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SubjectRe: UBSAN: Undefined behaviour in mm/page_alloc.c
On 2018/11/09 19:10, Vlastimil Babka wrote:>>>> +	 * reclaim >= MAX_ORDER areas which will never succeed. Callers may
>>>> + * be using allocators in order of preference for an area that is
>>>> + * too large.
>>>> + */
>>>> + if (order >= MAX_ORDER) {
>>> Also, why not to add BUG_ON(gfp_mask & __GFP_NOFAIL); here?
>> Because we do not want to blow up the kernel just because of a stupid
>> usage of the allocator. Can you think of an example where it would
>> actually make any sense?
>> I would argue that such a theoretical abuse would blow up on an
>> unchecked NULL ptr access. Isn't that enough?
> Agreed.

If someone has written a module with __GFP_NOFAIL for an architecture
where PAGE_SIZE == 2048KB, and someone else tried to use that module on
another architecture where PAGE_SIZE == 4KB. You are saying that
triggering NULL pointer dereference is a fault of that user's ignorance
about MM. You are saying that everyone knows internal of MM. Sad...

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