ceph: don't set req->r_locked_dir in ceph_d_revalidate

This function sets req->r_locked_dir which is supposed to indicate to
ceph_fill_trace that the parent's i_rwsem is locked for write.
Unfortunately, there is no guarantee that the dir will be locked when
d_revalidate is called, so we really don't want ceph_fill_trace to do
any dcache manipulation from this context. Clear req->r_locked_dir since
it's clearly not safe to do that.

What we really want to know with d_revalidate is whether the dentry
still points to the same inode. ceph_fill_trace installs a pointer to
the inode in req->r_target_inode, so we can just compare that to
d_inode(dentry) to see if it's the same one after the lookup.

Also, since we aren't generally interested in the parent here, we can
switch to using a GETATTR to hint that to the MDS, which also means that
we only need to reserve one cap.

Finally, just remove the d_unhashed check. That's really outside the
purview of a filesystem's d_revalidate. If the thing became unhashed
while we're checking it, then that's up to the VFS to handle anyway.

Fixes: 200fd27c ("ceph: use lookup request to revalidate dentry")
Link: http://tracker.ceph.com/issues/18041Reported-by: Donatas Abraitis <donatas.abraitis@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/dir.c

@@ -1261,26 +1261,30 @@ static int ceph_d_revalidate(struct dentry *dentry, unsigned int flags)
 			return -ECHILD;
 
 		op = ceph_snap(dir) == CEPH_SNAPDIR ?
-			CEPH_MDS_OP_LOOKUPSNAP : CEPH_MDS_OP_LOOKUP;
+			CEPH_MDS_OP_LOOKUPSNAP : CEPH_MDS_OP_GETATTR;
 		req = ceph_mdsc_create_request(mdsc, op, USE_ANY_MDS);
 		if (!IS_ERR(req)) {
 			req->r_dentry = dget(dentry);
-			req->r_num_caps = 2;
+			req->r_num_caps = op == CEPH_MDS_OP_GETATTR ? 1 : 2;
 
 			mask = CEPH_STAT_CAP_INODE | CEPH_CAP_AUTH_SHARED;
 			if (ceph_security_xattr_wanted(dir))
 				mask |= CEPH_CAP_XATTR_SHARED;
 			req->r_args.getattr.mask = mask;
 
-			req->r_locked_dir = dir;
 			err = ceph_mdsc_do_request(mdsc, NULL, req);
-			if (err == 0 || err == -ENOENT) {
-				if (dentry == req->r_dentry) {
-					valid = !d_unhashed(dentry);
-				} else {
-					d_invalidate(req->r_dentry);
-					err = -EAGAIN;
-				}
+			switch (err) {
+			case 0:
+				if (d_really_is_positive(dentry) &&
+				    d_inode(dentry) == req->r_target_inode)
+					valid = 1;
+				break;
+			case -ENOENT:
+				if (d_really_is_negative(dentry))
+					valid = 1;
+				/* Fallthrough */
+			default:
+				break;
 			}
 			ceph_mdsc_put_request(req);
 			dout("d_revalidate %p lookup result=%d\n",