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From: Will Deacon <will@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Android Kernel Team <kernel-team@android.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Peter Zijlstra <peterz@infradead.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Segher Boessenkool <segher@kernel.crashing.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: Re: [RFC PATCH 7/8] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros
Date: Mon, 13 Jan 2020 15:01:52 +0000
Message-ID: <20200113150151.GC4458@willie-the-truck> (raw)
In-Reply-To: <CAK8P3a2dBFiu37_YAvpoug-+RkKqq3i+8-Tkv5HPBag3JAEJrA@mail.gmail.com>

On Fri, Jan 10, 2020 at 08:42:37PM +0100, Arnd Bergmann wrote:
> On Fri, Jan 10, 2020 at 5:57 PM Will Deacon <will@kernel.org> wrote:
> 
> > @@ -128,10 +128,10 @@ do {                                                                      \
> >  #ifndef __smp_load_acquire
> >  #define __smp_load_acquire(p)                                          \
> >  ({                                                                     \
> > -       typeof(*p) ___p1 = READ_ONCE(*p);                               \
> > +       __unqual_scalar_typeof(*p) ___p1 = READ_ONCE(*p);               \
> >         compiletime_assert_atomic_type(*p);                             \
> >         __smp_mb();                                                     \
> > -       ___p1;                                                          \
> > +       (typeof(*p))___p1;                                              \
> >  })
> 
> Doesn't that last  (typeof(*p))___p1 mean you put the potential
> 'volatile' back on the assignment after you went through the
> effort of taking it out?

Yes, but that's ok wrt codegen since the local variable isn't volatile,
and I definitely ran into issues with 'const' if I returned the unqualified
type here.

Will

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-10 16:56 [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen Will Deacon
2020-01-10 16:56 ` [RFC PATCH 1/8] compiler/gcc: Emit build-time warning for GCC prior to version 4.8 Will Deacon
2020-01-10 17:35   ` Arnd Bergmann
2020-01-10 17:53     ` Joe Perches
2020-01-13 14:39       ` Arnd Bergmann
2020-01-13 15:35         ` Masahiro Yamada
2020-01-13 14:27     ` Will Deacon
2020-01-14 21:39     ` Nick Desaulniers
2020-01-15 10:35       ` David Laight
2020-01-15 10:49       ` Arnd Bergmann
2020-01-10 16:56 ` [RFC PATCH 2/8] netfilter: Avoid assigning 'const' pointer to non-const pointer Will Deacon
2020-01-10 16:56 ` [RFC PATCH 3/8] fault_inject: Don't rely on "return value" from WRITE_ONCE() Will Deacon
2020-01-10 16:56 ` [RFC PATCH 4/8] READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE() Will Deacon
2020-01-10 16:56 ` [RFC PATCH 5/8] READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses Will Deacon
2020-01-10 19:24   ` Arnd Bergmann
2020-01-13 16:16     ` Will Deacon
2020-01-10 16:56 ` [RFC PATCH 6/8] READ_ONCE: Drop pointer qualifiers when reading from scalar types Will Deacon
2020-01-10 18:54   ` Linus Torvalds
2020-01-13 14:59     ` Will Deacon
2020-01-13 17:42       ` Luc Van Oostenryck
2020-01-13 19:31       ` Linus Torvalds
2020-01-10 16:56 ` [RFC PATCH 7/8] locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros Will Deacon
2020-01-10 19:42   ` Arnd Bergmann
2020-01-13 15:01     ` Will Deacon [this message]
2020-01-10 16:56 ` [RFC PATCH 8/8] arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release macros Will Deacon
2020-01-10 17:45   ` Mark Rutland
2020-01-10 17:58 ` [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen Arnd Bergmann
2020-01-10 19:46 ` Arnd Bergmann
2020-01-10 20:14   ` Linus Torvalds
2020-01-13 13:03     ` Arnd Bergmann
2020-01-13 11:20 ` David Laight
2020-01-13 12:40 ` Christian Borntraeger

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