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 <borntraeger@xxxxxxxxxx> > --- > 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.
