linux-kernel - Re: infinite loop in read_hpet from ktime_get_boot_fast

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Message-ID: <CAHmME9oNr9VUiDqRHsrSg+oFmsoJfTv3yGTzjDsokUX7ZYv0JQ@mail.gmail.com>
Date:   Thu, 13 Jun 2019 18:41:36 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Clemens Ladisch <clemens@...isch.de>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Waiman Long <longman@...hat.com>, X86 ML <x86@...nel.org>
Subject: Re: infinite loop in read_hpet from ktime_get_boot_fast_ns

Or in case that's not clear enough:

int __init mod_init(void)
{
  u64 j1 = 0, j2, k1 = 0, k2, l1 = 0, l2;
  for (;;) {
    j2 = jiffies64_to_nsecs(get_jiffies_64());
    k2 = ktime_get_coarse_boottime();
    l2 = local_clock();
    pr_err("%llu %llu %llu\n", j2 - j1, k2 - k1, l2 - l1);
    j1 = j2;
    k1 = k2;
    l1 = l2;
    msleep(200);
  }
  return 0;
}

[    0.289469] wireguard: 17179569424000000 18446744073155127569 289468886
[    0.495002] wireguard: 208000000 1000000000 205528400
[    0.702857] wireguard: 208000000 0 207855129
[    0.910836] wireguard: 208000000 0 207979087
[    1.118871] wireguard: 208000000 0 208034819
[    1.326964] wireguard: 208000000 0 208093122
[    1.534941] wireguard: 208000000 1000000000 207976614
[    1.742868] wireguard: 208000000 0 207927167
[    1.950877] wireguard: 208000000 0 208009538
[    2.158865] wireguard: 208000000 0 207987922
[    2.367012] wireguard: 208000000 0 208146016
[    2.574931] wireguard: 208000000 1000000000 207918184
[    2.782871] wireguard: 208000000 0 207939645
[    2.991017] wireguard: 208000000 0 208148426
[    3.198943] wireguard: 208000000 0 207925281
[    3.406959] wireguard: 208000000 0 208014262
[    3.614892] wireguard: 208000000 1000000000 207934524
[    3.822869] wireguard: 208000000 0 207976970
[    4.030994] wireguard: 208000000 0 208125835
[    4.238792] wireguard: 208000000 0 207800186
[    4.446853] wireguard: 208000000 0 208056350
[    4.654978] wireguard: 208000000 1000000000 208126753
[    4.862801] wireguard: 208000000 0 207822955
[    5.070999] wireguard: 208000000 0 208198517
[    5.278818] wireguard: 208000000 0 207820902
[    5.486879] wireguard: 208000000 1000000000 208059285
[    5.694959] wireguard: 208000000 0 208066514
[    5.903011] wireguard: 208000000 0 208065258
[    6.111015] wireguard: 208000000 0 208004056
[    6.318856] wireguard: 208000000 0 207841271