On Sun, Aug 28, 2016 at 01:56:16PM +0200, Manfred Spraul wrote: > For x86 qspinlocks, no additional memory barrier is required in > smp_mb__after_spin_lock: > > Theoretically, for qspinlock we could define two barriers: > - smp_mb__after_spin_lock: Free for x86, not free for powerpc > - smp_mb__between_spin_lock_and_spin_unlock_wait(): > Free for all archs, see queued_spin_unlock_wait for details. > > As smp_mb__between_spin_lock_and_spin_unlock_wait() is not used > in any hotpaths, the patch does not create that define yet. > > Signed-off-by: Manfred Spraul <manf...@colorfullife.com> > --- > arch/x86/include/asm/qspinlock.h | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/x86/include/asm/qspinlock.h > b/arch/x86/include/asm/qspinlock.h > index eaba080..da06433 100644 > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -61,6 +61,17 @@ static inline bool virt_spin_lock(struct qspinlock *lock) > } > #endif /* CONFIG_PARAVIRT */ > > +#ifndef smp_mb__after_spin_lock > +/** > + * smp_mb__after_spin_lock() - Provide smp_mb() after spin_lock > + * > + * queued_spin_lock() provides full memory barriers semantics, > + * thus no further memory barrier is required. See > + * queued_spin_unlock_wait() for further details. > + */ > +#define smp_mb__after_spin_lock() barrier() > +#endif
I don't get this barrier, and I from my understanding this isn't correct. Please explain more.
