Am 25.11.2014 um 13:38 schrieb Christian Borntraeger:
> ACCESS_ONCE does not work reliably on non-scalar types. For
> example gcc 4.6 and 4.7 might remove the volatile tag for such
> accesses during the SRA (scalar replacement of aggregates) step
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)
>
> Change the spinlock code to replace ACCESS_ONCE with READ_ONCE
> and ASSIGN_ONCE.
>
> Signed-off-by: Christian Borntraeger <[email protected]>
> ---
> arch/x86/include/asm/spinlock.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
> index 9295016..af6e673 100644
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -92,7 +92,7 @@ static __always_inline void arch_spin_lock(arch_spinlock_t
> *lock)
> unsigned count = SPIN_THRESHOLD;
>
> do {
> - if (ACCESS_ONCE(lock->tickets.head) == inc.tail)
> + if (ASSIGN_ONCE(inc.tail, lock->tickets.head))
As Mike pointed out: this should be
if (READ_ONCE(lock->tickets.head) == inc.tail)
of course.
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