Am 24.11.2014 um 14:03 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 access the lock with a barrier. > > Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> > --- > arch/arm64/include/asm/spinlock.h | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/spinlock.h b/arch/arm64/include/asm/spinlock.h > index c45b7b1..f72dc64 100644 > --- a/arch/arm64/include/asm/spinlock.h > +++ b/arch/arm64/include/asm/spinlock.h > @@ -99,12 +99,15 @@ static inline int arch_spin_value_unlocked(arch_spinlock_t lock) > > static inline int arch_spin_is_locked(arch_spinlock_t *lock) > { > - return !arch_spin_value_unlocked(ACCESS_ONCE(*lock)); > + arch_spinlock_t lockval = *lock; > + barrier(); > + return !arch_spin_value_unlocked(lockval); > } > > static inline int arch_spin_is_contended(arch_spinlock_t *lock) > { > - arch_spinlock_t lockval = ACCESS_ONCE(*lock); > + arch_spinlock_t lockval = *lock; > + barrier(); > return (lockval.next - lockval.owner) > 1; > } > #define arch_spin_is_contended arch_spin_is_contended > FWIW, we could also make this with ACCESS_ONCE, but this requires to change the definition of arch_spinlock_t for arm64 to be a union. I am a bit reluctant to do these changes without being able to test. Let me know if this is preferred and if somebody else can test. Christian
