nilfs2: force clear dirty state when restoring from the shadow map

When garbage collection fails, nilfs2 rolls the DAT metadata file's page
cache back to a shadow copy taken before GC started.
nilfs_clear_dirty_pages() drops the dirty state of the folios in the DAT
cache, then nilfs_copy_back_pages() overwrites them with the saved
contents and warns if one is still dirty:

	/* overwrite existing folio in the destination cache */
	WARN_ON(folio_test_dirty(dfolio));

nilfs_clear_dirty_pages() used to clear the dirty state unconditionally,
which is safe here because the rollback runs with the log writer
stopped, so nothing else can dirty the cache while it runs.  The same
helper is also used when writeback finds dirty folios after the
filesystem has degraded to read-only, where it does run concurrently
with the log writer, so commit ca76bb226bf4 ("nilfs2: do not force clear
folio if buffer is referenced") made nilfs_clear_folio_dirty() skip a
folio if any of its buffer heads is busy.  The rollback caller shares
that helper, so its clearing step can now return with a folio still
dirty.

A DAT folio can hold a busy buffer head without anyone modifying the
folio: nilfs_mdt_read_block() submits read-ahead for the blocks
following the one it was asked for and waits only for the first, so the
read-ahead buffers are still locked when it returns.  With a block size
smaller than the page size, a locked read-ahead buffer can share a folio
with a block that GC dirtied and keep the whole folio dirty past the
clearing step.

Add a force flag to nilfs_clear_dirty_pages() and
nilfs_clear_folio_dirty() that skips the busy buffer check, and set it
in the two calls from nilfs_mdt_restore_from_shadow_map().  The
read-only fallback callers keep passing false, so that commit still
protects them and the WARN_ON() is left alone.

Fixes: ca76bb226bf4 ("nilfs2: do not force clear folio if buffer is referenced")
Closes: https://lore.kernel.org/lkml/CANypQFZSYrtcshnUzOPiqatyLd-M8_OReOewQoAi_V5yY0dTtg@mail.gmail.com/
Cc: stable@vger.kernel.org
Suggested-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Assisted-by: Claude Code:claude-opus-5
Signed-off-by: Jiaming Zhang <r772577952@gmail.com>
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

0 files changed, 0 insertions, 0 deletions