Re: [PATCH] iommu/vt-d: Fix qi_batch NULL pointer with nested parent domain

[Yi Liu <yi.l.liu@intel.com>]

On 2024/12/11 16:32, Tian, Kevin wrote:
>> From: Liu, Yi L <yi.l.liu@intel.com>
>> Sent: Monday, December 9, 2024 11:07 AM
>>
>> On 2024/12/9 09:39, Baolu Lu wrote:
>>> +/* domain->qi_batch will be freed in iommu_free_domain() path. */
>>> +static int domain_qi_batch_alloc(struct dmar_domain *domain)
>>> +{
>>> +    unsigned long flags;
>>> +    int ret = 0;
>>> +
>>> +    spin_lock_irqsave(&domain->cache_lock, flags);
>>
>> I'm wondering if there is any difference using the domain->lock v.s. using
>> the domain->cache_lock. The RID attach path acquires/releases the
>> domain->lock first, and then the domain->cache_lock. While the PASID path
>> does the reverse order. Although neither of the two paths hold the locks
>> for a long duration (no A-B-B-A locking issue), it still means when a
>> domain is shared between RID and PASID path, the domain->qi_batch check
>> is
>> not in the same phase of the two paths.
>>
> 
> why is there different order between RID vs. PASID attach?

I think they should be consolidated to follow the same order to have
better readability although there is no actual problem for now.

-- 
Regards,
Yi Liu