On Fri 23-08-24 09:33:29, zhangshida wrote:
> From: Shida Zhang <zhangshida@xxxxxxxxxx>
>
> On an old kernel version(4.19, ext3, data=journal, pagesize=64k),
> an assertion failure will occasionally be triggered by the line below:
> -----------
> jbd2_journal_commit_transaction
> {
> ...
> J_ASSERT_BH(bh, !buffer_dirty(bh));
> /*
> * The buffer on BJ_Forget list and not jbddirty means
> ...
> }
> -----------
>
> The same condition may also be applied to the lattest kernel version.
>
> When blocksize < pagesize and we truncate a file, there can be buffers in
> the mapping tail page beyond i_size. These buffers will be filed to
> transaction's BJ_Forget list by ext4_journalled_invalidatepage() during
> truncation. When the transaction doing truncate starts committing, we can
> grow the file again. This calls __block_write_begin() which allocates new
> blocks under these buffers in the tail page we go through the branch:
^^ and we...
> if (buffer_new(bh)) {
> clean_bdev_bh_alias(bh);
> if (folio_test_uptodate(folio)) {
> clear_buffer_new(bh);
> set_buffer_uptodate(bh);
> mark_buffer_dirty(bh);
> continue;
> }
> ...
> }
>
> Hence buffers on BJ_Forget list of the committing transaction get marked
> dirty and this triggers the jbd2 assertion.
>
> Teach ext4_block_write_begin() to properly handle files with data
> journalling by avoiding dirtying them directly. Instead of
> folio_zero_new_buffers() we use ext4_journalled_zero_new_buffers() which
> takes care of handling journalling. We also don't need to mark new uptodate
> buffers as dirty in ext4_block_write_begin(). That will be either done
> either by block_commit_write() in case of success or by
> folio_zero_new_buffers() in case of failure.
>
> Reported-by: Baolin Liu <liubaolin@xxxxxxxxxx>
> Suggested-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Shida Zhang <zhangshida@xxxxxxxxxx>
Looks mostly good. Just three small comments:
> @@ -1083,11 +1090,11 @@ int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
> err = get_block(inode, block, bh, 1);
> if (err)
> break;
> + if (should_journal_data)
> + do_journal_get_write_access(handle, inode, bh);
I'd move this inside the buffer_new() branch and add before it a comment:
/*
* We may be zeroing partial buffers or all new
* buffers in case of failure. Prepare JBD2 for
* that.
*/
> if (buffer_new(bh)) {
> if (folio_test_uptodate(folio)) {
> - clear_buffer_new(bh);
> set_buffer_uptodate(bh);
> - mark_buffer_dirty(bh);
Here I'd add comment:
/*
* Unlike __block_write_begin() we leave
* dirtying of new uptodate buffers to
* ->write_end() time or
* folio_zero_new_buffers().
*/
> @@ -1117,7 +1124,11 @@ int ext4_block_write_begin(struct folio *folio, loff_t pos, unsigned len,
> err = -EIO;
> }
> if (unlikely(err)) {
> - folio_zero_new_buffers(folio, from, to);
> + if (should_journal_data)
> + ext4_journalled_zero_new_buffers(handle, inode, folio,
> + from, to);
I've realized there's a small bug in ext4_journalled_zero_new_buffers()
that it calls write_end_fn() only if it zeroed a buffer. But for new
uptodate buffers we also need to call write_end_fn() to persist the
uptodate content (similarly as folio_zero_new_buffers() does it). So we
need another preparatory patch moving write_end_fn() in
ext4_journalled_zero_new_buffers() to be called also for uptodate pages.
> + else
> + folio_zero_new_buffers(folio, from, to);
> }
> #ifdef CONFIG_FS_ENCRYPTION
> else if (fscrypt_inode_uses_fs_layer_crypto(inode)) {
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
