From: "Yan, Zheng" <zyan@redhat.com>
Date: Thu, 22 Nov 2018 15:26:01 +0800
Subject: ceph: skip updating 'wanted' caps if caps are already issued
Git-commit: fdac94fab7995ebc52ff9c5b6247133c67a7564a
Patch-mainline: v5.0-rc1
References: bsc#1122215

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>
Acked-by: Luis Henriques <lhenriques@suse.com>
---
 fs/ceph/caps.c |   27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -1970,8 +1970,7 @@ retry_locked:
 			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)
@@ -3047,7 +3046,8 @@ static void handle_cap_grant(struct inod
 	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;
@@ -3199,13 +3199,20 @@ static void handle_cap_grant(struct inod
 	     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? */