[PATCH v4 0/4] jbd2/ext4/ocfs2: lockless jinode dirty range

[Li Chen <me@linux.beauty>]

This series makes the jbd2_inode dirty range tracking safe for lockless
reads in jbd2 and filesystem callbacks used by ext4 and ocfs2.

Some paths access jinode fields without holding journal->j_list_lock
(e.g. fast commit helpers and ordered truncate helpers). v1 used READ_ONCE()
on i_dirty_start/end, but Matthew pointed out that loff_t can be torn on
32-bit platforms, and Jan suggested storing the dirty range in PAGE_SIZE
units as pgoff_t.

With this series, jbd2 stores the dirty range as page indexes and uses
READ_ONCE()/WRITE_ONCE() for lockless access. ext4 and ocfs2 use the new
jbd2_jinode_get_dirty_range() accessor which converts the page-based range
back to byte offsets for writeback.

This is based on Jan's suggestion in the review of the ext4 jinode
publication race fix. [1]

Changes since v3:
- Store i_dirty_end_page as an exclusive end page and drop the sentinel.
- Publish end_page before start_page and treat start_page >= end_page as
  empty.

Changes since v2:
- Add jbd2_jinode_get_dirty_range() accessor and convert ext4/ocfs2 to use it
  before switching the underlying representation (per Andreas).
- Rename the dirty range fields to i_dirty_start_page/end_page to make the
  PAGE_SIZE units explicit and avoid silent unit mismatches when bisecting.

Changes since v1:
- Store i_dirty_start/end in PAGE_SIZE units (pgoff_t) to avoid torn loads on
  32-bit (pointed out by Matthew, suggested by Jan).
- Use WRITE_ONCE() for i_dirty_* / i_flags updates in jbd2 (per Jan).
- Drop pointless READ_ONCE() on i_vfs_inode in jbd2_wait_inode_data (per Jan).
- Convert ext4/ocfs2 callbacks to translate page range to byte offsets.

[1]: https://lore.kernel.org/all/4jxwogttddiaoqbstlgou5ox6zs27ngjjz5ukrxafm2z5ijxod@so4eqnykiegj/

v3: https://lore.kernel.org/all/20260224092434.202122-1-me@linux.beauty/
v2: https://lore.kernel.org/all/20260219114645.778338-1-me@linux.beauty/
v1: https://lore.kernel.org/all/20260130031232.60780-1-me@linux.beauty/

Li Chen (4):
  jbd2: add jinode dirty range accessors
  ext4: use jbd2 jinode dirty range accessor
  ocfs2: use jbd2 jinode dirty range accessor
  jbd2: store jinode dirty range in PAGE_SIZE units

 fs/ext4/inode.c       | 10 ++++++--
 fs/ext4/super.c       | 16 +++++++++----
 fs/jbd2/commit.c      | 55 +++++++++++++++++++++++++++++++++----------
 fs/jbd2/journal.c     |  5 ++--
 fs/jbd2/transaction.c | 21 +++++++++++------
 fs/ocfs2/journal.c    |  9 +++++--
 include/linux/jbd2.h  | 38 ++++++++++++++++++++++++------
 7 files changed, 115 insertions(+), 39 deletions(-)

-- 
2.53.0