Re: [PATCH 2/2] xen: privcmd: Add support for ioeventfd

[Juergen Gross <jgross@suse.com>]

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On 09.10.23 12:53, Viresh Kumar wrote:
> On 09-10-23, 10:40, Alex Bennée wrote:
>> I thought generally sync points act as full barriers. Doing a bunch of
>> grepping I think ends at:
>>
>>    static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
>>    {
>>            unsigned long curr = (unsigned long)current;
>>
>>            return atomic_long_try_cmpxchg_release(&lock->owner, &curr, 0UL);
>>    }
>>
>> so you should already have completed your writes by that point.
> 
> I am not sure if depending on such indirect mechanisms to implement
> barriers for you is a good idea.
> 
> The situation here probably requires explicit barriers to make sure it
> doesn't break in future ?
> 

Depending on lock implementations to include the needed barriers is fine IMO.

That is one central objective locks must ensure: to make sure any updates in
a locked region are operating on consistent data and being observable by
others after leaving the locked region.


Juergen

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