ceph: improving efficiency of syncfs

write_inode() could be called variety of reasons, in the case of syncfs(2)
there is no need to wait for flush getting completed in write_inode(),
->sync_fs is for guaranteeing flush completion for all inodes at that point.
Signed-off-by: NChengguang Xu <cgxu519@icloud.com>
Reviewed-by: N"Yan, Zheng" <zyan@redhat.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

fs/ceph/caps.c

@@ -2207,7 +2207,7 @@ int ceph_write_inode(struct inode *inode, struct writeback_control *wbc)
 	u64 flush_tid;
 	int err = 0;
 	int dirty;
-	int wait = wbc->sync_mode == WB_SYNC_ALL;
+	int wait = (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync);
 
 	dout("write_inode %p wait=%d\n", inode, wait);
 	if (wait) {