linux-kernel - Re: [PATCH v5 03/29] iommu: Apply the new iommufd_object_alloc

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Message-ID: <aDDp74yHGkhxHHJb@Asurada-Nvidia>
Date: Fri, 23 May 2025 14:34:39 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
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Subject: Re: [PATCH v5 03/29] iommu: Apply the new iommufd_object_alloc_ucmd
 helper

On Fri, May 23, 2025 at 07:49:40AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@...dia.com>
> > Sent: Sunday, May 18, 2025 11:21 AM
> > 
> > Now the new ucmd-based object allocator eases the finalize/abort routine,
> > apply this to all existing allocators that aren't protected by any lock.
> > 
> > Upgrade the for-driver vIOMMU alloctor too, and pass down to all existing
> > viommu_alloc op accordingly.
> > 
> > Note that __iommufd_object_alloc_ucmd() builds in some static tests that
> > cover both static_asserts in the iommufd_viommu_alloc(). Thus drop them.
> 
> I may overlook something, but at a quick glance the following check
> Is not covered?
> 
> -		static_assert(__same_type(struct iommufd_viommu,               \
> -					  ((drv_struct *)NULL)->member));      \

The container_of() inside __iommufd_object_alloc_ucmd() covers that:

#define container_of(ptr, type, member) ({				\
	void *__mptr = (void *)(ptr);					\
	static_assert(__same_type(*(ptr), ((type *)0)->member) ||	\ <<== here
		      __same_type(*(ptr), void),			\
		      "pointer type mismatch in container_of()");	\
	((type *)(__mptr - offsetof(type, member))); })

> Btw this patch doesn't convert all object allocations to the new helper,
> e.g. ioas. What is the criteria for when to use the old helpers vs. the
> new helpers?

Criteria is "that aren't protected by any lock" mentioned in the
line 2. The ioas has an ioas_creation_lock around finalize() :(

Thanks
Nic