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SubjectRe: [PATCH] kasan, slub: fix handling of kasan_slab_free hook
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On 03/06/2018 08:42 PM, Andrey Konovalov wrote:

>>> - if (s->flags & SLAB_KASAN && !(s->flags & SLAB_TYPESAFE_BY_RCU))
>>> - return;
>>> - do_slab_free(s, page, head, tail, cnt, addr);
>>> + slab_free_freelist_hook(s, &head, &tail);
>>> + if (head != NULL)
>>
>> That's an additional branch in non-debug fast-path. Find a way to avoid this.
>
> Hm, there supposed to be a branch here. We either have objects that we
> need to free, or we don't, and we need to do different things in those
> cases. Previously this was done with a hardcoded "if (s->flags &
> SLAB_KASAN && ..." statement, not it's a different "if (head !=
> NULL)".
>

They are different. "if (s->flags & SLAB_KASAN && ..." can be optimized away by compiler when CONFIG_KASAN=n,
"if (head != NULL)" - can not.

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