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Date: Thu, 6 Jun 2019 14:14:38 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc: Alan Stern <stern@...land.harvard.edu>,
Boqun Feng <boqun.feng@...il.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Frederic Weisbecker <fweisbec@...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>,
Andrea Parri <andrea.parri@...rulasolutions.com>,
Luc Maranget <luc.maranget@...ia.fr>,
Jade Alglave <j.alglave@....ac.uk>
Subject: Re: rcu_read_lock lost its compiler barrier
On Wed, Jun 05, 2019 at 11:05:11PM -0700, Paul E. McKenney wrote:
>
> In case you were wondering, the reason that I was giving you such
> a hard time was that from what I could see, you were pushing for no
> {READ,WRITE}_ONCE() at all. ;-)
Hmm, that's exactly what it should be in net/ipv4/inet_fragment.c.
We don't need the READ_ONCE/WRITE_ONCE (or volatile marking) at
all. Even if the compiler dices and slices the reads/writes of
"a" into a thousand pieces, it should still work if the RCU
primitives are worth their salt.
But I do concede that in the general RCU case you must have the
READ_ONCE/WRITE_ONCE calls for rcu_dereference/rcu_assign_pointer.
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
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