On Thu, Jun 1, 2017 at 6:22 PM, Arnd Bergmann [off-list ref] wrote:

On Thu, Jun 1, 2017 at 11:56 AM, Yan, Zheng [off-list ref] wrote:

quoted

On Sat, Apr 8, 2017 at 8:57 AM, Deepa Dinamani [off-list ref] wrote:

quoted

quoted

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 517838b..77204da 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c

@@ -1922,7 +1922,7 @@ static void rbd_osd_req_format_write(struct rbd_obj_request *obj_request)
 {
        struct ceph_osd_request *osd_req = obj_request->osd_req;

-       osd_req->r_mtime = CURRENT_TIME;
+       ktime_get_real_ts(&osd_req->r_mtime);
        osd_req->r_data_offset = obj_request->offset;
 }

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index c681762..1d3fa90 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c

@@ -1666,6 +1666,7 @@ struct ceph_mds_request *
 ceph_mdsc_create_request(struct ceph_mds_client *mdsc, int op, int mode)
 {
        struct ceph_mds_request *req = kzalloc(sizeof(*req), GFP_NOFS);
+       struct timespec ts;

        if (!req)
                return ERR_PTR(-ENOMEM);

@@ -1684,7 +1685,8 @@ ceph_mdsc_create_request(struct ceph_mds_client *mdsc, int op, int mode)
        init_completion(&req->r_safe_completion);
        INIT_LIST_HEAD(&req->r_unsafe_item);

-       req->r_stamp = current_fs_time(mdsc->fsc->sb);
+       ktime_get_real_ts(&ts);
+       req->r_stamp = timespec_trunc(ts, mdsc->fsc->sb->s_time_gran);

This change causes our kernel_untar_tar test case to fail (inode's
ctime goes back). The reason is that there is time drift between the
time stamps got by  ktime_get_real_ts() and current_time(). We need to
revert this change until current_time() uses ktime_get_real_ts()
internally.

Hmm, the change was not supposed to have a user-visible effect, so
something has gone wrong, but I don't immediately see how it
relates to what you observe.

ktime_get_real_ts() and current_time() use the same time base, there
is no drift, but there is a difference in resolution, as the latter uses
the time stamp of the last jiffies update, which may be up to one jiffy
(10ms) behind the exact time we put in the request stamps here.

It happens in following sequence of events

1. create a new file, the inode's ctime is set to ktime_get_real_ts()
2. chmod the new file, the inode's ctime is set to current_time().

Inode's ctime goes back when current_time() is behind ktime_get_real_ts().

Regards
Yan, Zheng

Do you still see problems if you use current_kernel_time() instead of
ktime_get_real_ts()?

        Arnd