Re: [PATCH] jbd2: fix off-by-one while erasing journal

[Baokun Li <libaokun1@huawei.com>]

On 2025/2/17 14:59, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@huawei.com>
>
> In __jbd2_journal_erase(), the block_stop parameter includes the last
> block of a contiguous region; however, the calculation of byte_stop is
> incorrect, as it does not account for the bytes in that last block.
> Consequently, the page cache is not cleared properly, which occasionally
> causes the ext4/050 test to fail.
>
> Since block_stop operates on inclusion semantics, it involves repeated
> increments and decrements by 1, significantly increasing the complexity
> of the calculations. Optimize the calculation and fix the incorrect
> byte_stop by make both block_stop and byte_stop to use exclusion
> semantics.
>
> This fixes a failure in fstests ext4/050.
>
> Fixes: 01d5d96542fd ("ext4: add discard/zeroout flags to journal flush")
> Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Looks good, thanks for the patch!

Reviewed-by: Baokun Li <libaokun1@huawei.com>
> ---
>   fs/jbd2/journal.c | 15 ++++++---------
>   1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index d8084b31b361..49a9e99cbc03 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1965,17 +1965,15 @@ static int __jbd2_journal_erase(journal_t *journal, unsigned int flags)
>   			return err;
>   		}
>   
> -		if (block_start == ~0ULL) {
> -			block_start = phys_block;
> -			block_stop = block_start - 1;
> -		}
> +		if (block_start == ~0ULL)
> +			block_stop = block_start = phys_block;
>   
>   		/*
>   		 * last block not contiguous with current block,
>   		 * process last contiguous region and return to this block on
>   		 * next loop
>   		 */
> -		if (phys_block != block_stop + 1) {
> +		if (phys_block != block_stop) {
>   			block--;
>   		} else {
>   			block_stop++;
> @@ -1994,11 +1992,10 @@ static int __jbd2_journal_erase(journal_t *journal, unsigned int flags)
>   		 */
>   		byte_start = block_start * journal->j_blocksize;
>   		byte_stop = block_stop * journal->j_blocksize;
> -		byte_count = (block_stop - block_start + 1) *
> -				journal->j_blocksize;
> +		byte_count = (block_stop - block_start) * journal->j_blocksize;
>   
>   		truncate_inode_pages_range(journal->j_dev->bd_mapping,
> -				byte_start, byte_stop);
> +				byte_start, byte_stop - 1);
>   
>   		if (flags & JBD2_JOURNAL_FLUSH_DISCARD) {
>   			err = blkdev_issue_discard(journal->j_dev,
> @@ -2013,7 +2010,7 @@ static int __jbd2_journal_erase(journal_t *journal, unsigned int flags)
>   		}
>   
>   		if (unlikely(err != 0)) {
> -			pr_err("JBD2: (error %d) unable to wipe journal at physical blocks %llu - %llu",
> +			pr_err("JBD2: (error %d) unable to wipe journal at physical blocks [%llu, %llu)",
>   					err, block_start, block_stop);
>   			return err;
>   		}