linux-kernel - Re: Problem with WARN_ON in mutex

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Message-ID: <20191210203225.2kvykwn35gnethjn@linutronix.de>
Date:   Tue, 10 Dec 2019 21:32:25 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        David Howells <dhowells@...hat.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: Problem with WARN_ON in mutex_trylock() and rxrpc

On 2019-12-10 20:25:38 [+0100], Peter Zijlstra wrote:
> AFAICT the only assumption it relies on are:
> 
>  - that the softirq will cleanly preempt a task. That is, the task
>    context must not change under the softirq execution.
> 
>  - that the softirq runs non-preemptible.
> 
> Now, both these properties are rather fundamental to how our softirqs
> work. And can, therefore, be relied upon, irrespective of the mutex
> implementation.

softirq is preemptible on -RT (I think you know that already but just in
case).

Sebastian