1: Type: text/plain, Size: 1243 bytes --]


#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 01c6df60d5d4

Best Regards,
Shivank

On 4/14/2025 3:14 AM, syzbot wrote:
> syzbot has bisected this issue to:
> 
> commit 7ee3647243e5c4a9d74d4c7ec621eac75c6d37ea
> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
> Date:   Wed Apr 2 14:59:57 2025 +0000
> 
>     migrate: Remove call to ->writepage
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=15be8fe4580000
> start commit:   01c6df60d5d4 Add linux-next specific files for 20250411
> git tree:       linux-next
> final oops:     https://syzkaller.appspot.com/x/report.txt?x=17be8fe4580000
> console output: https://syzkaller.appspot.com/x/log.txt?x=13be8fe4580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
> dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10afca3f980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=116f5c04580000
> 
> Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com
> Fixes: 7ee3647243e5 ("migrate: Remove call to ->writepage")
> 
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[-- Attachment #2: 0001-jfs-implement-migrate_folio-for-jfs_metapage_aops.patch --]
[-- Type: text/plain, Size: 6141 bytes --]

From 0cd57d102a07f453d4a722215ce8ae34ff81c0a1 Mon Sep 17 00:00:00 2001
From: Shivank Garg <shivankg@amd.com>
Date: Sun, 13 Apr 2025 16:40:53 +0000
Subject: [PATCH] jfs: implement migrate_folio for jfs_metapage_aops

Add the missing migrate_folio operation to jfs_metapage_aops to fix
warnings during memory compaction. These warnings were introduced by
commit 7ee3647243e5 ("migrate: Remove call to ->writepage") which
added explicit warnings when filesystems don't implement migrate_folio.

System reports following warnings:
  jfs_metapage_aops does not implement migrate_folio
  WARNING: CPU: 0 PID: 6870 at mm/migrate.c:955 fallback_migrate_folio mm/migrate.c:953 [inline]
  WARNING: CPU: 0 PID: 6870 at mm/migrate.c:955 move_to_new_folio+0x70e/0x840 mm/migrate.c:1007

Implement metapage_migrate_folio which handles both single and multiple
metapages per page configurations.

Fixes: 35474d52c605 ("jfs: Convert metapage_writepage to metapage_write_folio")
Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67faff52.050a0220.379d84.001b.GAE@google.com
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 fs/jfs/jfs_metapage.c   | 94 +++++++++++++++++++++++++++++++++++++++++
 include/linux/migrate.h |  1 +
 mm/migrate.c            |  3 +-
 3 files changed, 97 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index df575a873ec6..50759a846e22 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -15,6 +15,7 @@
 #include <linux/mempool.h>
 #include <linux/seq_file.h>
 #include <linux/writeback.h>
+#include <linux/migrate.h>
 #include "jfs_incore.h"
 #include "jfs_superblock.h"
 #include "jfs_filsys.h"
@@ -151,6 +152,54 @@ static inline void dec_io(struct folio *folio, blk_status_t status,
 		handler(folio, anchor->status);
 }
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct meta_anchor *src_anchor = src->private;
+	struct metapage *mps[MPS_PER_PAGE] = {0};
+	struct metapage *mp;
+	int i, rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (mp && metapage_locked(mp))
+			return -EAGAIN;
+	}
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (!mp)
+			continue;
+		if (unlikely(insert_metapage(dst, mp))) {
+			/* If error, roll-back previosly inserted pages */
+			for (int j = 0 ; j < i; j++) {
+				if (mps[j])
+					remove_metapage(dst, mps[j]);
+			}
+			return -EAGAIN;
+		}
+		mps[i] = mp;
+	}
+
+	/* Update the metapage and remove it from src */
+	for (int i = 0; i < MPS_PER_PAGE; i++) {
+		mp = mps[i];
+		if (mp) {
+			int page_offset = mp->data - folio_address(src);
+
+			mp->data = folio_address(dst) + page_offset;
+			mp->folio = dst;
+			remove_metapage(src, mp);
+		}
+	}
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #else
 static inline struct metapage *folio_to_mp(struct folio *folio, int offset)
 {
@@ -175,6 +224,32 @@ static inline void remove_metapage(struct folio *folio, struct metapage *mp)
 #define inc_io(folio) do {} while(0)
 #define dec_io(folio, status, handler) handler(folio, status)
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct metapage *mp;
+	int page_offset;
+	int rc;
+
+	mp = folio_to_mp(src, 0);
+	if (mp && metapage_locked(mp))
+		return -EAGAIN;
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	if (unlikely(insert_metapage(src, mp)))
+		return -EAGAIN;
+
+	page_offset = mp->data - folio_address(src);
+	mp->data = folio_address(dst) + page_offset;
+	mp->folio = dst;
+	remove_metapage(src, mp);
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #endif
 
 static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
@@ -554,6 +629,24 @@ static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)
 	return ret;
 }
 
+/**
+ * metapage_migrate_folio - Migration function for JFS metapages
+ */
+static int metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				  struct folio *src, enum migrate_mode mode)
+{
+	int expected_count;
+
+	if (!src->private)
+		return filemap_migrate_folio(mapping, dst, src, mode);
+
+	/* Check whether page does not have extra refs before we do more work */
+	expected_count = folio_expected_refs(mapping, src);
+	if (folio_ref_count(src) != expected_count)
+		return -EAGAIN;
+	return __metapage_migrate_folio(mapping, dst, src, mode);
+}
+
 static void metapage_invalidate_folio(struct folio *folio, size_t offset,
 				    size_t length)
 {
@@ -570,6 +663,7 @@ const struct address_space_operations jfs_metapage_aops = {
 	.release_folio	= metapage_release_folio,
 	.invalidate_folio = metapage_invalidate_folio,
 	.dirty_folio	= filemap_dirty_folio,
+	.migrate_folio	= metapage_migrate_folio,
 };
 
 struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index aaa2114498d6..cb31c5b1eb6a 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -60,6 +60,7 @@ struct movable_operations {
 /* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
+int folio_expected_refs(struct address_space *mapping, struct folio *folio);
 #ifdef CONFIG_MIGRATION
 
 void putback_movable_pages(struct list_head *l);
diff --git a/mm/migrate.c b/mm/migrate.c
index 6e2488e5dbe4..0f01b8a87dec 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -445,7 +445,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 }
 #endif
 
-static int folio_expected_refs(struct address_space *mapping,
+int folio_expected_refs(struct address_space *mapping,
 		struct folio *folio)
 {
 	int refs = 1;
@@ -458,6 +458,7 @@ static int folio_expected_refs(struct address_space *mapping,
 
 	return refs;
 }
+EXPORT_SYMBOL_GPL(folio_expected_refs);
 
 /*
  * Replace the folio in the mapping.
-- 
2.34.1

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
unregister_netdevice: waiting for DEV to become free

unregister_netdevice: waiting for batadv0 to become free. Usage count = 3


Tested on:

commit:         01c6df60 Add linux-next specific files for 20250411
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=1142f0cc580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=107a60cc580000

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[Shivank Garg]

[-- Attachment #1: Type: text/plain, Size: 1072 bytes --]

I made a mistake in insert_metapage. I hope my revised patch work.
I'll post it to original list if this pass.

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 01c6df60d5d4

Best Regards,
Shivank

On 4/15/2025 10:54 AM, syzbot wrote:
> Hello,
> 
> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> unregister_netdevice: waiting for DEV to become free
> 
> unregister_netdevice: waiting for batadv0 to become free. Usage count = 3
> 
> 
> Tested on:
> 
> commit:         01c6df60 Add linux-next specific files for 20250411
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
> console output: https://syzkaller.appspot.com/x/log.txt?x=1142f0cc580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
> dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> patch:          https://syzkaller.appspot.com/x/patch.diff?x=107a60cc580000
> 



[-- Attachment #2: 0001-jfs-implement-migrate_folio-for-jfs_metapage_aops.patch --]
[-- Type: text/plain, Size: 6141 bytes --]

From daa1334f94c94b52117835dcd2d10ee319617458 Mon Sep 17 00:00:00 2001
From: Shivank Garg <shivankg@amd.com>
Date: Sun, 13 Apr 2025 16:40:53 +0000
Subject: [PATCH] jfs: implement migrate_folio for jfs_metapage_aops

Add the missing migrate_folio operation to jfs_metapage_aops to fix
warnings during memory compaction. These warnings were introduced by
commit 7ee3647243e5 ("migrate: Remove call to ->writepage") which
added explicit warnings when filesystems don't implement migrate_folio.

System reports following warnings:
  jfs_metapage_aops does not implement migrate_folio
  WARNING: CPU: 0 PID: 6870 at mm/migrate.c:955 fallback_migrate_folio mm/migrate.c:953 [inline]
  WARNING: CPU: 0 PID: 6870 at mm/migrate.c:955 move_to_new_folio+0x70e/0x840 mm/migrate.c:1007

Implement metapage_migrate_folio which handles both single and multiple
metapages per page configurations.

Fixes: 35474d52c605 ("jfs: Convert metapage_writepage to metapage_write_folio")
Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67faff52.050a0220.379d84.001b.GAE@google.com
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 fs/jfs/jfs_metapage.c   | 94 +++++++++++++++++++++++++++++++++++++++++
 include/linux/migrate.h |  1 +
 mm/migrate.c            |  3 +-
 3 files changed, 97 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index df575a873ec6..d440537db6fe 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -15,6 +15,7 @@
 #include <linux/mempool.h>
 #include <linux/seq_file.h>
 #include <linux/writeback.h>
+#include <linux/migrate.h>
 #include "jfs_incore.h"
 #include "jfs_superblock.h"
 #include "jfs_filsys.h"
@@ -151,6 +152,54 @@ static inline void dec_io(struct folio *folio, blk_status_t status,
 		handler(folio, anchor->status);
 }
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct meta_anchor *src_anchor = src->private;
+	struct metapage *mps[MPS_PER_PAGE] = {0};
+	struct metapage *mp;
+	int i, rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (mp && metapage_locked(mp))
+			return -EAGAIN;
+	}
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (!mp)
+			continue;
+		if (unlikely(insert_metapage(dst, mp))) {
+			/* If error, roll-back previosly inserted pages */
+			for (int j = 0 ; j < i; j++) {
+				if (mps[j])
+					remove_metapage(dst, mps[j]);
+			}
+			return -EAGAIN;
+		}
+		mps[i] = mp;
+	}
+
+	/* Update the metapage and remove it from src */
+	for (int i = 0; i < MPS_PER_PAGE; i++) {
+		mp = mps[i];
+		if (mp) {
+			int page_offset = mp->data - folio_address(src);
+
+			mp->data = folio_address(dst) + page_offset;
+			mp->folio = dst;
+			remove_metapage(src, mp);
+		}
+	}
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #else
 static inline struct metapage *folio_to_mp(struct folio *folio, int offset)
 {
@@ -175,6 +224,32 @@ static inline void remove_metapage(struct folio *folio, struct metapage *mp)
 #define inc_io(folio) do {} while(0)
 #define dec_io(folio, status, handler) handler(folio, status)
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct metapage *mp;
+	int page_offset;
+	int rc;
+
+	mp = folio_to_mp(src, 0);
+	if (mp && metapage_locked(mp))
+		return -EAGAIN;
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	if (unlikely(insert_metapage(dst, mp)))
+		return -EAGAIN;
+
+	page_offset = mp->data - folio_address(src);
+	mp->data = folio_address(dst) + page_offset;
+	mp->folio = dst;
+	remove_metapage(src, mp);
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #endif
 
 static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
@@ -554,6 +629,24 @@ static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)
 	return ret;
 }
 
+/**
+ * metapage_migrate_folio - Migration function for JFS metapages
+ */
+static int metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				  struct folio *src, enum migrate_mode mode)
+{
+	int expected_count;
+
+	if (!src->private)
+		return filemap_migrate_folio(mapping, dst, src, mode);
+
+	/* Check whether page does not have extra refs before we do more work */
+	expected_count = folio_expected_refs(mapping, src);
+	if (folio_ref_count(src) != expected_count)
+		return -EAGAIN;
+	return __metapage_migrate_folio(mapping, dst, src, mode);
+}
+
 static void metapage_invalidate_folio(struct folio *folio, size_t offset,
 				    size_t length)
 {
@@ -570,6 +663,7 @@ const struct address_space_operations jfs_metapage_aops = {
 	.release_folio	= metapage_release_folio,
 	.invalidate_folio = metapage_invalidate_folio,
 	.dirty_folio	= filemap_dirty_folio,
+	.migrate_folio	= metapage_migrate_folio,
 };
 
 struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index aaa2114498d6..cb31c5b1eb6a 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -60,6 +60,7 @@ struct movable_operations {
 /* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
+int folio_expected_refs(struct address_space *mapping, struct folio *folio);
 #ifdef CONFIG_MIGRATION
 
 void putback_movable_pages(struct list_head *l);
diff --git a/mm/migrate.c b/mm/migrate.c
index 6e2488e5dbe4..0f01b8a87dec 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -445,7 +445,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 }
 #endif
 
-static int folio_expected_refs(struct address_space *mapping,
+int folio_expected_refs(struct address_space *mapping,
 		struct folio *folio)
 {
 	int refs = 1;
@@ -458,6 +458,7 @@ static int folio_expected_refs(struct address_space *mapping,
 
 	return refs;
 }
+EXPORT_SYMBOL_GPL(folio_expected_refs);
 
 /*
  * Replace the folio in the mapping.
-- 
2.34.1

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
unregister_netdevice: waiting for DEV to become free

unregister_netdevice: waiting for batadv0 to become free. Usage count = 3


Tested on:

commit:         01c6df60 Add linux-next specific files for 20250411
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=13f1f398580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=12c3cfe4580000

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[Shivank Garg]

[-- Attachment #1: Type: text/plain, Size: 1474 bytes --]



On 4/15/2025 11:10 AM, Shivank Garg wrote:
> I made a mistake in insert_metapage. I hope my revised patch work.
> I'll post it to original list if this pass.
> 
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 01c6df60d5d4
> 
> Best Regards,
> Shivank
> 
> On 4/15/2025 10:54 AM, syzbot wrote:
>> Hello,
>>
>> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
>> unregister_netdevice: waiting for DEV to become free
>>
>> unregister_netdevice: waiting for batadv0 to become free. Usage count = 3
>>
>>
>> Tested on:
>>
>> commit:         01c6df60 Add linux-next specific files for 20250411
>> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
>> console output: https://syzkaller.appspot.com/x/log.txt?x=1142f0cc580000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
>> dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
>> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>> patch:          https://syzkaller.appspot.com/x/patch.diff?x=107a60cc580000
>>
> 
> 

Looks like this error is unrelated and due to a different issue:
https://lore.kernel.org/lkml/20250414-double_hold_fix-v5-1-10e056324cde@narfation.org

Retesting with Sven Eckelmann's patch for batman-adv

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 01c6df60d5d4

Best Regards,
Shivank




[-- Attachment #2: revised-diff --]
[-- Type: text/plain, Size: 5292 bytes --]

diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index df575a873ec6..d440537db6fe 100644
--- a/fs/jfs/jfs_metapage.c
+++ b/fs/jfs/jfs_metapage.c
@@ -15,6 +15,7 @@
 #include <linux/mempool.h>
 #include <linux/seq_file.h>
 #include <linux/writeback.h>
+#include <linux/migrate.h>
 #include "jfs_incore.h"
 #include "jfs_superblock.h"
 #include "jfs_filsys.h"
@@ -151,6 +152,54 @@ static inline void dec_io(struct folio *folio, blk_status_t status,
 		handler(folio, anchor->status);
 }
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct meta_anchor *src_anchor = src->private;
+	struct metapage *mps[MPS_PER_PAGE] = {0};
+	struct metapage *mp;
+	int i, rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (mp && metapage_locked(mp))
+			return -EAGAIN;
+	}
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	for (i = 0; i < MPS_PER_PAGE; i++) {
+		mp = src_anchor->mp[i];
+		if (!mp)
+			continue;
+		if (unlikely(insert_metapage(dst, mp))) {
+			/* If error, roll-back previosly inserted pages */
+			for (int j = 0 ; j < i; j++) {
+				if (mps[j])
+					remove_metapage(dst, mps[j]);
+			}
+			return -EAGAIN;
+		}
+		mps[i] = mp;
+	}
+
+	/* Update the metapage and remove it from src */
+	for (int i = 0; i < MPS_PER_PAGE; i++) {
+		mp = mps[i];
+		if (mp) {
+			int page_offset = mp->data - folio_address(src);
+
+			mp->data = folio_address(dst) + page_offset;
+			mp->folio = dst;
+			remove_metapage(src, mp);
+		}
+	}
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #else
 static inline struct metapage *folio_to_mp(struct folio *folio, int offset)
 {
@@ -175,6 +224,32 @@ static inline void remove_metapage(struct folio *folio, struct metapage *mp)
 #define inc_io(folio) do {} while(0)
 #define dec_io(folio, status, handler) handler(folio, status)
 
+static int __metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				    struct folio *src, enum migrate_mode mode)
+{
+	struct metapage *mp;
+	int page_offset;
+	int rc;
+
+	mp = folio_to_mp(src, 0);
+	if (mp && metapage_locked(mp))
+		return -EAGAIN;
+
+	rc = filemap_migrate_folio(mapping, dst, src, mode);
+	if (rc != MIGRATEPAGE_SUCCESS)
+		return rc;
+
+	if (unlikely(insert_metapage(dst, mp)))
+		return -EAGAIN;
+
+	page_offset = mp->data - folio_address(src);
+	mp->data = folio_address(dst) + page_offset;
+	mp->folio = dst;
+	remove_metapage(src, mp);
+
+	return MIGRATEPAGE_SUCCESS;
+}
+
 #endif
 
 static inline struct metapage *alloc_metapage(gfp_t gfp_mask)
@@ -554,6 +629,24 @@ static bool metapage_release_folio(struct folio *folio, gfp_t gfp_mask)
 	return ret;
 }
 
+/**
+ * metapage_migrate_folio - Migration function for JFS metapages
+ */
+static int metapage_migrate_folio(struct address_space *mapping, struct folio *dst,
+				  struct folio *src, enum migrate_mode mode)
+{
+	int expected_count;
+
+	if (!src->private)
+		return filemap_migrate_folio(mapping, dst, src, mode);
+
+	/* Check whether page does not have extra refs before we do more work */
+	expected_count = folio_expected_refs(mapping, src);
+	if (folio_ref_count(src) != expected_count)
+		return -EAGAIN;
+	return __metapage_migrate_folio(mapping, dst, src, mode);
+}
+
 static void metapage_invalidate_folio(struct folio *folio, size_t offset,
 				    size_t length)
 {
@@ -570,6 +663,7 @@ const struct address_space_operations jfs_metapage_aops = {
 	.release_folio	= metapage_release_folio,
 	.invalidate_folio = metapage_invalidate_folio,
 	.dirty_folio	= filemap_dirty_folio,
+	.migrate_folio	= metapage_migrate_folio,
 };
 
 struct metapage *__get_metapage(struct inode *inode, unsigned long lblock,
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index aaa2114498d6..cb31c5b1eb6a 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -60,6 +60,7 @@ struct movable_operations {
 /* Defined in mm/debug.c: */
 extern const char *migrate_reason_names[MR_TYPES];
 
+int folio_expected_refs(struct address_space *mapping, struct folio *folio);
 #ifdef CONFIG_MIGRATION
 
 void putback_movable_pages(struct list_head *l);
diff --git a/mm/migrate.c b/mm/migrate.c
index 6e2488e5dbe4..0f01b8a87dec 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -445,7 +445,7 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 }
 #endif
 
-static int folio_expected_refs(struct address_space *mapping,
+int folio_expected_refs(struct address_space *mapping,
 		struct folio *folio)
 {
 	int refs = 1;
@@ -458,6 +458,7 @@ static int folio_expected_refs(struct address_space *mapping,
 
 	return refs;
 }
+EXPORT_SYMBOL_GPL(folio_expected_refs);
 
 /*
  * Replace the folio in the mapping.
diff --git a/net/batman-adv/hard-interface.c b/net/batman-adv/hard-interface.c
index f145f9662653..7cd4bdcee439 100644
--- a/net/batman-adv/hard-interface.c
+++ b/net/batman-adv/hard-interface.c
@@ -725,7 +725,6 @@ int batadv_hardif_enable_interface(struct batadv_hard_iface *hard_iface,
 
 	kref_get(&hard_iface->refcount);
 
-	dev_hold(mesh_iface);
 	netdev_hold(mesh_iface, &hard_iface->meshif_dev_tracker, GFP_ATOMIC);
 	hard_iface->mesh_iface = mesh_iface;
 	bat_priv = netdev_priv(hard_iface->mesh_iface);

Re: [syzbot] [mm?] WARNING in move_to_new_folio

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com
Tested-by: syzbot+8bb6fd945af4e0ad9299@syzkaller.appspotmail.com

Tested on:

commit:         01c6df60 Add linux-next specific files for 20250411
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=166f7c04580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db03cefa26ecf825
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10d6c470580000

Note: testing is done by a robot and is best-effort only.