On Mon, Sep 27, 2021 at 5:24 AM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
>
> After commit ("f227f0faf63b slub: fix unreclaimable slab stat for bulk
> free"), the check for free nonslab page is replaced by VM_BUG_ON_PAGE,
> which only check with CONFIG_DEBUG_VM enabled, but this config may
> impact performance, so it only for debug.
>
> Commit ("0937502af7c9 slub: Add check for kfree() of non slab objects.")
> add the ability, which should be needed in any configs to catch the
> invalid free, they even could be potential issue, eg, memory corruption,
> use after free and double-free, so replace VM_BUG_ON_PAGE to WARN_ON, add
> dump_page() and object address printing to help use to debug the issue.
>
> Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> ---
> v2: Add object address printing suggested by Matthew Wilcox
>
> mm/slub.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 3095b889fab4..157973e22faf 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3522,7 +3522,11 @@ static inline void free_nonslab_page(struct page *page, void *object)
> {
> unsigned int order = compound_order(page);
>
> - VM_BUG_ON_PAGE(!PageCompound(page), page);
> + if (WARN_ON(!PageCompound(page))) {
If there is a problem then this would be too noisy. Why not WARN_ON_ONCE()?
> + dump_page(page, "invalid free nonslab page");
> + pr_warn("object pointer: 0x%p\n", object);
Actually why not add 'once' semantics for the whole if-block?
> + }
> +
> kfree_hook(object);
> mod_lruvec_page_state(page, NR_SLAB_UNRECLAIMABLE_B, -(PAGE_SIZE << order));
> __free_pages(page, order);
> --
> 2.26.2
>
