Re: [PATCH v4 03/10] mm/vma: rename is_vma_write_only(), separate out shared refcount put

[Vlastimil Babka]

On 1/23/26 21:12, Lorenzo Stoakes wrote:
> The is_vma_writer_only() function is misnamed - this isn't determining if
> there is only a write lock, as it checks for the presence of the
> VM_REFCNT_EXCLUDE_READERS_FLAG.
> 
> Really, it is checking to see whether readers are excluded, with a
> possibility of a false positive in the case of a detachment (there we
> expect the vma->vm_refcnt to eventually be set to
> VM_REFCNT_EXCLUDE_READERS_FLAG, whereas for an attached VMA we expect it to
> eventually be set to VM_REFCNT_EXCLUDE_READERS_FLAG + 1).
> 
> Rename the function accordingly.
> 
> Relatedly, we use a __refcount_dec_and_test() primitive directly in
> vma_refcount_put(), using the old value to determine what the reference
> count ought to be after the operation is complete (ignoring racing
> reference count adjustments).
> 
> Wrap this into a __vma_refcount_put_return() function, which we can then
> utilise in vma_mark_detached() and thus keep the refcount primitive usage
> abstracted.
> 
> This function, as the name implies, returns the value after the reference
> count has been updated.
> 
> This reduces duplication in the two invocations of this function.
> 
> Also adjust comments, removing duplicative comments covered elsewhere and
> adding more to aid understanding.
> 
> No functional change intended.
> 
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>

Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>