Re: [PATCH 03/17] xfs: don't lock the dquot before return in xqcheck_commit_dquot

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Oct 13, 2025 at 11:48:04AM +0900, Christoph Hellwig wrote:
> While xfs_qm_dqput requires the dquot to be locked, the callers can use
> the more common xfs_qm_dqrele helper that takes care of locking the dquot
> instead.

But the start of xqcheck_commit_dquot does:

	/* Unlock the dquot just long enough to allocate a transaction. */
	xfs_dqunlock(dq);
	error = xchk_trans_alloc(xqc->sc, 0);
>>	xfs_dqlock(dq);
	if (error)
		return error;

So that'll cause a livelock in xfs_qm_dqrele in the loop body below if
the transaction allocation fails.

--D

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/scrub/quotacheck_repair.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/xfs/scrub/quotacheck_repair.c b/fs/xfs/scrub/quotacheck_repair.c
> index 415314911499..67bdc872996a 100644
> --- a/fs/xfs/scrub/quotacheck_repair.c
> +++ b/fs/xfs/scrub/quotacheck_repair.c
> @@ -121,17 +121,12 @@ xqcheck_commit_dquot(
>  	 * the caller can put the reference (which apparently requires a locked
>  	 * dquot).
>  	 */
> -	error = xrep_trans_commit(xqc->sc);
> -	mutex_lock(&dq->q_qlock);
> -	return error;
> +	return xrep_trans_commit(xqc->sc);
>  
>  out_unlock:
>  	mutex_unlock(&xqc->lock);
>  out_cancel:
>  	xchk_trans_cancel(xqc->sc);
> -
> -	/* Re-lock the dquot so the caller can put the reference. */
> -	mutex_lock(&dq->q_qlock);
>  	return error;
>  }
>  
> @@ -156,7 +151,7 @@ xqcheck_commit_dqtype(
>  	xchk_dqiter_init(&cursor, sc, dqtype);
>  	while ((error = xchk_dquot_iter(&cursor, &dq)) == 1) {
>  		error = xqcheck_commit_dquot(xqc, dqtype, dq);
> -		xfs_qm_dqput(dq);
> +		xfs_qm_dqrele(dq);
>  		if (error)
>  			break;
>  	}
> @@ -187,7 +182,7 @@ xqcheck_commit_dqtype(
>  			return error;
>  
>  		error = xqcheck_commit_dquot(xqc, dqtype, dq);
> -		xfs_qm_dqput(dq);
> +		xfs_qm_dqrele(dq);
>  		if (error)
>  			return error;
>  
> -- 
> 2.47.3
> 
>