linux-kernel - Re: UML time-travel warning from __run

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Message-ID: <877d86m978.ffs@tglx>
Date:   Sun, 03 Apr 2022 18:18:51 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Johannes Berg <johannes@...solutions.net>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     linux-um@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Anna-Maria Gleixner <anna-maria@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: Re: UML time-travel warning from __run_timers

On Sat, Apr 02 2022 at 16:09, Johannes Berg wrote:
> At init, we get
>
> init_timer_cpu(0) base 0 clk=0xffff8ad0, next_expiry=0x13fff8acf
> init_timer_cpu(0) base 1 clk=0xffff8ad0, next_expiry=0x13fff8acf
>
> which makes sense, jiffies is set up to wrap very quickly after boot.
>
> The warning triggers when we have jiffies=0x13fff9600, so it's just
> after the "next_expiry", so in this code:

which does not make sense. If next_expiry is 0x13fff8acf and jiffies
advanced to 0x13fff9600 when the warning triggered, then either it
missed to expire the timer at 0x13fff8acf or it failed to recalculate
next_expiry.

Could you enable all [hr]timer tracepoints on the kernel command line,
set panic on warn and ftrace_dump_on_oops which should spill out the
tracebuffer on the console and provide the output. That should at least
give us an hint what's going on.

Thanks,

        tglx