lkml.org 
[lkml]   [2021]   [Mar]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 1/2] mm/memcg: rename mem_cgroup_split_huge_fixup to split_page_memcg
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

\
 
 \ /
  Last update: 2021-03-10 23:02    [W:0.096 / U:0.380 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site