From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>,
David Howells <dhowells@redhat.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@kernel.org>,
linux-kernel@vger.kernel.org,
Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: Problem with WARN_ON in mutex_trylock() and rxrpc
Date: Tue, 10 Dec 2019 22:53:56 +0100 [thread overview]
Message-ID: <20191210215356.GC11457@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20191210203225.2kvykwn35gnethjn@linutronix.de>
On Tue, Dec 10, 2019 at 09:32:25PM +0100, Sebastian Andrzej Siewior wrote:
> 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).
Indeed, but there it also runs in task context and then it all works
naturally. The !preempt thing is required for when it runs on top of a
task; then it functions as a priority ceiling like construct.
prev parent reply other threads:[~2019-12-10 21:54 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-05 12:02 Problem with WARN_ON in mutex_trylock() and rxrpc David Howells
2019-12-05 13:22 ` Peter Zijlstra
2019-12-06 12:32 ` Peter Zijlstra
2019-12-10 18:33 ` Thomas Gleixner
2019-12-10 19:25 ` Peter Zijlstra
2019-12-10 20:32 ` Sebastian Andrzej Siewior
2019-12-10 21:53 ` Peter Zijlstra [this message]
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