staging/lustre/ost: Ensure dirty flushed on fiemap ioctl

Data corruption is possible if cp(coreutils) uses FIEMAP to obtain
data holes in shared file, since there could be dirty cache on
other clients which hasn't been flushed back.

To ensure all the dirty on remote clients being flushed back on
fiemap ioctl, we'd acquire ldlm lock on server side for fiemap,
unless the local client (which invoke fiemap) has cached lock.

[picked osc part for upstream kernel submission]
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3219
Xyratex-bug-id: MRP-1001
Lustre-change: http://review.whamcloud.com/6127Signed-off-by: Artem Blagodarenko <artem_blagodarenko@xyratex.com>
Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/osc/osc_request.c

@@ -3062,15 +3062,52 @@ static int osc_get_info(const struct lu_env *env, struct obd_export *exp,
 		ptlrpc_req_finished(req);
 		RETURN(rc);
 	} else if (KEY_IS(KEY_FIEMAP)) {
-		struct ptlrpc_request *req;
-		struct ll_user_fiemap *reply;
-		char *tmp;
-		int rc;
+		struct ll_fiemap_info_key *fm_key =
+				(struct ll_fiemap_info_key *)key;
+		struct ldlm_res_id	 res_id;
+		ldlm_policy_data_t	 policy;
+		struct lustre_handle	 lockh;
+		ldlm_mode_t		 mode = 0;
+		struct ptlrpc_request	*req;
+		struct ll_user_fiemap	*reply;
+		char			*tmp;
+		int			 rc;
+
+		if (!(fm_key->fiemap.fm_flags & FIEMAP_FLAG_SYNC))
+			goto skip_locking;
+
+		policy.l_extent.start = fm_key->fiemap.fm_start &
+						CFS_PAGE_MASK;
+
+		if (OBD_OBJECT_EOF - fm_key->fiemap.fm_length <=
+		    fm_key->fiemap.fm_start + PAGE_CACHE_SIZE - 1)
+			policy.l_extent.end = OBD_OBJECT_EOF;
+		else
+			policy.l_extent.end = (fm_key->fiemap.fm_start +
+				fm_key->fiemap.fm_length +
+				PAGE_CACHE_SIZE - 1) & CFS_PAGE_MASK;
+
+		ostid_build_res_name(&fm_key->oa.o_oi, &res_id);
+		mode = ldlm_lock_match(exp->exp_obd->obd_namespace,
+				       LDLM_FL_BLOCK_GRANTED |
+				       LDLM_FL_LVB_READY,
+				       &res_id, LDLM_EXTENT, &policy,
+				       LCK_PR | LCK_PW, &lockh, 0);
+		if (mode) { /* lock is cached on client */
+			if (mode != LCK_PR) {
+				ldlm_lock_addref(&lockh, LCK_PR);
+				ldlm_lock_decref(&lockh, LCK_PW);
+			}
+		} else { /* no cached lock, needs acquire lock on server side */
+			fm_key->oa.o_valid |= OBD_MD_FLFLAGS;
+			fm_key->oa.o_flags |= OBD_FL_SRVLOCK;
+		}
 
+skip_locking:
 		req = ptlrpc_request_alloc(class_exp2cliimp(exp),
 					   &RQF_OST_GET_INFO_FIEMAP);
 		if (req == NULL)
-			RETURN(-ENOMEM);
+			GOTO(drop_lock, rc = -ENOMEM);
 
 		req_capsule_set_size(&req->rq_pill, &RMF_FIEMAP_KEY,
 				     RCL_CLIENT, keylen);
@@ -3082,7 +3119,7 @@ static int osc_get_info(const struct lu_env *env, struct obd_export *exp,
 		rc = ptlrpc_request_pack(req, LUSTRE_OST_VERSION, OST_GET_INFO);
 		if (rc) {
 			ptlrpc_request_free(req);
-			RETURN(rc);
+			GOTO(drop_lock, rc);
 		}
 
 		tmp = req_capsule_client_get(&req->rq_pill, &RMF_FIEMAP_KEY);
@@ -3093,16 +3130,18 @@ static int osc_get_info(const struct lu_env *env, struct obd_export *exp,
 		ptlrpc_request_set_replen(req);
 		rc = ptlrpc_queue_wait(req);
 		if (rc)
-			GOTO(out1, rc);
+			GOTO(fini_req, rc);
 
 		reply = req_capsule_server_get(&req->rq_pill, &RMF_FIEMAP_VAL);
 		if (reply == NULL)
-			GOTO(out1, rc = -EPROTO);
+			GOTO(fini_req, rc = -EPROTO);
 
 		memcpy(val, reply, *vallen);
-	out1:
+fini_req:
 		ptlrpc_req_finished(req);
-
+drop_lock:
+		if (mode)
+			ldlm_lock_decref(&lockh, LCK_PR);
 		RETURN(rc);
 	}