xfs: fix inode validity check in xfs_iflush_cluster

xfs: fix inode validity check in xfs_iflush_cluster

Orabug: 25256935

[ Upstream commit 51b07f30a71c27405259a0248206ed4e22adbee2 ]

Some careless idiot(*) wrote crap code in commit 1a3e8f3 ("xfs:
convert inode cache lookups to use RCU locking") back in late 2010,
and so xfs_iflush_cluster checks the wrong inode for whether it is
still valid under RCU protection. Fix it to lock and check the
correct inode.

(*) Careless-idiot: Dave Chinner <dchinner@redhat.com>

cc: <stable@vger.kernel.org> # 3.10.x-
Discovered-by: Brain Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
(cherry picked from commit 3eeb7e764de82bba421e04154bb62b8dc518c3a1)
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>