ext4: Make sure BH_New bit is cleared in ->write_end handler

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: 3910b51 ("ext4: persist the new uptodate buffers in ext4_journalled_zero_new_buffers")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250709084831.23876-2-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: jankara

fs/ext4/inline.c

@@ -612,6 +612,7 @@ 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,
@@ -891,6 +892,7 @@ 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);

fs/ext4/inode.c

@@ -1189,7 +1189,7 @@ 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);
@@ -1417,6 +1417,7 @@ 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;
 }