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* [syzbot] [mm?] WARNING in move_to_new_folio
@ 2025-04-13  0:03 syzbot
  2025-04-13  6:24 ` syzbot
                   ` (2 more replies)
  0 siblings, 3 replies; 20+ messages in thread
From: syzbot @ 2025-04-13  0:03 UTC (permalink / raw)
  To: akpm, linux-kernel, linux-mm, syzkaller-bugs

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>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

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

^ permalink raw reply	[flat|nested] 20+ messages in thread
[parent not found: <60d9e567-cc9a-43fb-a47e-e8aba30cc98e@amd.com>]
* [PATCH V3 0/2] JFS: Implement migrate_folio for jfs_metapage_aops
@ 2025-04-17  6:06 Shivank Garg
  2025-04-17  8:47 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot
  0 siblings, 1 reply; 20+ messages in thread
From: Shivank Garg @ 2025-04-17  6:06 UTC (permalink / raw)
  To: shaggy, akpm
  Cc: willy, shivankg, david, wangkefeng.wang, jane.chu, ziy, donettom,
	apopple, jfs-discussion, linux-kernel, linux-mm,
	syzbot+8bb6fd945af4e0ad9299

This patch addresses a warning that occurs during memory compaction due
to JFS's missing migrate_folio operation. The warning was introduced by
commit 7ee3647 ("migrate: Remove call to ->writepage") which added
explicit warnings when filesystem don't implement migrate_folio.

The syzbot reported following [1]:
  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

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

[1]: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299

V1/V2:
https://lore.kernel.org/all/20250413172356.561544-1-shivankg@amd.com

#syz test: https://github.com/AMDESE/linux-mm.git 07246f14ea

Best Regards,
Shivank

Shivank Garg (2):
  mm: export folio_expected_refs for JFS migration handler
  jfs: implement migrate_folio for jfs_metapage_aops

 fs/jfs/jfs_metapage.c   | 94 +++++++++++++++++++++++++++++++++++++++++
 include/linux/migrate.h |  1 +
 mm/migrate.c            |  3 +-
 3 files changed, 97 insertions(+), 1 deletion(-)

-- 
2.34.1


^ permalink raw reply	[flat|nested] 20+ messages in thread
* [PATCH V4 0/2] JFS: Implement migrate_folio for jfs_metapage_aops
@ 2025-04-22 11:40 Shivank Garg
  2025-04-22 13:59 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot
  0 siblings, 1 reply; 20+ messages in thread
From: Shivank Garg @ 2025-04-22 11:40 UTC (permalink / raw)
  To: shaggy, akpm
  Cc: willy, shivankg, david, wangkefeng.wang, jane.chu, ziy, donettom,
	apopple, jfs-discussion, linux-kernel, linux-mm,
	syzbot+8bb6fd945af4e0ad9299

This patch addresses a warning that occurs during memory compaction due
to JFS's missing migrate_folio operation. The warning was introduced by
commit 7ee3647243e5 ("migrate: Remove call to ->writepage") which added
explicit warnings when filesystem don't implement migrate_folio.

The syzbot reported following [1]:
  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

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

[1]: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299

Previous Versions:
V1/V2:
https://lore.kernel.org/all/20250413172356.561544-1-shivankg@amd.com
V3:
https://lore.kernel.org/all/20250417060630.197278-1-shivankg@amd.com

#syz test: https://github.com/AMDESE/linux-mm.git f17a3b8bc


Shivank Garg (2):
  mm: export folio_expected_refs for JFS migration handler
  jfs: implement migrate_folio for jfs_metapage_aops

 fs/jfs/jfs_metapage.c   | 94 +++++++++++++++++++++++++++++++++++++++++
 include/linux/migrate.h |  1 +
 mm/migrate.c            |  3 +-
 3 files changed, 97 insertions(+), 1 deletion(-)

-- 
2.34.1


^ permalink raw reply	[flat|nested] 20+ messages in thread
* Syz Test if issue still reproduce
@ 2025-04-30  5:12 Shivank Garg
  2025-04-30  7:30 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot
  0 siblings, 1 reply; 20+ messages in thread
From: Shivank Garg @ 2025-04-30  5:12 UTC (permalink / raw)
  To: linux-kernel, syzbot

Hi,

Testing if this issue https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299
still reproduces


#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git 33035b665

diff --git a/fs/jfs/jfs_metapage.c b/fs/jfs/jfs_metapage.c
index df575a873ec6..f863ba521533 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 (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_ref_count(src) + 1;
+	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/mm.h b/include/linux/mm.h
index 68d3dd14b323..1db540bb9381 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2115,6 +2115,61 @@ static inline bool folio_maybe_mapped_shared(struct folio *folio)
 	return folio_test_large_maybe_mapped_shared(folio);
 }
 
+/**
+ * folio_expected_ref_count - calculate the expected folio refcount
+ * @folio: the folio
+ *
+ * Calculate the expected folio refcount, taking references from the pagecache,
+ * swapcache, PG_private and page table mappings into account. Useful in
+ * combination with folio_ref_count() to detect unexpected references (e.g.,
+ * GUP or other temporary references).
+ *
+ * Does currently not consider references from the LRU cache. If the folio
+ * was isolated from the LRU (which is the case during migration or split),
+ * the LRU cache does not apply.
+ *
+ * Calling this function on an unmapped folio -- !folio_mapped() -- that is
+ * locked will return a stable result.
+ *
+ * Calling this function on a mapped folio will not result in a stable result,
+ * because nothing stops additional page table mappings from coming (e.g.,
+ * fork()) or going (e.g., munmap()).
+ *
+ * Calling this function without the folio lock will also not result in a
+ * stable result: for example, the folio might get dropped from the swapcache
+ * concurrently.
+ *
+ * However, even when called without the folio lock or on a mapped folio,
+ * this function can be used to detect unexpected references early (for example,
+ * if it makes sense to even lock the folio and unmap it).
+ *
+ * The caller must add any reference (e.g., from folio_try_get()) it might be
+ * holding itself to the result.
+ *
+ * Returns the expected folio refcount.
+ */
+static inline int folio_expected_ref_count(const struct folio *folio)
+{
+	const int order = folio_order(folio);
+	int ref_count = 0;
+
+	if (WARN_ON_ONCE(folio_test_slab(folio)))
+		return 0;
+
+	if (folio_test_anon(folio)) {
+		/* One reference per page from the swapcache. */
+		ref_count += folio_test_swapcache(folio) << order;
+	} else if (!((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS)) {
+		/* One reference per page from the pagecache. */
+		ref_count += !!folio->mapping << order;
+		/* One reference from PG_private. */
+		ref_count += folio_test_private(folio);
+	}
+
+	/* One reference per page table mapping. */
+	return ref_count + folio_mapcount(folio);
+}
+
 #ifndef HAVE_ARCH_MAKE_FOLIO_ACCESSIBLE
 static inline int arch_make_folio_accessible(struct folio *folio)
 {
diff --git a/mm/migrate.c b/mm/migrate.c
index c80591514e66..67f2bf1eb51e 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -445,20 +445,6 @@ void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 }
 #endif
 
-static int folio_expected_refs(struct address_space *mapping,
-		struct folio *folio)
-{
-	int refs = 1;
-	if (!mapping)
-		return refs;
-
-	refs += folio_nr_pages(folio);
-	if (folio_test_private(folio))
-		refs++;
-
-	return refs;
-}
-
 /*
  * Replace the folio in the mapping.
  *
@@ -601,7 +587,7 @@ static int __folio_migrate_mapping(struct address_space *mapping,
 int folio_migrate_mapping(struct address_space *mapping,
 		struct folio *newfolio, struct folio *folio, int extra_count)
 {
-	int expected_count = folio_expected_refs(mapping, folio) + extra_count;
+	int expected_count = folio_expected_ref_count(folio) + extra_count + 1;
 
 	if (folio_ref_count(folio) != expected_count)
 		return -EAGAIN;
@@ -618,7 +604,7 @@ int migrate_huge_page_move_mapping(struct address_space *mapping,
 				   struct folio *dst, struct folio *src)
 {
 	XA_STATE(xas, &mapping->i_pages, folio_index(src));
-	int rc, expected_count = folio_expected_refs(mapping, src);
+	int rc, expected_count = folio_expected_ref_count(src) + 1;
 
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
@@ -749,7 +735,7 @@ static int __migrate_folio(struct address_space *mapping, struct folio *dst,
 			   struct folio *src, void *src_private,
 			   enum migrate_mode mode)
 {
-	int rc, expected_count = folio_expected_refs(mapping, src);
+	int rc, expected_count = folio_expected_ref_count(src) + 1;
 
 	/* Check whether src does not have extra refs before we do more work */
 	if (folio_ref_count(src) != expected_count)
@@ -837,7 +823,7 @@ static int __buffer_migrate_folio(struct address_space *mapping,
 		return 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);
+	expected_count = folio_expected_ref_count(src) + 1;
 	if (folio_ref_count(src) != expected_count)
 		return -EAGAIN;
 


^ permalink raw reply related	[flat|nested] 20+ messages in thread
* [PATCH V5 0/2]  JFS: Implement migrate_folio for jfs_metapage_aops
@ 2025-04-30 10:01 Shivank Garg
  2025-04-30 10:38 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot
  0 siblings, 1 reply; 20+ messages in thread
From: Shivank Garg @ 2025-04-30 10:01 UTC (permalink / raw)
  To: shaggy, akpm
  Cc: willy, shivankg, david, wangkefeng.wang, jane.chu, ziy, donettom,
	apopple, jfs-discussion, linux-kernel, linux-mm,
	syzbot+8bb6fd945af4e0ad9299

This patch addresses a warning that occurs during memory compaction due
to JFS's missing migrate_folio operation. The warning was introduced by
commit 7ee3647243e5 ("migrate: Remove call to ->writepage") which added
explicit warnings when filesystem don't implement migrate_folio.

The syzbot reported following [1]:
  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

To fix this issue, this series implement metapage_migrate_folio() for JFS
which handles both single and multiple metapages per page configurations.

While most filesystems leverage existing migration implementations like
filemap_migrate_folio(), buffer_migrate_folio_norefs() or buffer_migrate_folio()
(which internally used folio_expected_refs()), JFS's metapage architecture
requires special handling of its private data during migration. To support this,
this series introduce the folio_expected_ref_count(), which calculates
external references to a folio from page/swap cache, private data, and page
table mappings.
This standardized implementation replaces the previous ad-hoc
folio_expected_refs() function and enables JFS to accurately determine whether
a folio has unexpected references before attempting migration.

[1]: https://syzkaller.appspot.com/bug?extid=8bb6fd945af4e0ad9299

Changelogs:
V5 (current):
- Add folio_expected_ref_count() for refcount calculation
- Add details about need of folio_expected_ref_count() for JFS

V4:
- https://lore.kernel.org/all/20250422114000.15003-1-shivankg@amd.com
- Make folio_expected_refs() inline and rename to folio_migration_expected_refs()

V3:
- https://lore.kernel.org/all/20250417060630.197278-1-shivankg@amd.com
- Fix typos

V1/V2:
- https://lore.kernel.org/all/20250413172356.561544-1-shivankg@amd.com
- Implement metapage_migrate_folio() similar to buffer_migrate_folio() but
  specialized to move JFS metapage data

#syz test: https://github.com/shivankgarg98/linux.git 69a58d5260

Shivank Garg (2):
  mm: Add folio_expected_ref_count() for reference count calculation
  jfs: implement migrate_folio for jfs_metapage_aops

 fs/jfs/jfs_metapage.c | 94 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h    | 55 +++++++++++++++++++++++++
 mm/migrate.c          | 22 ++--------
 3 files changed, 153 insertions(+), 18 deletions(-)

-- 
2.34.1


^ permalink raw reply	[flat|nested] 20+ messages in thread
end of thread, other threads:[~2025-04-30 10:38 UTC | newest]

Thread overview: 20+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-04-13  0:03 [syzbot] [mm?] WARNING in move_to_new_folio syzbot
2025-04-13  6:24 ` syzbot
2025-04-13 21:44 ` syzbot
2025-04-15  4:57   ` Shivank Garg
2025-04-15  5:24     ` syzbot
2025-04-15  5:40       ` Shivank Garg
2025-04-15  6:00         ` syzbot
2025-04-15  6:18         ` Shivank Garg
2025-04-15  7:00           ` syzbot
2025-04-15  4:33 ` [syzbot] " syzbot
     [not found] <60d9e567-cc9a-43fb-a47e-e8aba30cc98e@amd.com>
2025-04-15  4:58 ` syzbot
  -- strict thread matches above, loose matches on Subject: below --
2025-04-17  6:06 [PATCH V3 0/2] JFS: Implement migrate_folio for jfs_metapage_aops Shivank Garg
2025-04-17  8:47 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot
2025-04-17  9:06   ` Shivank Garg
2025-04-22 11:40 [PATCH V4 0/2] JFS: Implement migrate_folio for jfs_metapage_aops Shivank Garg
2025-04-22 13:59 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot
2025-04-30  5:12 Syz Test if issue still reproduce Shivank Garg
2025-04-30  7:30 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot
2025-04-30  7:58   ` Shivank Garg
2025-04-30  8:23     ` syzbot
2025-04-30  9:06       ` Shivank Garg
2025-04-30  9:43         ` syzbot
2025-04-30 10:01 [PATCH V5 0/2] JFS: Implement migrate_folio for jfs_metapage_aops Shivank Garg
2025-04-30 10:38 ` [syzbot] [mm?] WARNING in move_to_new_folio syzbot

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