pNFS: Fix race in pnfs_wait_on_layoutreturn

commit ee284e35d8 upstream.

We must put the task to sleep while holding the inode->i_lock in order
to ensure atomicity with the test for NFS_LAYOUT_RETURN.

Fixes: 500d701f33 ("NFS41: make close wait for layoutreturn")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/nfs/pnfs.c

@@ -1185,13 +1185,11 @@ bool pnfs_wait_on_layoutreturn(struct inode *ino, struct rpc_task *task)
 	 * i_lock */
         spin_lock(&ino->i_lock);
         lo = nfsi->layout;
-        if (lo && test_bit(NFS_LAYOUT_RETURN, &lo->plh_flags))
-                sleep = true;
-        spin_unlock(&ino->i_lock);
-
-        if (sleep)
+        if (lo && test_bit(NFS_LAYOUT_RETURN, &lo->plh_flags)) {
                 rpc_sleep_on(&NFS_SERVER(ino)->roc_rpcwaitq, task, NULL);
-
+                sleep = true;
+	}
+        spin_unlock(&ino->i_lock);
         return sleep;
 }