Re: [PATCH 2/3] xfs: don't assert fail on perag references on teardown

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

On Tue, May 24, 2022 at 02:00:15PM +1000, Dave Chinner wrote:
> On Mon, May 23, 2022 at 08:48:06PM -0700, Darrick J. Wong wrote:
> > On Tue, May 24, 2022 at 12:21:57PM +1000, Dave Chinner wrote:
> > > From: Dave Chinner <dchinner@redhat.com>
> > > 
> > > Not fatal, the assert is there to catch developer attention. I'm
> > > seeing this occasionally during recoveryloop testing after a
> > > shutdown, and I don't want this to stop an overnight recoveryloop
> > > run as it is currently doing.
> > > 
> > > Convert the ASSERT to a XFS_IS_CORRUPT() check so it will dump a
> > > corruption report into the log and cause a test failure that way,
> > > but it won't stop the machine dead.
> > > 
> > > Signed-off-by: Dave Chinner <dchinner@redhat.com>
> > > ---
> > >  fs/xfs/libxfs/xfs_ag.c | 3 +--
> > >  1 file changed, 1 insertion(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c
> > > index 1e4ee042d52f..3e920cf1b454 100644
> > > --- a/fs/xfs/libxfs/xfs_ag.c
> > > +++ b/fs/xfs/libxfs/xfs_ag.c
> > > @@ -173,7 +173,6 @@ __xfs_free_perag(
> > >  	struct xfs_perag *pag = container_of(head, struct xfs_perag, rcu_head);
> > >  
> > >  	ASSERT(!delayed_work_pending(&pag->pag_blockgc_work));
> > > -	ASSERT(atomic_read(&pag->pag_ref) == 0);
> > 
> > Er, shouldn't this also be converted to XFS_IS_CORRUPT?  That's what the
> > commit message said...
> 
> That's in the RCU callback context and we never get here when the
> ASSERT fires. i.e. the assert in xfs_free_perag fires before we
> queue the rcu callback to free this, so checking it here is kinda
> redundant.
> 
> i.e. it's not where this issue is being caught - it's
> being caught by the check below (in xfs_free_perag()) where the
> conversion to XFS_IS_CORRUPT is done....

Ah, right.  Ok then,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> Cheers,
> 
> Dave.
> 
> > >  	kmem_free(pag);
> > >  }
> > >  
> > > @@ -192,7 +191,7 @@ xfs_free_perag(
> > >  		pag = radix_tree_delete(&mp->m_perag_tree, agno);
> > >  		spin_unlock(&mp->m_perag_lock);
> > >  		ASSERT(pag);
> > > -		ASSERT(atomic_read(&pag->pag_ref) == 0);
> > > +		XFS_IS_CORRUPT(pag->pag_mount, atomic_read(&pag->pag_ref) != 0);
> > >  
> > >  		cancel_delayed_work_sync(&pag->pag_blockgc_work);
> > >  		xfs_iunlink_destroy(pag);
> > > -- 
> > > 2.35.1
> > > 
> > 
> 
> -- 
> Dave Chinner
> david@fromorbit.com