netdev - Re: rcu_read_lock lost its compiler barrier

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Message-ID: <20190603040114.st646bujtgyu7adn@gondor.apana.org.au>
Date:   Mon, 3 Jun 2019 12:01:14 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        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 Sun, Jun 02, 2019 at 08:47:07PM -0700, Paul E. McKenney wrote:
>
> 	CPU2:         if (b != 1)
> 	CPU2:                 b = 1;

Stop right there.  The kernel is full of code that assumes that
assignment to an int/long is atomic.  If your compiler breaks this
assumption that we can kiss the kernel good-bye.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt