[net,v2,2/2] tuntap: correctly add the missing xdp flush
diff mbox series

Message ID 1519280658-4918-2-git-send-email-jasowang@redhat.com
State New, archived
Headers show
Series
  • [net,v2,1/2] Revert "tuntap: add missing xdp flush"
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Commit Message

Jason Wang Feb. 22, 2018, 6:24 a.m. UTC
Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the
devmap stall caused by missed xdp flush by counting the pending xdp
redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or
MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was
called under process context with preemption enabled. Simply disable
preemption may silent the warning but be not enough since process may
move between different CPUS during a batch which cause xdp_do_flush()
misses some CPU where the process run previously. Consider the several
fallouts, that commit was reverted. To fix the issue correctly, we can
simply calling xdp_do_flush() immediately after xdp_do_redirect(),
a side effect is that this removes any possibility of batching which
could be addressed in the future.

Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
Fixes: 762c330d670e ("tuntap: add missing xdp flush")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/net/tun.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Sergei Shtylyov Feb. 22, 2018, 7:54 a.m. UTC | #1
Hello!

On 2/22/2018 9:24 AM, Jason Wang wrote:

> Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the
> devmap stall caused by missed xdp flush by counting the pending xdp
> redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or
> MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was

    Lead to BUG().

> called under process context with preemption enabled. Simply disable

    s/under/in the/?

> preemption may silent the warning but be not enough since process may

    Silence.

> move between different CPUS during a batch which cause xdp_do_flush()
> misses some CPU where the process run previously. Consider the several
> fallouts, that commit was reverted. To fix the issue correctly, we can
> simply calling xdp_do_flush() immediately after xdp_do_redirect(),

    Call.

> a side effect is that this removes any possibility of batching which
> could be addressed in the future.
> 
> Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
> Fixes: 762c330d670e ("tuntap: add missing xdp flush")
> Signed-off-by: Jason Wang <jasowang@redhat.com>
[...]

MBR, Sergei
Jason Wang Feb. 22, 2018, 9:35 a.m. UTC | #2
On 2018年02月22日 15:54, Sergei Shtylyov wrote:
> Hello!
>
> On 2/22/2018 9:24 AM, Jason Wang wrote:
>
>> Commit 762c330d670e ("tuntap: add missing xdp flush") tries to fix the
>> devmap stall caused by missed xdp flush by counting the pending xdp
>> redirected packets and flush when it exceeds NAPI_POLL_WEIGHT or
>> MSG_MORE is clear. This may lead BUG() since xdp_do_flush() was
>
>    Lead to BUG().
>
>> called under process context with preemption enabled. Simply disable
>
>    s/under/in the/?
>
>> preemption may silent the warning but be not enough since process may
>
>    Silence.
>
>> move between different CPUS during a batch which cause xdp_do_flush()
>> misses some CPU where the process run previously. Consider the several
>> fallouts, that commit was reverted. To fix the issue correctly, we can
>> simply calling xdp_do_flush() immediately after xdp_do_redirect(),
>
>    Call.
>
>> a side effect is that this removes any possibility of batching which
>> could be addressed in the future.
>>
>> Reported-by: Christoffer Dall <christoffer.dall@linaro.org>
>> Fixes: 762c330d670e ("tuntap: add missing xdp flush")
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
> [...]
>
> MBR, Sergei

My bad, let me post v3.

Thanks

Patch
diff mbox series

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2823a4a..a363ea2 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1662,6 +1662,7 @@  static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 			get_page(alloc_frag->page);
 			alloc_frag->offset += buflen;
 			err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);
+			xdp_do_flush_map();
 			if (err)
 				goto err_redirect;
 			rcu_read_unlock();