"Paul E. McKenney" <paul...@linux.vnet.ibm.com> writes: > On Thu, Nov 12, 2015 at 01:31:23PM +0100, Peter Zijlstra wrote: >> Hi >> >> I think the MIPS arch_spin_unlock() is borken. >> >> spin_unlock() must have RELEASE semantics, these require that no LOADs >> nor STOREs leak out from the critical section. >> >> >From what I know MIPS has a relaxed memory model which allows reads to >> pass stores, and as implemented arch_spin_unlock() only issues a wmb >> which doesn't order prior reads vs later stores. >> >> Therefore upgrade the wmb() to smp_mb(). >> >> (Also, why the unconditional wmb, as opposed to smp_wmb() ?) > > One guess is that they want to order I/O accesses within the critical > section?
Isn't that what mmiowb() is for? >> Maybe-Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> >> --- >> diff --git a/arch/mips/include/asm/spinlock.h >> b/arch/mips/include/asm/spinlock.h >> index 40196bebe849..b2ca13f06152 100644 >> --- a/arch/mips/include/asm/spinlock.h >> +++ b/arch/mips/include/asm/spinlock.h >> @@ -140,7 +140,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock) >> static inline void arch_spin_unlock(arch_spinlock_t *lock) >> { >> unsigned int serving_now = lock->h.serving_now + 1; >> - wmb(); >> + smp_mb(); >> lock->h.serving_now = (u16)serving_now; >> nudge_writes(); >> } >> > -- Måns Rullgård m...@mansr.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/