[PATCH v4 RESEND] ext4: Make sure BH_New bit is cleared in ->write_end handler

[PATCH v4 RESEND] ext4: Make sure BH_New bit is cleared in ->write_end handler

[Jan Kara]

Currently we clear BH_New bit in case of error and also in the standard
ext4_write_end() handler (in block_commit_write()). However
ext4_journalled_write_end() misses this clearing and thus we are leaving
stale BH_New bits behind. Generally ext4_block_write_begin() clears
these bits before any harm can be done but in case blocksize < pagesize
and we hit some error when processing a page with these stale bits,
we'll try to zero buffers with these stale BH_New bits and jbd2 will
complain (as buffers were not prepared for writing in this transaction).
Fix the problem by clearing BH_New bits in ext4_journalled_write_end()
and WARN if ext4_block_write_begin() sees stale BH_New bits.

Reported-by: Baolin Liu <liubaolin12138@163.com>
Reported-by: Zhi Long <longzhi@sangfor.com.cn>
Fixes: 3910b513fcdf ("ext4: persist the new uptodate buffers in ext4_journalled_zero_new_buffers")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/inline.c | 2 ++
 fs/ext4/inode.c  | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

Hello Ted,

when clearing branches in my devel tree I've found this fix which I think
has fallen through the cracks so I'm resending it.

Changes since v3 (https://lore.kernel.org/all/20241113175550.GA462442@mit.edu):
  * Clear stale BH_New flags resulting from inline->extent data conversion

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 3536ca7e4fcc..0d3cf0ca5c2a 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -606,6 +606,7 @@ static int ext4_convert_inline_data_to_extent(struct address_space *mapping,
 	} else
 		ret = ext4_block_write_begin(handle, folio, from, to,
 					     ext4_get_block);
+	clear_buffer_new(folio_buffers(folio));
 
 	if (!ret && ext4_should_journal_data(inode)) {
 		ret = ext4_walk_page_buffers(handle, inode,
@@ -867,6 +868,7 @@ static int ext4_da_convert_inline_data_to_extent(struct address_space *mapping,
 		return ret;
 	}
 
+	clear_buffer_new(folio_buffers(folio));
 	folio_mark_dirty(folio);
 	folio_mark_uptodate(folio);
 	ext4_clear_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 54bdd4884fe6..aa56af4a92ad 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1049,7 +1049,7 @@ int ext4_block_write_begin(handle_t *handle, struct folio *folio,
 			}
 			continue;
 		}
-		if (buffer_new(bh))
+		if (WARN_ON_ONCE(buffer_new(bh)))
 			clear_buffer_new(bh);
 		if (!buffer_mapped(bh)) {
 			WARN_ON(bh->b_size != blocksize);
@@ -1265,6 +1265,7 @@ static int write_end_fn(handle_t *handle, struct inode *inode,
 	ret = ext4_dirty_journalled_data(handle, bh);
 	clear_buffer_meta(bh);
 	clear_buffer_prio(bh);
+	clear_buffer_new(bh);
 	return ret;
 }
 
-- 
2.35.3

Re: [PATCH v4 RESEND] ext4: Make sure BH_New bit is cleared in ->write_end handler

[Theodore Ts'o]

On Wed, 09 Jul 2025 10:48:32 +0200, Jan Kara wrote:
> Currently we clear BH_New bit in case of error and also in the standard
> ext4_write_end() handler (in block_commit_write()). However
> ext4_journalled_write_end() misses this clearing and thus we are leaving
> stale BH_New bits behind. Generally ext4_block_write_begin() clears
> these bits before any harm can be done but in case blocksize < pagesize
> and we hit some error when processing a page with these stale bits,
> we'll try to zero buffers with these stale BH_New bits and jbd2 will
> complain (as buffers were not prepared for writing in this transaction).
> Fix the problem by clearing BH_New bits in ext4_journalled_write_end()
> and WARN if ext4_block_write_begin() sees stale BH_New bits.
> 
> [...]

Applied, thanks!

[1/1] ext4: Make sure BH_New bit is cleared in ->write_end handler
      commit: 91b8ca8b26729b729dda8a4eddb9aceaea706f37

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>