ceph: skip updating 'wanted' caps if caps are already issued

When reading cached inode that already has Fscr caps, this can avoid
two cap messages (one updats 'wanted' caps, one clears 'wanted' caps).
Signed-off-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -1973,8 +1973,7 @@ void ceph_check_caps(struct ceph_inode_info *ci, int flags,
 			goto ack;
 
 		/* things we might delay */
-		if ((cap->issued & ~retain) == 0 &&
-		    cap->mds_wanted == want)
+		if ((cap->issued & ~retain) == 0)
 			continue;     /* nope, all good */
 
 		if (no_delay)
@@ -3051,7 +3050,8 @@ static void handle_cap_grant(struct inode *inode,
 	int used, wanted, dirty;
 	u64 size = le64_to_cpu(grant->size);
 	u64 max_size = le64_to_cpu(grant->max_size);
-	int check_caps = 0;
+	unsigned char check_caps = 0;
+	bool was_stale = cap->cap_gen < session->s_cap_gen;
 	bool wake = false;
 	bool writeback = false;
 	bool queue_trunc = false;
@@ -3203,13 +3203,20 @@ static void handle_cap_grant(struct inode *inode,
 	     ceph_cap_string(wanted),
 	     ceph_cap_string(used),
 	     ceph_cap_string(dirty));
-	if (wanted != le32_to_cpu(grant->wanted)) {
-		dout("mds wanted %s -> %s\n",
-		     ceph_cap_string(le32_to_cpu(grant->wanted)),
-		     ceph_cap_string(wanted));
-		/* imported cap may not have correct mds_wanted */
-		if (le32_to_cpu(grant->op) == CEPH_CAP_OP_IMPORT)
-			check_caps = 1;
+
+	if ((was_stale || le32_to_cpu(grant->op) == CEPH_CAP_OP_IMPORT) &&
+	    (wanted & ~(cap->mds_wanted | newcaps))) {
+		/*
+		 * If mds is importing cap, prior cap messages that update
+		 * 'wanted' may get dropped by mds (migrate seq mismatch).
+		 *
+		 * We don't send cap message to update 'wanted' if what we
+		 * want are already issued. If mds revokes caps, cap message
+		 * that releases caps also tells mds what we want. But if
+		 * caps got revoked by mds forcedly (session stale). We may
+		 * haven't told mds what we want.
+		 */
+		check_caps = 1;
 	}
 
 	/* revocation, grant, or no-op? */