From: Herbert Xu <herbert@gondor.apana.org.au>
To: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Alan Stern <stern@rowland.harvard.edu>,
Boqun Feng <boqun.feng@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Fengguang Wu <fengguang.wu@intel.com>, LKP <lkp@01.org>,
LKML <linux-kernel@vger.kernel.org>,
Netdev <netdev@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Andrea Parri <andrea.parri@amarulasolutions.com>,
Luc Maranget <luc.maranget@inria.fr>,
Jade Alglave <j.alglave@ucl.ac.uk>
Subject: Re: rcu_read_lock lost its compiler barrier
Date: Thu, 6 Jun 2019 21:38:24 +0800 [thread overview]
Message-ID: <20190606133824.aibysezb5qdo3x27@gondor.apana.org.au> (raw)
In-Reply-To: <20190606105817.GE28207@linux.ibm.com>
On Thu, Jun 06, 2019 at 03:58:17AM -0700, Paul E. McKenney wrote:
>
> I cannot immediately think of a way that the compiler could get this
> wrong even in theory, but similar code sequences can be messed up.
> The reason for this is that in theory, the compiler could use the
> stored-to location as temporary storage, like this:
>
> a = whatever; // Compiler uses "a" as a temporary
> do_something();
> whatever = a;
> a = 1; // Intended store
Well if the compiler is going to do this then surely it would
continue to do this even if you used WRITE_ONCE. Remember a is
not volatile, only the access of a through WRITE_ONCE is volatile.
Cheers,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
WARNING: multiple messages have this Message-ID (diff)
From: Herbert Xu <herbert@gondor.apana.org.au>
To: lkp@lists.01.org
Subject: Re: rcu_read_lock lost its compiler barrier
Date: Thu, 06 Jun 2019 21:38:24 +0800 [thread overview]
Message-ID: <20190606133824.aibysezb5qdo3x27@gondor.apana.org.au> (raw)
In-Reply-To: <20190606105817.GE28207@linux.ibm.com>
[-- Attachment #1: Type: text/plain, Size: 831 bytes --]
On Thu, Jun 06, 2019 at 03:58:17AM -0700, Paul E. McKenney wrote:
>
> I cannot immediately think of a way that the compiler could get this
> wrong even in theory, but similar code sequences can be messed up.
> The reason for this is that in theory, the compiler could use the
> stored-to location as temporary storage, like this:
>
> a = whatever; // Compiler uses "a" as a temporary
> do_something();
> whatever = a;
> a = 1; // Intended store
Well if the compiler is going to do this then surely it would
continue to do this even if you used WRITE_ONCE. Remember a is
not volatile, only the access of a through WRITE_ONCE is volatile.
Cheers,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
next prev parent reply other threads:[~2019-06-06 13:38 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-10 0:57 [rcu] kernel BUG at include/linux/pagemap.h:149! Fengguang Wu
2015-09-10 0:57 ` Fengguang Wu
2015-09-10 10:25 ` Boqun Feng
2015-09-10 17:16 ` Paul E. McKenney
2015-09-10 17:16 ` Paul E. McKenney
2015-09-11 2:19 ` Boqun Feng
[not found] ` <CAJzB8QG=1iZW3dQEie6ZSTLv8GZ3YSut0aL1VU7LLmiHQ1B1DQ@mail.gmail.com>
2015-09-11 21:59 ` Paul E. McKenney
2015-09-11 21:59 ` Paul E. McKenney
2015-09-12 5:46 ` Boqun Feng
2015-09-21 19:30 ` Frederic Weisbecker
2015-09-21 19:30 ` Frederic Weisbecker
2015-09-21 20:43 ` Paul E. McKenney
2015-09-21 20:43 ` Paul E. McKenney
2019-06-02 5:56 ` rcu_read_lock lost its compiler barrier Herbert Xu
2019-06-02 5:56 ` Herbert Xu
2019-06-02 20:54 ` Linus Torvalds
2019-06-02 20:54 ` Linus Torvalds
2019-06-03 2:46 ` Herbert Xu
2019-06-03 2:46 ` Herbert Xu
2019-06-03 3:47 ` Paul E. McKenney
2019-06-03 4:01 ` Herbert Xu
2019-06-03 4:01 ` Herbert Xu
2019-06-03 4:17 ` Herbert Xu
2019-06-03 4:17 ` Herbert Xu
2019-06-03 7:23 ` Paul E. McKenney
2019-06-03 8:42 ` Paul E. McKenney
2019-06-03 15:26 ` David Laight
2019-06-03 15:40 ` Linus Torvalds
2019-06-03 15:40 ` Linus Torvalds
2019-06-03 5:26 ` Herbert Xu
2019-06-03 5:26 ` Herbert Xu
2019-06-03 6:42 ` Boqun Feng
2019-06-03 6:42 ` Boqun Feng
2019-06-03 20:03 ` Paul E. McKenney
2019-06-04 14:44 ` Alan Stern
2019-06-04 14:44 ` Alan Stern
2019-06-04 16:04 ` Linus Torvalds
2019-06-04 16:04 ` Linus Torvalds
2019-06-04 17:00 ` Alan Stern
2019-06-04 17:00 ` Alan Stern
2019-06-04 17:29 ` Linus Torvalds
2019-06-04 17:29 ` Linus Torvalds
2019-06-07 14:09 ` inet: frags: Turn fqdir->dead into an int for old Alphas Herbert Xu
2019-06-07 14:09 ` Herbert Xu
2019-06-07 15:26 ` Eric Dumazet
2019-06-07 15:26 ` Eric Dumazet
2019-06-07 15:32 ` Herbert Xu
2019-06-07 15:32 ` Herbert Xu
2019-06-07 16:13 ` Eric Dumazet
2019-06-07 16:13 ` Eric Dumazet
2019-06-07 16:19 ` Linus Torvalds
2019-06-07 16:19 ` Linus Torvalds
2019-06-08 15:27 ` Paul E. McKenney
2019-06-08 17:42 ` Linus Torvalds
2019-06-08 17:42 ` Linus Torvalds
2019-06-08 17:50 ` Linus Torvalds
2019-06-08 17:50 ` Linus Torvalds
2019-06-08 18:50 ` Paul E. McKenney
2019-06-08 18:14 ` Paul E. McKenney
2019-06-06 4:51 ` rcu_read_lock lost its compiler barrier Herbert Xu
2019-06-06 4:51 ` Herbert Xu
2019-06-06 6:05 ` Paul E. McKenney
2019-06-06 6:14 ` Herbert Xu
2019-06-06 6:14 ` Herbert Xu
2019-06-06 9:06 ` Paul E. McKenney
2019-06-06 9:28 ` Herbert Xu
2019-06-06 9:28 ` Herbert Xu
2019-06-06 10:58 ` Paul E. McKenney
2019-06-06 13:38 ` Herbert Xu [this message]
2019-06-06 13:38 ` Herbert Xu
2019-06-06 13:48 ` Paul E. McKenney
2019-06-06 8:16 ` Andrea Parri
2019-06-06 14:19 ` Alan Stern
2019-06-06 14:19 ` Alan Stern
2019-06-08 15:19 ` Paul E. McKenney
2019-06-08 15:56 ` Alan Stern
2019-06-08 15:56 ` Alan Stern
2019-06-08 16:31 ` Paul E. McKenney
2019-06-03 9:35 ` Paul E. McKenney
2019-06-06 8:38 ` Andrea Parri
2019-06-06 9:32 ` Herbert Xu
2019-06-06 9:32 ` Herbert Xu
2019-06-03 0:06 ` Paul E. McKenney
2019-06-03 3:03 ` Herbert Xu
2019-06-03 3:03 ` Herbert Xu
2019-06-03 9:27 ` Paul E. McKenney
2019-06-03 15:55 ` Linus Torvalds
2019-06-03 15:55 ` Linus Torvalds
2019-06-03 16:07 ` Linus Torvalds
2019-06-03 16:07 ` Linus Torvalds
2019-06-03 19:53 ` Paul E. McKenney
2019-06-03 20:24 ` Linus Torvalds
2019-06-03 20:24 ` Linus Torvalds
2019-06-04 21:14 ` Paul E. McKenney
2019-06-05 2:21 ` Herbert Xu
2019-06-05 2:21 ` Herbert Xu
2019-06-05 3:30 ` Paul E. McKenney
2019-06-06 4:37 ` Herbert Xu
2019-06-06 4:37 ` Herbert Xu
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