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SubjectRe: [PATCH] kmemleak: Do not use off-slab management with SLAB_NOLEAKTRACE
Hi Catalin,

Catalin Marinas wrote:
> With the slab allocator, if off-slab management is enabled for the
> kmem_caches used by kmemleak, it leads to recursive calls into
> kmemleak_alloc(). Off-slab management can be triggered by other config
> options increasing the slab size, e.g. DEBUG_PAGEALLOC.
>
> Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Pekka Enberg <penberg@cs.helsinki.fi>
> Cc: Christoph Lameter <cl@linux-foundation.org>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Forcing slabs to use on-slab management is pretty bad from memory
consumption point of view. Wouldn't it be better to annotate the
recursive calls somehow?

Pekka

> ---
> mm/slab.c | 6 ++++--
> 1 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index 7dfa481..646db30 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2261,9 +2261,11 @@ kmem_cache_create (const char *name, size_t size, size_t align,
> /*
> * Determine if the slab management is 'on' or 'off' slab.
> * (bootstrapping cannot cope with offslab caches so don't do
> - * it too early on.)
> + * it too early on. Always use on-slab management when
> + * SLAB_NOLEAKTRACE to avoid recursive calls into kmemleak)
> */
> - if ((size >= (PAGE_SIZE >> 3)) && !slab_early_init)
> + if ((size >= (PAGE_SIZE >> 3)) && !slab_early_init &&
> + !(flags & SLAB_NOLEAKTRACE))
> /*
> * Size is large, assume best to place the slab management obj
> * off-slab (should allow better packing of objs).
>



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