xfs: don't assert fail on perag references on teardown

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>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

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);
 	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);