linux-kernel - Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs

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Date:   Sat, 29 Jun 2019 17:12:36 +0200
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Byungchul Park <byungchul.park@....com>,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Scott Wood <swood@...hat.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        rcu <rcu@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Triplett <josh@...htriplett.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>
Subject: Re: [RFC] Deadlock via recursive wakeup via RCU with threadirqs

Hi Steve,

> As Paul stated, interrupts are synchronization points. Archs can only
> play games with ordering when dealing with entities outside the CPU
> (devices and other CPUs). But if you have assembly that has two stores,
> and an interrupt comes in, the arch must guarantee that the stores are
> done in that order as the interrupt sees it.

Hopefully I'm not derailing the conversation too much with my questions
... but I was wondering if we had any documentation (or inline comments)
elaborating on this "interrupts are synchronization points"?

Thanks,
  Andrea