Jesper Dangaard Brouer <brouer@xxxxxxxxxx> writes:
> On Mon, 29 Mar 2021 16:00:39 +0800
> Ong Boon Leong <boon.leong.ong@xxxxxxxxx> 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
>>
>> So, this patch fixes the issue by adding "if (napi_direct)" condition
>> to skip calling xdp_return_frame_no_direct() if napi_direct = false.
>>
>> Fixes: 2539650fadbf ("xdp: Helpers for disabling napi_direct of xdp_return_frame")
>> Signed-off-by: Ong Boon Leong <boon.leong.ong@xxxxxxxxx>
>> ---
>
> This looks correct to me.
>
> Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
>
>
>> 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..4eaa28972af2 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)
>> + napi_direct &= !xdp_return_frame_no_direct();
>
> if (napi_direct && xdp_return_frame_no_direct())
> napi_direct = false;
>
> I wonder if this code would be easier to understand?
Yes, IMO it would! :)
-Toke
