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

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Message-ID: <f73dcdc2-a63f-44e9-9c3e-c1c6340d099f@redhat.com>
Date: Thu, 18 Dec 2025 13:14:42 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Xiaolei Wang <xiaolei.wang@...driver.com>, nicolas.ferre@...rochip.com,
 claudiu.beznea@...on.dev, andrew+netdev@...n.ch, davem@...emloft.net,
 edumazet@...gle.com, kuba@...nel.org, rmk+kernel@...linux.org.uk,
 Kexin.Hao@...driver.com
Cc: netdev@...r.kernel.org, stable@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] net: macb: Relocate mog_init_rings() callback from
 macb_mac_link_up() to macb_open()

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@...r.kernel.org
> Suggested-by: Kevin Hao <kexin.hao@...driver.com>
> Signed-off-by: Xiaolei Wang <xiaolei.wang@...driver.com>

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

/P