xfs: shutdown after buf release in iflush cluster abort path

If xfs_iflush_cluster() fails due to corruption, the error path
issues a shutdown and simulates an I/O completion to release the
buffer. This code has a couple small problems. First, the shutdown
sequence can issue a synchronous log force, which is unsafe to do
with buffer locks held. Second, the simulated I/O completion does not
guarantee the buffer is async and thus is unlocked and released.

For example, if the last operation on the buffer was a read off disk
prior to the corruption event, XBF_ASYNC is not set and the buffer
is left locked and held upon return. This results in a memory leak
as shown by the following message on module unload:

 BUG xfs_buf (...): Objects remaining in xfs_buf on __kmem_cache_shutdown()

Fix both of these problems by setting XBF_ASYNC on the buffer prior
to the simulated I/O error and performing the shutdown immediately
after ioend processing when the buffer has been released.
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_inode.c

@@ -3614,7 +3614,6 @@ xfs_iflush_cluster(
 	 * inode buffer and shut down the filesystem.
 	 */
 	rcu_read_unlock();
-	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
 
 	/*
 	 * We'll always have an inode attached to the buffer for completion
@@ -3624,11 +3623,14 @@ xfs_iflush_cluster(
 	 * xfs_buf_submit().
 	 */
 	ASSERT(bp->b_iodone);
+	bp->b_flags |= XBF_ASYNC;
 	bp->b_flags &= ~XBF_DONE;
 	xfs_buf_stale(bp);
 	xfs_buf_ioerror(bp, -EIO);
 	xfs_buf_ioend(bp);
 
+	xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
+
 	/* abort the corrupt inode, as it was not attached to the buffer */
 	xfs_iflush_abort(cip, false);
 	kmem_free(cilist);