linux-kernel - nfs+tcp boot failures on linuxnext-20180924 from switch tcp_clock_ns to CLOCK

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Date:   Thu, 27 Sep 2018 01:15:37 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: nfs+tcp boot failures on linuxnext-20180924 from switch tcp_clock_ns
 to CLOCK_TAI

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.

--
Regards,
Leonard