netdev - Re: [PATCH net-next v1 1/1] net: usb: lan78xx: fix WARN in __netif_napi_del

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Message-ID: <20250623165537.53558fdb@kernel.org>
Date: Mon, 23 Jun 2025 16:55:37 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Oleksij Rempel <o.rempel@...gutronix.de>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Woojung Huh
 <woojung.huh@...rochip.com>, Andrew Lunn <andrew+netdev@...n.ch>, Russell
 King <rmk+kernel@...linux.org.uk>, Thangaraj Samynathan
 <Thangaraj.S@...rochip.com>, Rengarajan Sundararajan
 <Rengarajan.S@...rochip.com>, kernel@...gutronix.de,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 UNGLinuxDriver@...rochip.com, Phil Elwell <phil@...pberrypi.org>, Maxime
 Chevallier <maxime.chevallier@...tlin.com>, Simon Horman <horms@...nel.org>
Subject: Re: [PATCH net-next v1 1/1] net: usb: lan78xx: fix WARN in
 __netif_napi_del_locked on disconnect

On Fri, 20 Jun 2025 10:51:44 +0200 Oleksij Rempel wrote:
> A WARN may be triggered in __netif_napi_del_locked() during USB device
> disconnect:
> 
>   WARNING: CPU: 0 PID: 11 at net/core/dev.c:7417 __netif_napi_del_locked+0x2b4/0x350
> 
> This occurs because NAPI remains enabled when the device is unplugged and
> teardown begins. While `napi_disable()` was previously called in the
> `lan78xx_stop()` path, that function is not invoked on disconnect. Instead,
> when using PHYLINK, the `mac_link_down()` callback is guaranteed to run
> during disconnect, making it the correct place to disable NAPI.
> 
> Similarly, move `napi_enable()` to `mac_link_up()` to pair the lifecycle
> with actual MAC state.

Stopping and starting NAPI on link events is pretty unusual.
The problem is the disconnect handling, unregistering netdev
removes the NAPIs automatically, I think all you need is to
remove the explicit netif_napi_del() in lan78xx_disconnect().
Core will call _stop (which disables the NAPI), and then
it will del the NAPI.

> This patch is intended for `net-next` since the issue existed before the
> PHYLINK migration, but is more naturally and cleanly addressed now that
> PHYLINK manages link state transitions.

And repost that for net, please.. :)
-- 
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