Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs

[David Hildenbrand <david@redhat.com>]

On 04.06.25 21:12, Liam R. Howlett wrote:
> * David Hildenbrand <david@redhat.com> [250604 10:06]:
>> Especially once we hit one of the assertions in
>> sanity_check_pinned_pages(), observing follow-up assertions failing
>> in other code can give good clues about what went wrong, so use
>> VM_WARN_ON_ONCE instead.
>>
>> While at it, let's just convert all VM_BUG_ON to VM_WARN_ON_ONCE as
>> well. Add one comment for the pfn_valid() check.
>>
>> We have to introduce VM_WARN_ON_ONCE_VMA() to make that fly.
>>
>> Drop the BUG_ON after mmap_read_lock_killable(), if that ever returns
>> something > 0 we're in bigger trouble. Convert the other BUG_ON's into
>> VM_WARN_ON_ONCE as well, they are in a similar domain "should never
>> happen", but more reasonable to check for during early testing.
>>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
>> Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
>> Cc: Vlastimil Babka <vbabka@suse.cz>
>> Cc: Mike Rapoport <rppt@kernel.org>
>> Cc: Suren Baghdasaryan <surenb@google.com>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Jason Gunthorpe <jgg@ziepe.ca>
>> Cc: John Hubbard <jhubbard@nvidia.com>
>> Cc: Peter Xu <peterx@redhat.com>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> seems okay, besides the one nit.
> 
> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

[...]

>>   
>>   	ret = handle_mm_fault(vma, address, fault_flags, NULL);
>> @@ -1760,10 +1760,7 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
>>   		}
>>   
>>   		/* VM_FAULT_RETRY or VM_FAULT_COMPLETED cannot return errors */
>> -		if (!*locked) {
>> -			BUG_ON(ret < 0);
>> -			BUG_ON(ret >= nr_pages);
>> -		}
>> +		VM_WARN_ON_ONCE(!*locked && (ret < 0 || ret >= nr_pages));
> 
> nit, we are losing accuracy on the value of ret here.  I doubt it makes
> much of a difference though.

Yeah I doubt this will matter.

Thanks!

-- 
Cheers,

David / dhildenb