On 09/26/2018 06:15 PM, Leonard Crestez wrote:

Hello,
 
It seems that after commit 72b0094f9182 ("tcp: switch tcp_clock_ns() to
CLOCK_TAI base") some systems that use nfs over tcp fail to boot. The
last line printed in the log is from systemd:
 
[    7.232579] systemd[1]: System time before build time, advancing clock.
 
Superficially it looks like very large clock discontinuities now break
TCP. Maybe boottime could avoid such issues?
 
I didn't find similar reports anywhere else. The machines I’m seeing
this are all 32bit arm imx (this shouldn’t matter) and it seems their
RTC isn’t properly setup so they boot with realtime set to unix zero,
then a ~50 years jump happens when systemd starts up. This is the
likely trigger for this issue.
 

Thanks for the report.

It is annoying, because SCM_TXTIME and net/sched/sch_etf.c are using CLOCK_TAI,
so it means that if we convert TCP (and net/sched/sch_fq.c) back to ktime_get_ns(),
we will have to differentiate in skbs the clock base.

This has been discussed in the past (When ETF was merged in 4.19) and we chose
to use a common clock base.