linux-kernel - Re: Confused about hlist_unhashed

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Message-ID: <87blqj4ddg.fsf@nanos.tec.linutronix.de>
Date:   Fri, 31 Jan 2020 20:47:23 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Eric Dumazet <edumazet@...gle.com>, Will Deacon <will@...nel.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: Confused about hlist_unhashed_lockless()

Eric Dumazet <edumazet@...gle.com> writes:
> On Fri, Jan 31, 2020 at 9:21 AM Will Deacon <will@...nel.org> wrote:
>> Without serialisation, timer_pending() as currently implemented does
>> not reliably tell you whether the timer is in the hlist. Is that not a
>> problem?
>
> No it is not a problem.

Even if we would take the base lock then this is just a snapshot, which
can be wrong at the moment the lock is dropped. So why bother?

Thanks,

        tglx