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SubjectRe: [PATCH 1/1] mm: kfence: skip kmemleak alloc in kfence_pool
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On Thu, 2022-06-23 at 13:59 +0200, Marco Elver wrote:
> On Thu, 23 Jun 2022 at 13:20, yee.lee via kasan-dev
> <kasan-dev@googlegroups.com> wrote:
> >
> > From: Yee Lee <yee.lee@mediatek.com>
> >
> > Use MEMBLOCK_ALLOC_NOLEAKTRACE to skip kmemleak registration when
> > the kfence pool is allocated from memblock. And the kmemleak_free
> > later can be removed too.
>
> Is this purely meant to be a cleanup and non-functional change?
>
> > Signed-off-by: Yee Lee <yee.lee@mediatek.com>
> >
> > ---
> > mm/kfence/core.c | 18 ++++++++----------
> > 1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> > index 4e7cd4c8e687..0d33d83f5244 100644
> > --- a/mm/kfence/core.c
> > +++ b/mm/kfence/core.c
> > @@ -600,14 +600,6 @@ static unsigned long kfence_init_pool(void)
> > addr += 2 * PAGE_SIZE;
> > }
> >
> > - /*
> > - * The pool is live and will never be deallocated from this
> > point on.
> > - * Remove the pool object from the kmemleak object tree, as
> > it would
> > - * otherwise overlap with allocations returned by
> > kfence_alloc(), which
> > - * are registered with kmemleak through the slab post-alloc
> > hook.
> > - */
> > - kmemleak_free(__kfence_pool);
>
> This appears to only be a non-functional change if the pool is
> allocated early. If the pool is allocated late using page-alloc, then
> there'll not be a kmemleak_free() on that memory and we'll have the
> same problem.

Do you mean the kzalloc(slab_is_available) in memblock_allc()? That
implies that MEMBLOCK_ALLOC_NOLEAKTRACE has no guarantee skipping
kmemleak_alloc from this. (Maybe add it?)

If so, we cannot identify later the block is stored in the phys
tree(memblock) or the virt tree(page_alloc).


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