[PATCH v1] ext4: fix a assertion failure due to ungranted bh dirting

[Baolin Liu]

From: Baolin Liu <liubaolin@xxxxxxxxxx>

Since the merge of commit 3910b513fcdf ("ext4: persist the new uptodate
buffers in ext4_journalled_zero_new_buffers"), a new assertion failure
occurred under a old kernel(ext3, data=journal, pagesize=64k) with
corresponding ported patches:
================================================================
Call trace:
  __ext4_handle_dirty_metadata+0x320/0x7e8
  write_end_fn+0x78/0x178
  ext4_journalled_zero_new_buffers+0xd0/0x2c8
  ext4_block_write_begin+0x850/0xc00
  ext4_write_begin+0x334/0xc68
  generic_perform_write+0x1a4/0x380
  ext4_buffered_write_iter+0x180/0x370
  ext4_file_write_iter+0x194/0xfc0
  new_sync_write+0x338/0x4b8
  __vfs_write+0xc4/0xe8
  vfs_write+0x12c/0x3d0
  ksys_write+0xf4/0x230
  sys_write+0x34/0x48
  el0_svc_naked+0x44/0x48
================================================================

which was caused by bh dirting without calling
do_journal_get_write_access().

In the loop for all bhs of a page in ext4_block_write_begin(),
when a err occurred, it will jump out of loop.
But that will leaves some bhs being processed and some not,
which will lead to the asserion failure in calling write_end_fn().

To fixed that, get write access for the rest unprocessed bhs, just
as what write_end_fn do.

Fixes: 3910b513fcdf ("ext4: persist the new uptodate buffers in ext4_journalled_zero_new_buffers")
Reported-and-tested-by: Zhi Long <longzhi@xxxxxxxxxxxxxx>
Suggested-by: Shida Zhang <zhangshida@xxxxxxxxxx>
Signed-off-by: Baolin Liu <liubaolin@xxxxxxxxxx>
---
 fs/ext4/inode.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 54bdd4884fe6..a72f951288e4 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1102,9 +1102,24 @@ int ext4_block_write_begin(handle_t *handle, struct folio *folio,
 			err = -EIO;
 	}
 	if (unlikely(err)) {
-		if (should_journal_data)
+		if (should_journal_data) {
+			if (bh != head || !block_start) {
+				do {
+					block_end = block_start + bh->b_size;
+
+					if (buffer_new(bh))
+						if (block_end > from && block_start < to)
+							do_journal_get_write_access(handle,
+										    inode, bh);
+
+					block_start = block_end;
+					bh = bh->b_this_page;
+				} while (bh != head);
+			}
+
 			ext4_journalled_zero_new_buffers(handle, inode, folio,
 							 from, to);
+		}
 		else
 			folio_zero_new_buffers(folio, from, to);
 	} else if (fscrypt_inode_uses_fs_layer_crypto(inode)) {
-- 
2.39.2