linux-kernel - Re: [PATCH v7 clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable

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Message-ID: <87o8ejz1c9.ffs@nanos.tec.linutronix.de>
Date:   Mon, 12 Apr 2021 22:37:10 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     paulmck@...nel.org
Cc:     linux-kernel@...r.kernel.org, john.stultz@...aro.org,
        sboyd@...nel.org, corbet@....net, Mark.Rutland@....com,
        maz@...nel.org, kernel-team@...com, neeraju@...eaurora.org,
        ak@...ux.intel.com
Subject: Re: [PATCH v7 clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable

On Mon, Apr 12 2021 at 12:57, Paul E. McKenney wrote:
> On Mon, Apr 12, 2021 at 08:54:03PM +0200, Thomas Gleixner wrote:
>> > I will send a new series out later today, Pacific Time.
>> 
>> Can you do me a favour and send it standalone and not as yet another
>> reply to this existing thread maze. A trivial lore link to the previous
>> version gives enough context.
>
> Will do!
>
> Of course, it turns out that lockdep also doesn't like waited-on
> smp_call_function_single() invocations from timer handlers,
> so I am currently looking at other options for dealing with that
> potential use-after-free.  I am starting to like the looks of "only set
> CLOCK_SOURCE_VERIFY_PERCPU on statically allocated clocksource structures
> and let KASAN enforce this restriction", but I have not quite given up
> on making it more general.

The simplest point is in the thread under the clocksource_mutex which
prevents anything from vanishing under your feet.

Thanks,

        tglx