linux-kernel - Re: [PATCH] net: ceph: Use CLOCK_MONOTONIC ktime_get

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Date:   Sat, 19 Jun 2021 06:51:08 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Yejune Deng <yejune.deng@...il.com>, idryomov@...il.com,
        davem@...emloft.net, kuba@...nel.org
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: ceph: Use CLOCK_MONOTONIC ktime_get_ts64()

On Fri, 2021-06-18 at 22:27 +0800, Yejune Deng wrote:
> The Documentation/core-api/timekeeping.rst recommend that we should use
> monotonic time ktime_get_ts64(), to avoid glitches with a concurrent
> settimeofday().
> 
> Signed-off-by: Yejune Deng <yejune.deng@...il.com>
> ---
>  net/ceph/messenger.c    | 2 +-
>  net/ceph/messenger_v1.c | 2 +-
>  net/ceph/messenger_v2.c | 2 +-
>  net/ceph/osd_client.c   | 4 ++--
>  4 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/net/ceph/messenger.c b/net/ceph/messenger.c
> index 57d043b..2d07ab5 100644
> --- a/net/ceph/messenger.c
> +++ b/net/ceph/messenger.c
> @@ -1809,7 +1809,7 @@ bool ceph_con_keepalive_expired(struct ceph_connection *con,
>  	    (con->peer_features & CEPH_FEATURE_MSGR_KEEPALIVE2)) {
>  		struct timespec64 now;
>  		struct timespec64 ts;
> -		ktime_get_real_ts64(&now);
> +		ktime_get_ts64(&now);
>  		jiffies_to_timespec64(interval, &ts);
>  		ts = timespec64_add(con->last_keepalive_ack, ts);
>  		return timespec64_compare(&now, &ts) >= 0;
> diff --git a/net/ceph/messenger_v1.c b/net/ceph/messenger_v1.c
> index 2cb5ffd..2ec7b1d 100644
> --- a/net/ceph/messenger_v1.c
> +++ b/net/ceph/messenger_v1.c
> @@ -310,7 +310,7 @@ static void prepare_write_keepalive(struct ceph_connection *con)
>  	if (con->peer_features & CEPH_FEATURE_MSGR_KEEPALIVE2) {
>  		struct timespec64 now;
>  
> -		ktime_get_real_ts64(&now);
> +		ktime_get_ts64(&now);
>  		con_out_kvec_add(con, sizeof(tag_keepalive2), &tag_keepalive2);
>  		ceph_encode_timespec64(&con->v1.out_temp_keepalive2, &now);
>  		con_out_kvec_add(con, sizeof(con->v1.out_temp_keepalive2),
> diff --git a/net/ceph/messenger_v2.c b/net/ceph/messenger_v2.c
> index cc40ce4..2125e77 100644
> --- a/net/ceph/messenger_v2.c
> +++ b/net/ceph/messenger_v2.c
> @@ -1439,7 +1439,7 @@ static int prepare_keepalive2(struct ceph_connection *con)
>  	struct ceph_timespec *ts = CTRL_BODY(con->v2.out_buf);
>  	struct timespec64 now;
>  
> -	ktime_get_real_ts64(&now);
> +	ktime_get_ts64(&now);
>  	dout("%s con %p timestamp %lld.%09ld\n", __func__, con, now.tv_sec,
>  	     now.tv_nsec);
>  
> diff --git a/net/ceph/osd_client.c b/net/ceph/osd_client.c
> index ff8624a..5192a8a 100644
> --- a/net/ceph/osd_client.c
> +++ b/net/ceph/osd_client.c
> @@ -4717,7 +4717,7 @@ ceph_osdc_watch(struct ceph_osd_client *osdc,
>  	ceph_oid_copy(&lreq->t.base_oid, oid);
>  	ceph_oloc_copy(&lreq->t.base_oloc, oloc);
>  	lreq->t.flags = CEPH_OSD_FLAG_WRITE;
> -	ktime_get_real_ts64(&lreq->mtime);
> +	ktime_get_ts64(&lreq->mtime);
>  
>  	lreq->reg_req = alloc_watch_request(lreq, CEPH_OSD_WATCH_OP_WATCH);
>  	if (!lreq->reg_req) {
> @@ -4767,7 +4767,7 @@ int ceph_osdc_unwatch(struct ceph_osd_client *osdc,
>  	ceph_oid_copy(&req->r_base_oid, &lreq->t.base_oid);
>  	ceph_oloc_copy(&req->r_base_oloc, &lreq->t.base_oloc);
>  	req->r_flags = CEPH_OSD_FLAG_WRITE;
> -	ktime_get_real_ts64(&req->r_mtime);
> +	ktime_get_ts64(&req->r_mtime);
>  	osd_req_op_watch_init(req, 0, lreq->linger_id,
>  			      CEPH_OSD_WATCH_OP_UNWATCH);
>  

I think this is OK. Most of these timestamps get marshalled onto the
wire to use as identifiers. Those are almost certainly better off with
CLOCK_MONOTONIC since you could have a clock jump that caused you to
send (e.g.) 2 keepalives with the same timestamp otherwise.

Reviewed-by: Jeff Layton <jlayton@...nel.org>