Re: [PATCH 2/3] ext4: check return value of blkdev_issue_flush() when starting a fast commit

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] ext4: missing JBD2_BARRIER check for fast commit device flush
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commit a1cae98067fdb2cd8eec738283b6d33c84b7ca8d
Author: guolingxing <guolingxing@tju.edu.cn>

ext4: check return value of blkdev_issue_flush() when starting a fast commit

When the file system device differs from the journal device, a cache flush
is issued before fast commit blocks are written. The return value of
blkdev_issue_flush() was previously ignored. This patch checks the return
value and aborts the fast commit if the flush fails, falling back to a full
journal commit.

> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> index 0cac890cf3702..ead8b16f9be07 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> @@ -1425,8 +1425,11 @@ static int ext4_fc_perform_commit(journal_t *journal, tid_t commit_tid)
>  	 * Step 5: If file system device is different from journal device,
>  	 * issue a cache flush before we start writing fast commit blocks.
>  	 */
> -	if (journal->j_fs_dev != journal->j_dev)
> -		blkdev_issue_flush(journal->j_fs_dev);
> +	if (journal->j_fs_dev != journal->j_dev) {
> +		ret = blkdev_issue_flush(journal->j_fs_dev);
> +		if (ret)
> +			return ret;
> +	}

[Severity: Medium]
This problem wasn't introduced by this patch, but does this flush need to
validate journal->j_flags & JBD2_BARRIER before proceeding?

In ext4_fc_perform_commit(), blkdev_issue_flush() is called unconditionally
when the filesystem device differs from the journal device. If the filesystem
is mounted with the "nobarrier" option, this appears to ignore the mount
option and issue the cache flush anyway, unlike the JBD2 full commit path and
fast commit tail block writers.

Could this bypass the user's mount options and cause unnecessary I/O
overhead during fast commits?

>  
>  	blk_start_plug(&plug);
>  	alloc_ctx = ext4_fc_lock(sb);

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Sashiko AI review · https://sashiko.dev/#/patchset/20261013062618.1741670-1-guolingxing@tju.edu.cn?part=2