Re: [net-next v6 0/9] Add support for per-NAPI config via netlink

[Joe Damato <jdamato@fastly.com>]

On Wed, Dec 18, 2024 at 11:22:33AM +0000, Alex Lazar wrote:
> Hi Joe and all,
> 
> I am part of the NVIDIA Eth drivers team, and we are experiencing a problem,
> sibesced to this change: commit 86e25f40aa1e ("net: napi: Add napi_config")
> 
> The issue occurs when sending packets from one machine to another.
> On the receiver side, we have XSK (XDPsock) that receives the packet and sends it
> back to the sender.
> At some point, one packet (packet A) gets "stuck," and if we send a new packet
> (packet B), it "pushes" the previous one. Packet A is then processed by the NAPI
> poll, and packet B gets stuck, and so on.
> 
> Your change involves moving napi_hash_del() and napi_hash_add() from
> netif_napi_del() and netif_napi_add_weight() to napi_enable() and napi_disable().
> If I move them back to netif_napi_del() and netif_napi_add_weight(),
> the issue is resolved (I moved the entire if/else block, not just the napi_hash_del/add).
> 
> This issue occurs with both the new and old APIs (netif_napi_add/_config).
> Moving the napi_hash_add() and napi_hash_del() functions resolves it for both.
> I am debugging this, no breakthrough so far.
> 
> I would appreciate if you could look into this.
> We can provide more details per request.

I appreciate your report, but there is not a lot in your message to
help debug the issue.

Can you please:

1.) Verify that the kernel tree you are testing on has commit
cecc1555a8c2 ("net: Make napi_hash_lock irq safe") included ? If it
does not, can you pull in that commit and re-run your test and
report back if that fixes your problem?

2.) If (1) does not fix your problem, can you please reply with at
least the following information:
  - Specify what device this is happening on (in case I have access
    to one)
  - Which driver is affected
  - Which upstream kernel SHA you are building your test kernel from
  - The reproducer program(s) with clear instructions on how exactly
    to run it/them in order to reproduce the issue

Thanks,
Joe