Re: infinite loop in read_hpet from ktime_get_boot_fast_ns

From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Clemens Ladisch <clemens@ladisch.de>,
	Sultan Alsawaf <sultan@kerneltoast.com>,
	Waiman Long <longman@redhat.com>, X86 ML <x86@kernel.org>
Subject: Re: infinite loop in read_hpet from ktime_get_boot_fast_ns
Date: Thu, 13 Jun 2019 18:34:22 +0200	[thread overview]
Message-ID: <CAHmME9q1ihF617=Gjw9k9BK7OC9Ghnzfnfi6LfvJ8DG+vrQOqA@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1906131822300.1791@nanos.tec.linutronix.de>

On Thu, Jun 13, 2019 at 6:26 PM Thomas Gleixner <tglx@linutronix.de> wrote:
> That does not make sense. The coarse time getters use
> tk->tkr_mono.base. base is updated every tick (or if the machine is
> completely idle right when the first CPU wakes up again).

Sense or not, it seems to be happening, at least on 5.2-rc4:

int __init mod_init(void)
{
      for (;;) {
              pr_err("%llu %llu %llu\n", get_jiffies_64(),
ktime_get_coarse_boottime(), local_clock());
              msleep(200);
      }
      return 0;
}

[    0.308166] wireguard: 4294892358 270211253 308165785
[    0.512931] wireguard: 4294892410 270211253 512926052
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[    0.928995] wireguard: 4294892514 270211253 928990019
[    1.137011] wireguard: 4294892566 270211253 1137005585
[    1.344948] wireguard: 4294892618 1270211253 1344943311
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[    1.760963] wireguard: 4294892722 1270211253 1760957241
[    1.969092] wireguard: 4294892774 1270211253 1969087174
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[    3.008895] wireguard: 4294893034 2270211253 3008892169
[    3.216956] wireguard: 4294893086 2270211253 3216951160
[    3.424965] wireguard: 4294893138 3270211253 3424960158
[    3.632942] wireguard: 4294893190 3270211253 3632937133
[    3.840947] wireguard: 4294893242 3270211253 3840942470
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[    4.257078] wireguard: 4294893346 3270211253 4257072850
[    4.464943] wireguard: 4294893398 4270211253 4464938724
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[    5.712963] wireguard: 4294893710 5270211253 5712957452
[    5.920949] wireguard: 4294893762 5270211253 5920944292
[    6.128959] wireguard: 4294893814 5270211253 6128954684
[    6.336968] wireguard: 4294893866 6270211253 6336962979
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[    6.752963] wireguard: 4294893970 6270211253 6752958001
[    6.961008] wireguard: 4294894022 6270211253 6961003309
[    7.169073] wireguard: 4294894074 6270211253 7169068202
[    7.376936] wireguard: 4294894126 7270211253 7376931429
[    7.585022] wireguard: 4294894178 7270211253 7585016996
[    7.793004] wireguard: 4294894230 7270211253 7792999324
[    8.000953] wireguard: 4294894282 7270211253 8000947668
[    8.208949] wireguard: 4294894334 7270211253 8208943630
[    8.417090] wireguard: 4294894386 8270211253 8417085802
[    8.625071] wireguard: 4294894438 8270211253 8625066012
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[    9.041032] wireguard: 4294894542 8270211253 9041027362
[    9.248948] wireguard: 4294894594 8270211253 9248943016
[    9.456968] wireguard: 4294894646 9270211253 9456963019
[    9.664955] wireguard: 4294894698 9270211253 9664950178
[    9.872935] wireguard: 4294894750 9270211253 9872929704