Re: [PATCH net v2 1/1] xdp: fix xdp_return_frame() kernel BUG throw for page_pool memory model

Jesper Dangaard Brouer
2021-03-31T13:38:53Z

On Wed, 31 Mar 2021 21:25:03 +0800
Ong Boon Leong <boon.leong.ong@intel.com> wrote:

> xdp_return_frame() may be called outside of NAPI context to return
> xdpf back to page_pool. xdp_return_frame() calls __xdp_return() with
> napi_direct = false. For page_pool memory model, __xdp_return() calls
> xdp_return_frame_no_direct() unconditionally and below false negative
> kernel BUG throw happened under preempt-rt build:
>
> [ 430.450355] BUG: using smp_processor_id() in preemptible [00000000] code: modprobe/3884
> [ 430.451678] caller is __xdp_return+0x1ff/0x2e0
> [ 430.452111] CPU: 0 PID: 3884 Comm: modprobe Tainted: G U E 5.12.0-rc2+ #45
>
> Changes in v2:
> - This patch fixes the issue by making xdp_return_frame_no_direct() is
> only called if napi_direct = true, as recommended for better by
> Jesper Dangaard Brouer. Thanks!
>
> Fixes: 2539650fadbf ("xdp: Helpers for disabling napi_direct of xdp_return_frame")
> Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>

Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>

> ---
> net/core/xdp.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 05354976c1fc..858276e72c68 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -350,7 +350,8 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct,
> /* mem->id is valid, checked in xdp_rxq_info_reg_mem_model() */
> xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> page = virt_to_head_page(data);
> - napi_direct &= !xdp_return_frame_no_direct();
> + if (napi_direct && xdp_return_frame_no_direct())
> + napi_direct = false;
> page_pool_put_full_page(xa->page_pool, page, napi_direct);
> rcu_read_unlock();
> break;

--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer