From: Arnd Bergmann <arnd@arndb.de>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Sami Tolvanen <samitolvanen@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Kees Cook <keescook@chromium.org>, Marco Elver <elver@google.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Matt Turner <mattst88@gmail.com>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Richard Henderson <rth@twiddle.net>,
Peter Zijlstra <peterz@infradead.org>,
Alan Stern <stern@rowland.harvard.edu>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
alpha <linux-alpha@vger.kernel.org>,
virtualization@lists.linux-foundation.org,
Android Kernel Team <kernel-team@android.com>
Subject: Re: [PATCH 04/18] alpha: Override READ_ONCE() with barriered implementation
Date: Thu, 2 Jul 2020 13:39:10 +0200 [thread overview]
Message-ID: <CAK8P3a3VrEkDf8t1CCsY+g7rtXkqBsiPOr97b1yRbz8NpjdfFA@mail.gmail.com> (raw)
In-Reply-To: <20200702111832.GC16418@willie-the-truck>
On Thu, Jul 2, 2020 at 1:18 PM Will Deacon <will@kernel.org> wrote:
> On Thu, Jul 02, 2020 at 12:08:41PM +0200, Arnd Bergmann wrote:
> > On Thu, Jul 2, 2020 at 11:48 AM Will Deacon <will@kernel.org> wrote:
> > > On Thu, Jul 02, 2020 at 10:32:39AM +0100, Mark Rutland wrote:
> Not sure I follow you here, but I can confirm that what you're worried
> about doesn't happen for the usual case of a pointer-to-volatile scalar.
>
> For example, ignoring dependency ordering:
>
> unsigned long foo(volatile unsigned long *p)
> {
> return smp_load_acquire(p) + 1;
> }
>
> Ends up looking like:
>
> unsigned long ___p1 = *(const volatile unsigned long *)p;
> smp_mb();
> (volatile unsigned long)___p1;
>
> My understanding is that casting a non-pointer type to volatile doesn't
> do anything, so we're good.
Right, I mixed up the correct
(typeof(*p))___p;
with the incorrect
*typeof(p)&___p;
which would dereference a volatile pointer and cause the
problem.
The code is all fine then.
Arnd
WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@arndb.de>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Sami Tolvanen <samitolvanen@google.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Kees Cook <keescook@chromium.org>, Marco Elver <elver@google.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Matt Turner <mattst88@gmail.com>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Richard Henderson <rth@twiddle.net>,
Peter Zijlstra <peterz@infradead.org>,
Alan Stern <stern@rowland.harvard.edu>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
alpha <linux-alpha@vger.k>
Subject: Re: [PATCH 04/18] alpha: Override READ_ONCE() with barriered implementation
Date: Thu, 2 Jul 2020 13:39:10 +0200 [thread overview]
Message-ID: <CAK8P3a3VrEkDf8t1CCsY+g7rtXkqBsiPOr97b1yRbz8NpjdfFA@mail.gmail.com> (raw)
In-Reply-To: <20200702111832.GC16418@willie-the-truck>
On Thu, Jul 2, 2020 at 1:18 PM Will Deacon <will@kernel.org> wrote:
> On Thu, Jul 02, 2020 at 12:08:41PM +0200, Arnd Bergmann wrote:
> > On Thu, Jul 2, 2020 at 11:48 AM Will Deacon <will@kernel.org> wrote:
> > > On Thu, Jul 02, 2020 at 10:32:39AM +0100, Mark Rutland wrote:
> Not sure I follow you here, but I can confirm that what you're worried
> about doesn't happen for the usual case of a pointer-to-volatile scalar.
>
> For example, ignoring dependency ordering:
>
> unsigned long foo(volatile unsigned long *p)
> {
> return smp_load_acquire(p) + 1;
> }
>
> Ends up looking like:
>
> unsigned long ___p1 = *(const volatile unsigned long *)p;
> smp_mb();
> (volatile unsigned long)___p1;
>
> My understanding is that casting a non-pointer type to volatile doesn't
> do anything, so we're good.
Right, I mixed up the correct
(typeof(*p))___p;
with the incorrect
*typeof(p)&___p;
which would dereference a volatile pointer and cause the
problem.
The code is all fine then.
Arnd
WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd@arndb.de>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
Marco Elver <elver@google.com>, Kees Cook <keescook@chromium.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Jason Wang <jasowang@redhat.com>,
Nick Desaulniers <ndesaulniers@google.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Sami Tolvanen <samitolvanen@google.com>,
alpha <linux-alpha@vger.kernel.org>,
Alan Stern <stern@rowland.harvard.edu>,
Matt Turner <mattst88@gmail.com>,
virtualization@lists.linux-foundation.org,
Android Kernel Team <kernel-team@android.com>,
Boqun Feng <boqun.feng@gmail.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH 04/18] alpha: Override READ_ONCE() with barriered implementation
Date: Thu, 2 Jul 2020 13:39:10 +0200 [thread overview]
Message-ID: <CAK8P3a3VrEkDf8t1CCsY+g7rtXkqBsiPOr97b1yRbz8NpjdfFA@mail.gmail.com> (raw)
In-Reply-To: <20200702111832.GC16418@willie-the-truck>
On Thu, Jul 2, 2020 at 1:18 PM Will Deacon <will@kernel.org> wrote:
> On Thu, Jul 02, 2020 at 12:08:41PM +0200, Arnd Bergmann wrote:
> > On Thu, Jul 2, 2020 at 11:48 AM Will Deacon <will@kernel.org> wrote:
> > > On Thu, Jul 02, 2020 at 10:32:39AM +0100, Mark Rutland wrote:
> Not sure I follow you here, but I can confirm that what you're worried
> about doesn't happen for the usual case of a pointer-to-volatile scalar.
>
> For example, ignoring dependency ordering:
>
> unsigned long foo(volatile unsigned long *p)
> {
> return smp_load_acquire(p) + 1;
> }
>
> Ends up looking like:
>
> unsigned long ___p1 = *(const volatile unsigned long *)p;
> smp_mb();
> (volatile unsigned long)___p1;
>
> My understanding is that casting a non-pointer type to volatile doesn't
> do anything, so we're good.
Right, I mixed up the correct
(typeof(*p))___p;
with the incorrect
*typeof(p)&___p;
which would dereference a volatile pointer and cause the
problem.
The code is all fine then.
Arnd
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-07-02 11:39 UTC|newest]
Thread overview: 200+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-30 17:37 [PATCH 00/18] Allow architectures to override __READ_ONCE() Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 01/18] tools: bpf: Use local copy of headers including uapi/linux/filter.h Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-07-01 16:38 ` Alexei Starovoitov
2020-07-01 16:38 ` Alexei Starovoitov
2020-07-01 16:38 ` Alexei Starovoitov
2020-07-01 16:38 ` Alexei Starovoitov
2020-06-30 17:37 ` [PATCH 02/18] compiler.h: Split {READ,WRITE}_ONCE definitions out into rwonce.h Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 02/18] compiler.h: Split {READ, WRITE}_ONCE " Will Deacon
2020-06-30 17:37 ` [PATCH 02/18] compiler.h: Split {READ,WRITE}_ONCE " Will Deacon
2020-06-30 19:11 ` Arnd Bergmann
2020-06-30 19:11 ` [PATCH 02/18] compiler.h: Split {READ, WRITE}_ONCE " Arnd Bergmann
2020-06-30 19:11 ` [PATCH 02/18] compiler.h: Split {READ,WRITE}_ONCE " Arnd Bergmann
2020-07-01 10:16 ` Will Deacon
2020-07-01 10:16 ` Will Deacon
2020-07-01 10:16 ` Will Deacon
2020-07-01 11:33 ` Arnd Bergmann
2020-07-01 11:33 ` [PATCH 02/18] compiler.h: Split {READ, WRITE}_ONCE " Arnd Bergmann
2020-07-01 11:33 ` [PATCH 02/18] compiler.h: Split {READ,WRITE}_ONCE " Arnd Bergmann
2020-06-30 17:37 ` [PATCH 03/18] asm/rwonce: Allow __READ_ONCE to be overridden by the architecture Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 04/18] alpha: Override READ_ONCE() with barriered implementation Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-07-02 9:32 ` Mark Rutland
2020-07-02 9:32 ` Mark Rutland
2020-07-02 9:32 ` Mark Rutland
2020-07-02 9:32 ` Mark Rutland
2020-07-02 9:48 ` Will Deacon
2020-07-02 9:48 ` Will Deacon
2020-07-02 9:48 ` Will Deacon
2020-07-02 9:48 ` Will Deacon
2020-07-02 10:08 ` Arnd Bergmann
2020-07-02 10:08 ` Arnd Bergmann
2020-07-02 10:08 ` Arnd Bergmann
2020-07-02 11:18 ` Will Deacon
2020-07-02 11:18 ` Will Deacon
2020-07-02 11:18 ` Will Deacon
2020-07-02 11:39 ` Arnd Bergmann [this message]
2020-07-02 11:39 ` Arnd Bergmann
2020-07-02 11:39 ` Arnd Bergmann
2020-07-02 14:43 ` Joel Fernandes
2020-07-02 14:43 ` Joel Fernandes
2020-07-02 14:43 ` Joel Fernandes
2020-07-02 14:55 ` Will Deacon
2020-07-02 14:55 ` Will Deacon
2020-07-02 14:55 ` Will Deacon
2020-07-02 15:07 ` Joel Fernandes
2020-07-02 15:07 ` Joel Fernandes
2020-07-02 15:07 ` Joel Fernandes
2020-06-30 17:37 ` [PATCH 05/18] asm/rwonce: Remove smp_read_barrier_depends() invocation Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 06/18] vhost: Remove redundant use of read_barrier_depends() barrier Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 07/18] alpha: Replace smp_read_barrier_depends() usage with smp_[r]mb() Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 08/18] locking/barriers: Remove definitions for [smp_]read_barrier_depends() Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 09/18] Documentation/barriers: Remove references to [smp_]read_barrier_depends() Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 10/18] Documentation/barriers/kokr: " Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 11/18] tools/memory-model: Remove smp_read_barrier_depends() from informal doc Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 12/18] include/linux: Remove smp_read_barrier_depends() from comments Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 13/18] checkpatch: Remove checks relating to [smp_]read_barrier_depends() Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 14/18] arm64: Reduce the number of header files pulled into vmlinux.lds.S Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 15/18] arm64: alternatives: Split up alternative.h Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 16/18] arm64: cpufeatures: Add capability for LDAPR instruction Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 17/18] arm64: alternatives: Remove READ_ONCE() usage during patch operation Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` [PATCH 18/18] arm64: lto: Strengthen READ_ONCE() to acquire when CLANG_LTO=y Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 17:37 ` Will Deacon
2020-06-30 19:25 ` Arnd Bergmann
2020-06-30 19:25 ` Arnd Bergmann
2020-06-30 19:25 ` Arnd Bergmann
2020-07-01 10:19 ` Will Deacon
2020-07-01 10:19 ` Will Deacon
2020-07-01 10:19 ` Will Deacon
2020-07-01 10:59 ` Arnd Bergmann
2020-07-01 10:59 ` Arnd Bergmann
2020-07-01 10:59 ` Arnd Bergmann
2020-06-30 19:47 ` Marco Elver
2020-06-30 19:47 ` Marco Elver
2020-06-30 19:47 ` Marco Elver
2020-06-30 20:20 ` Peter Zijlstra
2020-06-30 20:20 ` Peter Zijlstra
2020-06-30 20:20 ` Peter Zijlstra
2020-06-30 22:57 ` Sami Tolvanen
2020-06-30 22:57 ` Sami Tolvanen
2020-06-30 22:57 ` Sami Tolvanen
2020-07-01 10:25 ` Will Deacon
2020-07-01 10:25 ` Will Deacon
2020-07-01 10:25 ` Will Deacon
2020-07-01 10:24 ` Will Deacon
2020-07-01 10:24 ` Will Deacon
2020-07-01 10:24 ` Will Deacon
2020-07-01 17:07 ` Dave P Martin
2020-07-01 17:07 ` Dave P Martin
2020-07-01 17:07 ` Dave P Martin
2020-07-02 7:23 ` Will Deacon
2020-07-02 7:23 ` Will Deacon
2020-07-02 7:23 ` Will Deacon
2020-07-06 16:00 ` Dave Martin
2020-07-06 16:00 ` Dave Martin
2020-07-06 16:00 ` Dave Martin
2020-07-06 16:34 ` Paul E. McKenney
2020-07-06 16:34 ` Paul E. McKenney
2020-07-06 16:34 ` Paul E. McKenney
2020-07-06 17:05 ` Dave Martin
2020-07-06 17:05 ` Dave Martin
2020-07-06 17:05 ` Dave Martin
2020-07-06 17:05 ` Dave Martin
2020-07-06 17:36 ` Paul E. McKenney
2020-07-06 17:36 ` Paul E. McKenney
2020-07-06 17:36 ` Paul E. McKenney
2020-07-06 17:36 ` Paul E. McKenney
2020-07-07 10:29 ` Dave Martin
2020-07-07 10:29 ` Dave Martin
2020-07-07 10:29 ` Dave Martin
2020-07-07 10:29 ` Dave Martin
2020-07-07 22:51 ` Paul E. McKenney
2020-07-07 22:51 ` Paul E. McKenney
2020-07-07 22:51 ` Paul E. McKenney
2020-07-07 22:51 ` Paul E. McKenney
2020-07-07 23:01 ` Nick Desaulniers
2020-07-07 23:01 ` Nick Desaulniers
2020-07-08 7:15 ` Marco Elver
2020-07-08 7:15 ` Marco Elver
2020-07-08 7:15 ` Marco Elver
2020-07-08 9:16 ` Peter Zijlstra
2020-07-08 9:16 ` Peter Zijlstra
2020-07-08 9:16 ` Peter Zijlstra
2020-07-08 18:20 ` Paul E. McKenney
2020-07-08 18:20 ` Paul E. McKenney
2020-07-08 18:20 ` Paul E. McKenney
2020-07-06 18:35 ` Will Deacon
2020-07-06 18:35 ` Will Deacon
2020-07-06 18:35 ` Will Deacon
2020-07-06 19:23 ` Marco Elver
2020-07-06 19:23 ` Marco Elver
2020-07-06 19:23 ` Marco Elver
2020-07-06 19:42 ` Paul E. McKenney
2020-07-06 19:42 ` Paul E. McKenney
2020-07-06 19:42 ` Paul E. McKenney
2020-07-06 19:42 ` Paul E. McKenney
2020-07-06 16:08 ` Dave Martin
2020-07-06 16:08 ` Dave Martin
2020-07-06 16:08 ` Dave Martin
2020-07-06 18:35 ` Will Deacon
2020-07-06 18:35 ` Will Deacon
2020-07-06 18:35 ` Will Deacon
2020-07-07 10:10 ` Dave Martin
2020-07-07 10:10 ` Dave Martin
2020-07-07 10:10 ` Dave Martin
2020-07-01 7:38 ` [PATCH 00/18] Allow architectures to override __READ_ONCE() Josh Triplett
2020-07-01 7:38 ` Josh Triplett
2020-07-01 7:38 ` Josh Triplett
2020-07-01 7:38 ` Josh Triplett
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAK8P3a3VrEkDf8t1CCsY+g7rtXkqBsiPOr97b1yRbz8NpjdfFA@mail.gmail.com \
--to=arnd@arndb.de \
--cc=boqun.feng@gmail.com \
--cc=catalin.marinas@arm.com \
--cc=elver@google.com \
--cc=ink@jurassic.park.msu.ru \
--cc=jasowang@redhat.com \
--cc=josh@joshtriplett.org \
--cc=keescook@chromium.org \
--cc=kernel-team@android.com \
--cc=linux-alpha@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mattst88@gmail.com \
--cc=mst@redhat.com \
--cc=ndesaulniers@google.com \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=rth@twiddle.net \
--cc=samitolvanen@google.com \
--cc=stern@rowland.harvard.edu \
--cc=virtualization@lists.linux-foundation.org \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.