Re: [PATCH] xfs: fix unreachable BIGTIME check in dquot flush validation

[Allison Henderson <achender@kernel.org>]

On Wed, 2026-06-03 at 14:08 -0700, Darrick J. Wong wrote:
> [fix some addresses]
> 
> On Wed, Jun 03, 2026 at 08:41:47PM +0000, Alexey Nepomnyashih wrote:
> > The dqp->q_id == 0 check inside the XFS_DQTYPE_BIGTIME block is
> > unreachable because root dquots return successfully earlier. Reject root
> > dquots with XFS_DQTYPE_BIGTIME before that early return, preserving the
> > intended validation and removing the unreachable condition.
> > 
> > Found by Linux Verification Center (linuxtesting.org) with SVACE.
> > 
> > Fixes: 4ea1ff3b4968 ("xfs: widen ondisk quota expiration timestamps to handle y2038+")
> > Cc: stable@vger.kernel.org # v5.10+
> > Signed-off-by: Alexey Nepomnyashih <sdl@nppct.ru>
Hi Alexey,

Looks good, thanks for catching this!
Reviewed-by: Allison Henderson <achender@kernel.org>

> 
> Yeah, that looks like a screwup...
> Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
> 
> --D
> 
> > ---
> >  fs/xfs/xfs_dquot.c | 16 ++++++++--------
> >  1 file changed, 8 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c
> > index 69e9bc588c8b..c311f61d9554 100644
> > --- a/fs/xfs/xfs_dquot.c
> > +++ b/fs/xfs/xfs_dquot.c
> > @@ -1216,6 +1216,14 @@ xfs_qm_dqflush_check(
> >  	    type != XFS_DQTYPE_PROJ)
> >  		return __this_address;
> >  
> > +	/* bigtime flag should never be set on root dquots */
> > +	if (dqp->q_type & XFS_DQTYPE_BIGTIME) {
> > +		if (!xfs_has_bigtime(dqp->q_mount))
> > +			return __this_address;
> > +		if (dqp->q_id == 0)
> > +			return __this_address;
> > +	}
> > +
> >  	if (dqp->q_id == 0)
> >  		return NULL;
> >  
> > @@ -1231,14 +1239,6 @@ xfs_qm_dqflush_check(
> >  	    !dqp->q_rtb.timer)
> >  		return __this_address;
> >  
> > -	/* bigtime flag should never be set on root dquots */
> > -	if (dqp->q_type & XFS_DQTYPE_BIGTIME) {
> > -		if (!xfs_has_bigtime(dqp->q_mount))
> > -			return __this_address;
> > -		if (dqp->q_id == 0)
> > -			return __this_address;
> > -	}
> > -
> >  	return NULL;
> >  }
> >  
> > -- 
> > 2.43.0
> > 
> >