linux-kernel - Re: [PATCH] rtmutex: ensure we wake up the top waiter

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Date:   Thu, 2 Feb 2023 08:20:40 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "open list:LOCKING PRIMITIVES" <linux-kernel@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] rtmutex: ensure we wake up the top waiter

On Thu, Feb 2, 2023 at 5:07 AM Thomas Gleixner <tglx@...utronix.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.