Re: [PATCH v2] net: macb: Relocate mog_init_rings() callback from macb_mac_link_up() to macb_open()

[Paolo Abeni <pabeni@redhat.com>]

On 12/9/25 9:52 AM, Xiaolei Wang wrote:
> In the non-RT kernel, local_bh_disable() merely disables preemption,
> whereas it maps to an actual spin lock in the RT kernel. Consequently,
> when attempting to refill RX buffers via netdev_alloc_skb() in
> macb_mac_link_up(), a deadlock scenario arises as follows:
>   Chain caused by macb_mac_link_up():
>    &bp->lock --> (softirq_ctrl.lock)
> 
>    Chain caused by macb_start_xmit():
>    (softirq_ctrl.lock) --> _xmit_ETHER#2 --> &bp->lock

Including the whole lockdep splat instead of the above would be clearer;
in fact, I had to fetch the relevant info from there.

> Notably, invoking the mog_init_rings() callback upon link establishment
> is unnecessary. Instead, we can exclusively call mog_init_rings() within
> the ndo_open() callback. This adjustment resolves the deadlock issue.
> Given that mog_init_rings() is only applicable to
> non-MACB_CAPS_MACB_IS_EMAC cases, we can simply move it to macb_open()
> and simultaneously eliminate the MACB_CAPS_MACB_IS_EMAC check.

This part is not clear to me: AFAICS the new code now does such init
step unconditionally, which looks confusing. I think such step should
still be under the relevant conditional (or you need to include a
better/more verbose explanation describing why such check is not really
needed).

> Fixes: 633e98a711ac ("net: macb: use resolved link config in mac_link_up()")
> Cc: stable@vger.kernel.org
> Suggested-by: Kevin Hao <kexin.hao@windriver.com>
> Signed-off-by: Xiaolei Wang <xiaolei.wang@windriver.com>

Side note: you still need to include the 'net' tag into the subj prefix.

/P