From: Arnd Bergmann <arnd@arndb.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Will Deacon <will@kernel.org>,
"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>,
Segher Boessenkool <segher@kernel.crashing.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: Re: [RFC PATCH 0/8] Rework READ_ONCE() to improve codegen
Date: Mon, 13 Jan 2020 14:03:41 +0100 [thread overview]
Message-ID: <CAK8P3a1Qvz+HB-ROy2cmtPtE2m113iBhWbdibpdQ4ycNp9u=ng@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wggv_LmrL85Ez0TLcAku8iz05VZmJxDGo=2aP2VvQtrsA@mail.gmail.com>
On Fri, Jan 10, 2020 at 9:15 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Fri, Jan 10, 2020 at 11:47 AM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > Isn't the read_barrier_depends() the only reason for actually needing
> > the temporary local variable that must not be volatile?
> >
> > If you make alpha provide its own READ_ONCE() as the first
> > step, it would seem that the rest of the series gets much easier
> > as the others can go back to the simple statement from your
>
> Hmm.. The union still would cause that "take the address of a volatile
> thing on the stack" problem, wouldn't it? And that was what caused
> most of the issues.
Ah, I was missing that there is still the union in smp_load_acquire(),
I only saw that the one in READ_ONCE() is needed only on alpha.
The number of files using smp_load_acquire() is fairly small though,
so we could consider changing it to pass both source and destination
as macro arguments and use typeof(dest) instad of typeof(source)
to avoid the volatile pointer access.
> I think the _real_ issue is how KASAN forces that odd pair of inline
> functions in order to have the annotations on the accesses.
But the inline functions (I assume you mean __write_once_size
and __read_once_size_nocheck?) are completely removed after
Will's series, so those no longer cause harm, right?
Arnd
next prev parent reply other threads:[~2020-01-13 13:04 UTC|newest]
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
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 [this message]
2020-01-13 11:20 ` David Laight
2020-01-13 12:40 ` Christian Borntraeger
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