Andrew, please ignore this one.
On Mon 30-01-17 10:49:40, Michal Hocko wrote:
> From: Michal Hocko <mhocko@xxxxxxxx>
>
> both bpf_map_area_alloc and xt_alloc_table_info try really hard to
> play nicely with large memory requests which can be triggered from
> the userspace (by an admin). See 5bad87348c70 ("netfilter: x_tables:
> avoid warn and OOM killer on vmalloc call") resp. d407bd25a204 ("bpf:
> don't trigger OOM killer under pressure with map alloc").
>
> The current allocation pattern strongly resembles kvmalloc helper except
> for one thing __GFP_NORETRY is not used for the vmalloc fallback. The
> main reason why kvmalloc doesn't really support __GFP_NORETRY is
> because vmalloc doesn't support this flag properly and it is far from
> straightforward to make it understand it because there are some hard
> coded GFP_KERNEL allocation deep in the call chains. This patch simply
> replaces the open coded variants with kvmalloc and puts a note to
> push on MM people to support __GFP_NORETRY in kvmalloc it this turns out
> to be really needed along with OOM report pointing at vmalloc.
>
> If there is an immediate need and no full support yet then
> kvmalloc(size, gfp | __GFP_NORETRY)
> will work as good as __vmalloc(gfp | __GFP_NORETRY) - in other words it
> might trigger the OOM in some cases.
>
> Cc: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: Marcelo Ricardo Leitner <marcelo.leitner@xxxxxxxxx>
> Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
> Acked-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> kernel/bpf/syscall.c | 19 +++++--------------
> net/netfilter/x_tables.c | 16 ++++++----------
> 2 files changed, 11 insertions(+), 24 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 08a4d287226b..3d38c7a51e1a 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -54,21 +54,12 @@ void bpf_register_map_type(struct bpf_map_type_list *tl)
>
> void *bpf_map_area_alloc(size_t size)
> {
> - /* We definitely need __GFP_NORETRY, so OOM killer doesn't
> - * trigger under memory pressure as we really just want to
> - * fail instead.
> + /*
> + * FIXME: we would really like to not trigger the OOM killer and rather
> + * fail instead. This is not supported right now. Please nag MM people
> + * if these OOM start bothering people.
> */
> - const gfp_t flags = __GFP_NOWARN | __GFP_NORETRY | __GFP_ZERO;
> - void *area;
> -
> - if (size <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER)) {
> - area = kmalloc(size, GFP_USER | flags);
> - if (area != NULL)
> - return area;
> - }
> -
> - return __vmalloc(size, GFP_KERNEL | __GFP_HIGHMEM | flags,
> - PAGE_KERNEL);
> + return kvzalloc(size, GFP_USER);
> }
>
> void bpf_map_area_free(void *area)
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index d529989f5791..ba8ba633da72 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -995,16 +995,12 @@ struct xt_table_info *xt_alloc_table_info(unsigned int size)
> if ((SMP_ALIGN(size) >> PAGE_SHIFT) + 2 > totalram_pages)
> return NULL;
>
> - if (sz <= (PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
> - info = kmalloc(sz, GFP_KERNEL | __GFP_NOWARN | __GFP_NORETRY);
> - if (!info) {
> - info = __vmalloc(sz, GFP_KERNEL | __GFP_NOWARN |
> - __GFP_NORETRY | __GFP_HIGHMEM,
> - PAGE_KERNEL);
> - if (!info)
> - return NULL;
> - }
> - memset(info, 0, sizeof(*info));
> + /*
> + * FIXME: we would really like to not trigger the OOM killer and rather
> + * fail instead. This is not supported right now. Please nag MM people
> + * if these OOM start bothering people.
> + */
> + info = kvzalloc(sz, GFP_KERNEL);
> info->size = size;
> return info;
> }
> --
> 2.11.0
>
--
Michal Hocko
SUSE Labs
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