Re: [RFC PATCH 1/1] x86/mm/pat: Clear VM_PAT if copy_p4d_range failed

[mawupeng <mawupeng1@huawei.com>]

On 2023/2/23 4:03, Dave Hansen wrote:
> On 2/16/23 18:56, Wupeng Ma wrote:
>> dup_mm
>>   dup_mmap
>>     copy_page_range
>>       copy_p4d_range
>>         copy_pud_range
>>           copy_pmd_range
>>             pmd_alloc
>>               __pmd_alloc
>>                 pmd_alloc_one
>>                   page = alloc_pages(gfp, 0);
>>                     if (!page)
>>                       return NULL;
>>     mmput
>>         exit_mmap
>>           unmap_vmas
>>             unmap_single_vma
>>               untrack_pfn
>>                 follow_phys
>>                   WARN_ON_ONCE(1);
> 
> What's the point of that warning in the first place?  I can certainly
> imagine follow_phys() failing for sparse mappings, for instance.  Is
> there some requirement that VM_PFNMAP can't be sparse?

Hi Dave

Thanks for reviewing.

Sorry，I have no idea why warning in the first place.

I think we can delete this WARN_ON_ONCE with another patch?