[PATCH] atomic{64}_t: Explicitly specify data storage length and alignment

[linux@armlinux.org.uk (Russell King - ARM Linux)]

On Mon, Jul 09, 2018@03:47:41PM +0300, Alexey Brodkin wrote:
> Atomic instructions require data they operate on to be aligned
> according to data size. I.e. 32-bit atomic values must be 32-bit
> aligned while 64-bit values must be 64-bit aligned.
> 
> Otherwise even if CPU may handle not-aligend normal data access,
> still atomic instructions fail and typically raise an exception
> leaving us dead in the water.
> 
> This came-up during lengthly discussion here:
> http://lists.infradead.org/pipermail/linux-snps-arc/2018-July/004022.html
> 
> Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com>
> Cc: Will Deacon <will.deacon at arm.com>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Boqun Feng <boqun.feng at gmail.com>
> Cc: Russell King <linux at armlinux.org.uk>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Ingo Molnar <mingo at redhat.com>
> Cc: Darren Hart <dvhart at infradead.org>
> Cc: Shuah Khan <shuah at kernel.org>
> Cc: "Paul E. McKenney" <paulmck at linux.vnet.ibm.com>
> Cc: Josh Triplett <josh at joshtriplett.org>
> Cc: Steven Rostedt <rostedt at goodmis.org>
> Cc: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> Cc: Lai Jiangshan <jiangshanlai at gmail.com>
> Cc: David Laight <David.Laight at ACULAB.COM>
> Cc: Geert Uytterhoeven <geert at linux-m68k.org>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> ---
>  arch/arm/include/asm/atomic.h                                 | 2 +-
>  include/asm-generic/atomic64.h                                | 2 +-
>  include/linux/types.h                                         | 4 ++--
>  tools/include/linux/types.h                                   | 2 +-
>  tools/testing/selftests/futex/include/atomic.h                | 2 +-
>  .../rcutorture/formal/srcu-cbmc/include/linux/types.h         | 4 ++--
>  6 files changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/include/asm/atomic.h b/arch/arm/include/asm/atomic.h
> index 66d0e215a773..2ed6d7cf1407 100644
> --- a/arch/arm/include/asm/atomic.h
> +++ b/arch/arm/include/asm/atomic.h
> @@ -267,7 +267,7 @@ ATOMIC_OPS(xor, ^=, eor)
>  
>  #ifndef CONFIG_GENERIC_ATOMIC64
>  typedef struct {
> -	long long counter;
> +	u64 __aligned(8) counter;
>  } atomic64_t;

ARM doesn't need or require this change, and you're changing the type
from signed to unsigned, which is likely to break stuff.  So, NAK on
this from the ARM point of view.

-- 
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