"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/
