ceph: use empty snap context for uninline_data and get_pool_perm

Cached_context in ceph_snap_realm is directly accessed by
uninline_data() and get_pool_perm(). This is racy in theory.
both uninline_data() and get_pool_perm() do not modify existing
object, they only create new object. So we can pass the empty
snap context to them.  Unlike cached_context in ceph_snap_realm,
we do not need to protect the empty snap context.

Signed-off-by: Yan, Zheng <zyan@redhat.com>
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index b960277..ccc4325 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -1510,8 +1510,7 @@
 				    ceph_vino(inode), 0, &len, 0, 1,
 				    CEPH_OSD_OP_CREATE,
 				    CEPH_OSD_FLAG_ONDISK | CEPH_OSD_FLAG_WRITE,
-				    ci->i_snap_realm->cached_context,
-				    0, 0, false);
+				    ceph_empty_snapc, 0, 0, false);
 	if (IS_ERR(req)) {
 		err = PTR_ERR(req);
 		goto out;
@@ -1529,7 +1528,7 @@
 				    ceph_vino(inode), 0, &len, 1, 3,
 				    CEPH_OSD_OP_WRITE,
 				    CEPH_OSD_FLAG_ONDISK | CEPH_OSD_FLAG_WRITE,
-				    ci->i_snap_realm->cached_context,
+				    ceph_empty_snapc,
 				    ci->i_truncate_seq, ci->i_truncate_size,
 				    false);
 	if (IS_ERR(req)) {
@@ -1653,7 +1652,7 @@
 	}
 
 	rd_req = ceph_osdc_alloc_request(&fsc->client->osdc,
-					 ci->i_snap_realm->cached_context,
+					 ceph_empty_snapc,
 					 1, false, GFP_NOFS);
 	if (!rd_req) {
 		err = -ENOMEM;
@@ -1668,7 +1667,7 @@
 	rd_req->r_base_oid.name_len = strlen(rd_req->r_base_oid.name);
 
 	wr_req = ceph_osdc_alloc_request(&fsc->client->osdc,
-					 ci->i_snap_realm->cached_context,
+					 ceph_empty_snapc,
 					 1, false, GFP_NOFS);
 	if (!wr_req) {
 		err = -ENOMEM;