> On 22 Jun 2021, at 01:29, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
>
> On Mon, Jun 21, 2021 at 03:37:10PM +0000, Haakon Bugge wrote:
>>
>>
>>> On 21 Jun 2021, at 17:32, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
>>>
>>> On Mon, Jun 21, 2021 at 03:30:14PM +0000, Haakon Bugge wrote:
>>>>
>>>>
>>>>> On 21 Jun 2021, at 16:35, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote:
>>>>>
>>>>> On Wed, Jun 16, 2021 at 04:35:53PM +0200, Håkon Bugge wrote:
>>>>>> +#define BIT_ACCESS_FUNCTIONS(b) \
>>>>>> + static inline void set_##b(unsigned long flags) \
>>>>>> + { \
>>>>>> + /* set_bit() does not imply a memory barrier */ \
>>>>>> + smp_mb__before_atomic(); \
>>>>>> + set_bit(b, &flags); \
>>>>>> + /* set_bit() does not imply a memory barrier */ \
>>>>>> + smp_mb__after_atomic(); \
>>>>>> + }
>>>>>
>>>>> This isn't needed, set_bit/test_bit are already atomic with
>>>>> themselves, we should not need to introduce release semantics.
>>>>
>>>> They are atomic, yes. But set_bit() does not provide a memory barrier (on x86_64, yes, but not as per the Linux definition of set_bit()).
>>>>
>>>> We have (paraphrased):
>>>>
>>>> id_priv->min_rnr_timer = min_rnr_timer;
>>>> set_bit(MIN_RNR_TIMER_SET, &id_priv->flags);
>>>>
>>>> Since set_bit() does not provide a memory barrier, another thread
>>>> may observe the MIN_RNR_TIMER_SET bit in id_priv->flags, but the
>>>> id_priv->min_rnr_timer value is not yet globally visible. Hence,
>>>> IMHO, we need the memory barriers.
>>>
>>> No, you need proper locks.
>>
>> Either will work in my opinion. If you prefer locking, I can do
>> that. This is not performance critical.
>
> Yes, use locks please
With locking, there is no need for changing the bit fields to a flags variable and set/test_bit. But, for the fix to be complete, the locking must then be done all three places. Hence. I'll send one commit with locking.
Thxs, Håkon
