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From:   Wander Lairson Costa <wander@redhat.com>
Date:   Thu, 2 Feb 2023 08:20:40 -0300
Message-ID: <CAAq0SUkykcMBZqFpgM=KCZTpxWmD12eCWFZxk+AYNS8K_QBcnQ@mail.gmail.com>
Subject: Re: [PATCH] rtmutex: ensure we wake up the top waiter
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        "open list:LOCKING PRIMITIVES" <linux-kernel@vger.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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On Thu, Feb 2, 2023 at 5:07 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Tue, Jan 31 2023 at 14:53, Wander Lairson Costa wrote:
> > On Tue, Jan 31, 2023 at 02:46:19PM -0300, Wander Lairson Costa wrote:
> >> > If you have traces which show the sequence of lock events leading to
> >> > this problem, then you should be able to decode the scenario. If you
> >> > fail to extract the information, then please provide the traces so we
> >> > can stare at them.
> >> >
> >>
> >> Here we go:
> >>
> >> Let L1 and L2 be two spinlocks.
> >>
> >> Let T1 be a task holding L1 and blocked on L2. T1, currently, is the top
> >> waiter of L2.
> >>
> >> Let T2 be the task holding L2.
> >>
> >> Let T3 be a task trying to acquire L1.
> >>
> >> The following events will lead to a state in which the wait queue of L2
> >> isn't empty but nobody holds it.
>
> That explains it nicely. Care to resend with proper explanations in the
> changelog?
>

Sure thing, thanks.