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Message-ID: <20250430100150.279751-1-shivankg@amd.com>
Date: Wed, 30 Apr 2025 10:01:49 +0000
From: Shivank Garg <shivankg@....com>
To: <shaggy@...nel.org>, <akpm@...ux-foundation.org>
CC: <willy@...radead.org>, <shivankg@....com>, <david@...hat.com>,
<wangkefeng.wang@...wei.com>, <jane.chu@...cle.com>, <ziy@...dia.com>,
<donettom@...ux.ibm.com>, <apopple@...dia.com>,
<jfs-discussion@...ts.sourceforge.net>, <linux-kernel@...r.kernel.org>,
<linux-mm@...ck.org>, <syzbot+8bb6fd945af4e0ad9299@...kaller.appspotmail.com>
Subject: [PATCH V5 0/2] JFS: Implement migrate_folio for jfs_metapage_aops
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
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