Messages in this thread | | | Date | Wed, 10 Mar 2021 14:00:18 -0800 (PST) | From | Hugh Dickins <> | Subject | Re: [PATCH v2 1/2] mm/memcg: rename mem_cgroup_split_huge_fixup to split_page_memcg |
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On Thu, 11 Mar 2021, Singh, Balbir wrote: > On 9/3/21 7:28 pm, Michal Hocko wrote: > > On Tue 09-03-21 09:37:29, Balbir Singh wrote: > >> On 4/3/21 6:40 pm, Zhou Guanghui wrote: > > [...] > >>> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE > >>> /* > >>> - * Because page_memcg(head) is not set on compound tails, set it now. > >>> + * Because page_memcg(head) is not set on tails, set it now. > >>> */ > >>> -void mem_cgroup_split_huge_fixup(struct page *head) > >>> +void split_page_memcg(struct page *head, unsigned int nr) > >>> { > >> > >> Do we need input validation on nr? Can nr be aribtrary or can we enforce > >> > >> VM_BUG_ON(!is_power_of_2(nr)); > > > > In practice this will be power of 2 but why should we bother to sanitze > > that? > > > > Just when DEBUG_VM is enabled to ensure the contract is valid, given that > nr is now variable, we could end up with subtle bugs unless we can audit > all callers. Even the power of 2 check does not catch the fact that nr > is indeed what we expect, but it still checks a large range of invalid > inputs.
I think you imagine this is something it's not.
"all callers" are __split_huge_page() and split_page() (maybe Matthew will have a third caller, maybe not). It is not something drivers will be calling directly themselves, and it won't ever get EXPORTed to them.
Hugh
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