linux-kernel - Re: [RFC PATCH 13/37] mm: implement speculative handling in __handle_mm

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Date:   Sun, 2 May 2021 21:34:30 -0700
From:   Michel Lespinasse <michel@...pinasse.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Michel Lespinasse <michel@...pinasse.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>,
        Linux-Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 13/37] mm: implement speculative handling in
 __handle_mm_fault().

On Sun, May 02, 2021 at 08:40:49PM -0700, Paul E. McKenney wrote:
> @@ -634,6 +644,12 @@ do {									      \
>   * sections, invocation of the corresponding RCU callback is deferred
>   * until after the all the other CPUs exit their critical sections.
>   *
> + * In recent kernels, synchronize_rcu() and call_rcu() also wait for
> + * regions of code with preemption disabled, including regions of code
> + * with interrupts or softirqs disabled.  If your kernel is old enough
> + * for synchronize_sched() to be defined, only code enclosed within
> + * rcu_read_lock() and rcu_read_unlock() are guaranteed to be waited for.
> + *
>   * Note, however, that RCU callbacks are permitted to run concurrently
>   * with new RCU read-side critical sections.  One way that this can happen
>   * is via the following sequence of events: (1) CPU 0 enters an RCU

You still have "old enough" / "recent kernels" here. But maybe it's OK
given that you added relevant version numbers elsewhere.

Everything else looks great to me.

Thanks,

--
Michel "walken" Lespinasse