linux-kernel - Re: rcu_read_lock lost its compiler barrier

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Message-ID: <CAHk-=whLGKOmM++OQi5GX08_dfh8Xfz9Wq7khPo+MVtPYh_8hw@mail.gmail.com>
Date:   Sun, 2 Jun 2019 13:54:12 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Fengguang Wu <fengguang.wu@...el.com>, LKP <lkp@...org>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: rcu_read_lock lost its compiler barrier

On Sat, Jun 1, 2019 at 10:56 PM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> You can't then go and decide to remove the compiler barrier!  To do
> that you'd need to audit every single use of rcu_read_lock in the
> kernel to ensure that they're not depending on the compiler barrier.

What's the possible case where it would matter when there is no preemption?

          Linus