From: Xiubo Li <xiubli@redhat.com>
Date: Thu, 11 Aug 2022 13:00:53 +0800
Subject: ceph: no need to wait for transition RDCACHE|RD -> RD
Git-commit: 7c3ea9870e09e193981695dd67c37a1a2b6d600b
Patch-mainline: v6.1-rc1
References: jsc#SES-1880

For write when trying to get the Fwb caps we need to keep waiting
on transition from WRBUFFER|WR -> WR to avoid a new WR sync write
from going before a prior buffered writeback happens.

While for read there is no need to wait on transition from
RDCACHE|RD -> RD, and we can just exclude the revoking caps and
force to sync read.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Acked-by: Luis Henriques <lhenriques@suse.de>
---
 fs/ceph/caps.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ceph/caps.c b/fs/ceph/caps.c
index 0ddd91eadbce..0dc1251c3c6d 100644
--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -2760,13 +2760,17 @@ static int try_get_cap_refs(struct inode *inode, int need, int want,
 		 * on transition from wanted -> needed caps.  This is needed
 		 * for WRBUFFER|WR -> WR to avoid a new WR sync write from
 		 * going before a prior buffered writeback happens.
+		 *
+		 * For RDCACHE|RD -> RD, there is not need to wait and we can
+		 * just exclude the revoking caps and force to sync read.
 		 */
 		int not = want & ~(have & need);
 		int revoking = implemented & ~have;
+		int exclude = revoking & not;
 		dout("get_cap_refs %p have %s but not %s (revoking %s)\n",
 		     inode, ceph_cap_string(have), ceph_cap_string(not),
 		     ceph_cap_string(revoking));
-		if ((revoking & not) == 0) {
+		if (!exclude || !(exclude & CEPH_CAP_FILE_BUFFER)) {
 			if (!snap_rwsem_locked &&
 			    !ci->i_head_snapc &&
 			    (need & CEPH_CAP_FILE_WR)) {
@@ -2788,7 +2792,7 @@ static int try_get_cap_refs(struct inode *inode, int need, int want,
 				snap_rwsem_locked = true;
 			}
 			if ((have & want) == want)
-				*got = need | want;
+				*got = need | (want & ~exclude);
 			else
 				*got = need;
 			ceph_take_cap_refs(ci, *got, true);