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

Baolin Liu
2024-10-10T02:59:09Z

From: Baolin Liu <liubaolin@kylinos.cn>

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@sangfor.com.cn>
Suggested-by: Shida Zhang <zhangshida@kylinos.cn>
Signed-off-by: Baolin Liu <liubaolin@kylinos.cn>
---
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