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

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Date:   Sat, 29 Jun 2019 09:55:33 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Byungchul Park <byungchul.park@....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

On Sat, Jun 29, 2019 at 05:12:36PM +0200, Andrea Parri wrote:
> 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"?

I don't know of any, but I would suggest instead looking at something
like the Hennessey and Patterson computer-architecture textbook.

Please keep in mind that the rather detailed documentation on RCU is a
bit of an outlier due to the fact that there are not so many textbooks
that cover RCU.  If we tried to replicate all of the relevant textbooks
in the Documentation directory, it would be quite a large mess.  ;-)

							Thanx, Paul