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 <[email protected]>
---
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();
page_pool_put_full_page(xa->page_pool, page, napi_direct);
rcu_read_unlock();
break;
--
2.25.1
On Mon, 29 Mar 2021 16:00:39 +0800
Ong Boon Leong <[email protected]> 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 <[email protected]>
> ---
This looks correct to me.
Acked-by: Jesper Dangaard Brouer <[email protected]>
> 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?
> 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
Jesper Dangaard Brouer <[email protected]> writes:
> On Mon, 29 Mar 2021 16:00:39 +0800
> Ong Boon Leong <[email protected]> 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 <[email protected]>
>> ---
>
> This looks correct to me.
>
> Acked-by: Jesper Dangaard Brouer <[email protected]>
>
>
>> 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
>> 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?
>
Ya, I think this is more readable. Thanks.
I will send v2.