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Date:   Thu, 5 Oct 2017 18:46:09 -0400
From:   Steven Rostedt <>
To:     Mathieu Desnoyers <>
Cc:     Andrea Parri <>,
        Peter Zijlstra <>,
        "Paul E. McKenney" <>,
        linux-kernel <>,
        Ingo Molnar <>,
        Lai Jiangshan <>,
        dipankar <>,
        Andrew Morton <>,
        Josh Triplett <>,
        Thomas Gleixner <>,
        David Howells <>,
        Eric Dumazet <>,
        fweisbec <>, Oleg Nesterov <>,
        Boqun Feng <>,
        Andrew Hunter <>,
        maged michael <>,
        gromer <>, Avi Kivity <>,
        Benjamin Herrenschmidt <>,
        Paul Mackerras <>,
        Michael Ellerman <>,
        Dave Watson <>,
        Alan Stern <>,
        Will Deacon <>,
        Andy Lutomirski <>,
        Ingo Molnar <>,
        Alexander Viro <>,
        Nicholas Piggin <>,
        linuxppc-dev <>,
        linux-arch <>
Subject: Re: [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited
 private command

On Thu, 5 Oct 2017 22:19:15 +0000 (UTC)
Mathieu Desnoyers <> wrote:

> AFAIU the scheduler rq->lock is held while preemption is disabled.
> synchronize_sched() is used here to ensure that all pre-existing
> preempt-off critical sections have completed.
> So saying that we use synchronize_sched() to synchronize with rq->lock
> would be stretching the truth a bit. It's actually only true because the
> scheduler holding the rq->lock is surrounded by a preempt-off
> critical section.

Not only is preemption disabled (which is true for all spinlocks, at
least with non PREEMPT_RT), but the rq->lock must also only be taken
with interrupts disabled (for PREEMPT_RT as well). Because it can also
be taken in interrupt context.

-- Steve

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