From: Thomas Gleixner <tglx@linutronix.de>
To: paulmck@kernel.org
Cc: Feng Tang <feng.tang@intel.com>,
kernel test robot <oliver.sang@intel.com>,
0day robot <lkp@intel.com>, John Stultz <john.stultz@linaro.org>,
Stephen Boyd <sboyd@kernel.org>, Jonathan Corbet <corbet@lwn.net>,
Mark Rutland <Mark.Rutland@arm.com>,
Marc Zyngier <maz@kernel.org>, Andi Kleen <ak@linux.intel.com>,
Xing Zhengjun <zhengjun.xing@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
lkp@lists.01.org, kernel-team@fb.com, neeraju@codeaurora.org,
zhengjun.xing@intel.com, x86@kernel.org,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [clocksource] 8c30ace35d: WARNING:at_kernel/time/clocksource.c:#clocksource_watchdog
Date: Thu, 29 Apr 2021 19:30:20 +0200 [thread overview]
Message-ID: <87lf91f177.ffs@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20210429142641.GU975577@paulmck-ThinkPad-P17-Gen-1>
Paul,
On Thu, Apr 29 2021 at 07:26, Paul E. McKenney wrote:
> On Thu, Apr 29, 2021 at 10:27:09AM +0200, Thomas Gleixner wrote:
>> > Or are you saying that the checks should be in the host OS rather than
>> > in the guests?
>>
>> Yes. That's where it belongs. The host has to make sure that TSC is usable
>> otherwise it should tell the guest not to use it. Anything else is
>> wishful thinking and never reliable.
>
> Thank you for the confirmation. I will look into this.
So the guest might need at least some basic sanity checking unless we
declare that hypervisors are always working correctly :)
Which is admittedly more likely than making the same assumption about
BIOS and hardware.
>> > In addition, breakage due to age and environmentals is possible, and if
>> > you have enough hardware, probable. In which case it would be good to
>> > get a notification so that the system in question can be dealt with.
>>
>> Are you trying to find a problem for a solution again?
>
> We really do see this thing trigger. > I am trying to get rid of one
> class of false positives that might be afflicting us. Along the way,
> I am thinking aloud about what might be the cause of any remaining
> skew reports that might trigger in the future.
Fair enough. Admittedly this has at least entertainment value :)
>> Well, you might then also build safety nets for interrupts, exceptions
>> and if you go fully paranoid for every single CPU instruction. :)
>
> Fair, and I doubt that looking at failure data across a large fleet of
> systems has done anything to reduce my level of paranoia. ;-)
You should have known better than opening Pandoras box.
>> Sure. If you have a seperate module then you can add module params to it
>> obviously. But you don't need any of the muck in the actual watchdog
>> code because the watchdog::read() function in that module will simply
>> handle the delay injection. Hmm?
>
> OK, first let me make sure I understand what you are suggesting.
>
> The idea is to leave the watchdog code in kernel/time/clocksource.c,
> but to move the fault injection into kernel/time/clocksourcefault.c or
> some such. In this new file, new clocksource structures are created that
> use some existing timebase/clocksource under the covers. These then
> inject delays based on module parameters (one senstive to CPU number,
> the other unconditional). They register these clocksources using the
> normal interfaces, and verify that they are eventually marked unstable
> when the fault-injection parameters warrant it. This is combined with
> the usual checking of the console log.
>
> Or am I missing your point?
That's what I meant.
Thanks,
tglx
next prev parent reply other threads:[~2021-04-29 17:30 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-25 22:45 [PATCH v10 clocksource 0/7] Do not mark clocks unstable due to delays for v5.13 Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 1/7] clocksource: Provide module parameters to inject delays in watchdog Paul E. McKenney
2021-04-26 4:07 ` Andi Kleen
2021-04-26 7:13 ` Thomas Gleixner
2021-04-26 15:28 ` Paul E. McKenney
2021-04-26 16:00 ` Andi Kleen
2021-04-26 16:14 ` Paul E. McKenney
2021-04-26 17:56 ` Andi Kleen
2021-04-26 18:24 ` Paul E. McKenney
2021-04-28 4:49 ` Luming Yu
2021-04-28 13:57 ` Paul E. McKenney
2021-04-28 14:24 ` Luming Yu
2021-04-28 14:37 ` Thomas Gleixner
2021-04-25 22:47 ` [PATCH v10 clocksource 2/7] clocksource: Retry clock read if long delays detected Paul E. McKenney
2021-04-27 1:44 ` Feng Tang
2021-04-25 22:47 ` [PATCH v10 clocksource 3/7] clocksource: Check per-CPU clock synchronization when marked unstable Paul E. McKenney
2021-04-26 4:12 ` Andi Kleen
2021-04-26 7:16 ` Thomas Gleixner
2021-04-25 22:47 ` [PATCH v10 clocksource 4/7] clocksource: Provide a module parameter to fuzz per-CPU clock checking Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 5/7] clocksource: Limit number of CPUs checked for clock synchronization Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 6/7] clocksource: Forgive tsc_early pre-calibration drift Paul E. McKenney
2021-04-26 15:01 ` Feng Tang
2021-04-26 15:25 ` Paul E. McKenney
2021-04-26 15:36 ` Feng Tang
2021-04-26 18:26 ` Paul E. McKenney
2021-04-27 1:13 ` Feng Tang
2021-04-27 3:46 ` Paul E. McKenney
2021-04-27 4:16 ` Feng Tang
2021-04-26 15:28 ` Thomas Gleixner
2021-04-27 21:03 ` Thomas Gleixner
2021-04-27 7:27 ` [clocksource] 8c30ace35d: WARNING:at_kernel/time/clocksource.c:#clocksource_watchdog kernel test robot
2021-04-27 8:45 ` Feng Tang
2021-04-27 13:37 ` Paul E. McKenney
2021-04-27 17:50 ` Paul E. McKenney
2021-04-27 21:09 ` Thomas Gleixner
2021-04-28 1:48 ` Paul E. McKenney
2021-04-28 10:14 ` Thomas Gleixner
2021-04-28 18:31 ` Paul E. McKenney
2021-04-28 13:34 ` Thomas Gleixner
2021-04-28 15:39 ` Peter Zijlstra
2021-04-28 17:00 ` Thomas Gleixner
2021-04-29 7:38 ` Feng Tang
2021-04-28 18:31 ` Paul E. McKenney
2021-04-29 8:27 ` Thomas Gleixner
2021-04-29 14:26 ` Paul E. McKenney
2021-04-29 17:30 ` Thomas Gleixner [this message]
2021-04-29 23:04 ` Andi Kleen
2021-04-30 0:24 ` Paul E. McKenney
2021-04-30 0:59 ` Paul E. McKenney
2021-04-30 5:08 ` Paul E. McKenney
2021-04-25 22:47 ` [PATCH v9 clocksource 6/6] clocksource: Reduce WATCHDOG_THRESHOLD Paul E. McKenney
2021-04-25 22:47 ` [PATCH v10 clocksource 7/7] " Paul E. McKenney
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