Re: [PATCH] xfs: retry dqpurge when dquot buffer is busy

[Darrick J. Wong]

On Fri, Jun 26, 2026 at 05:52:53PM +0800, Yingjie Gao wrote:
> xfs_qm_dqpurge() marks a zero-reference dquot dead before trying to flush
> a dirty dquot. If the attached buffer is busy, xfs_dquot_use_attached_buf()
> returns -EAGAIN.
> 
> The error path restores q_lockref.count but then jumps to out_funlock,
> which continues into the successful purge tail and destroys the dquot.  At
> that point the attached buffer has not been detached and the dquot log item
> may still be in the AIL.
> 
> Restore the retry behavior by dropping the locks and returning -EAGAIN
> after resurrecting the lockref.
> 
> Link: https://lore.kernel.org/linux-xfs/20260625175519.GF6078@frogsfrogsfrogs/
> Fixes: 0c5e80bd579f ("xfs: use a lockref for the xfs_dquot reference count")
> Cc: stable@xxxxxxxxxxxxxxx # v6.19+
> Signed-off-by: Yingjie Gao <gaoyingjie@xxxxxxxxxxxxx>

Yeah, that's more like what we did before 0c5e80bd579f.  I think the
lockref resurrection part still looks ok, but maybe hch has an opinion?

Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>

--D

> ---
>  fs/xfs/xfs_qm.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
> index aa0d2976f1c3..0622c72292d8 100644
> --- a/fs/xfs/xfs_qm.c
> +++ b/fs/xfs/xfs_qm.c
> @@ -155,8 +155,12 @@ xfs_qm_dqpurge(
>  		error = xfs_dquot_use_attached_buf(dqp, &bp);
>  		if (error == -EAGAIN) {
>  			/* resurrect the refcount from the dead. */
> +			xfs_dqfunlock(dqp);
> +			mutex_unlock(&dqp->q_qlock);
> +			spin_lock(&dqp->q_lockref.lock);
>  			dqp->q_lockref.count = 0;
> -			goto out_funlock;
> +			spin_unlock(&dqp->q_lockref.lock);
> +			return -EAGAIN;
>  		}
>  		if (!bp)
>  			goto out_funlock;
> -- 
> 2.20.1
> 
>