RE: [PATCH net v2 1/2] net: ethernet: oa_tc6: Protect skb pointer used by two different kernel instances

[Selvamani Rajagopal]

> -----Original Message-----
> From: Jakub Kicinski <kuba@xxxxxxxxxx>
> Subject: Re: [PATCH net v2 1/2] net: ethernet: oa_tc6: Protect skb pointer used by two
> different kernel instances
> 
> 
> On Fri, 26 Jun 2026 08:35:18 -0700 Selvamani Rajagopal via B4 Relay
> wrote:
> > Threaded IRQ uses waiting_tx_skb. Transmit path also uses
> > this pointer without any mutual exclusion protection. As a
> > result, it might leak skb buffer, particularly threaded IRQ
> > runs in the middle of tranmsmit path, near skb_linearize.
> 
> Can you say more ? only xmit sets waiting_tx_skb, the IRQ
> clears it. So why is IRQ racing with xmit leading to drops?

I believe xmit path and IRQ thread would run in different kernel instances. Imagine oa_tc6_try_spi_transfer
call fails in threaded IRQ. It would set disable_irq. If xmit function didn't see that when it checked, but it is set
before placing skb buffer in the waiting_tx_skb pointer (due to skb_linearize for example), the skb would be stuck
in waiting_tx_skb.

Also, See the Sashiko review that gave a SMP use-case. If you search for CPU0 0r CPU1, you would find the use case.

https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260611-level-trigger-v5-0-4533a9e85ce2%40onsemi.com