netdev - Re: [Intel-wired-lan] [PATCH v1 iwl-net] igc: unregister netdev when igc_led_setup() fails in igc

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Message-ID: <87cy7yk7ma.fsf@jax.kurt.home>
Date: Wed, 10 Sep 2025 10:57:17 +0200
From: Kurt Kanzenbach <kurt@...utronix.de>
To: Kohei Enju <enjuk@...zon.com>, vitaly.lifshits@...el.com
Cc: andrew+netdev@...n.ch, anthony.l.nguyen@...el.com, davem@...emloft.net,
 edumazet@...gle.com, enjuk@...zon.com, intel-wired-lan@...ts.osuosl.org,
 kohei.enju@...il.com, kuba@...nel.org, netdev@...r.kernel.org,
 pabeni@...hat.com, przemyslaw.kitszel@...el.com,
 aleksandr.loktionov@...el.com
Subject: Re: [Intel-wired-lan] [PATCH v1 iwl-net] igc: unregister netdev
 when igc_led_setup() fails in igc_probe()

On Wed Sep 10 2025, Kohei Enju wrote:
> + Aleksandr
>
> On Wed, 10 Sep 2025 10:28:17 +0300, Lifshits, Vitaly wrote:
>
>>On 9/8/2025 9:26 AM, Kurt Kanzenbach wrote:
>>> On Sat Sep 06 2025, Kohei Enju wrote:
>>>> Currently igc_probe() doesn't unregister netdev when igc_led_setup()
>>>> fails, causing BUG_ON() in free_netdev() and then kernel panics. [1]
>>>>
>>>> This behavior can be tested using fault-injection framework. I used the
>>>> failslab feature to test the issue. [2]
>>>>
>>>> Call unregister_netdev() when igc_led_setup() fails to avoid the kernel
>>>> panic.
>>>>
>>>> [1]
>>>>   kernel BUG at net/core/dev.c:12047!
>>>>   Oops: invalid opcode: 0000 [#1] SMP NOPTI
>>>>   CPU: 0 UID: 0 PID: 937 Comm: repro-igc-led-e Not tainted 6.17.0-rc4-enjuk-tnguy-00865-gc4940196ab02 #64 PREEMPT(voluntary)
>>>>   Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
>>>>   RIP: 0010:free_netdev+0x278/0x2b0
>>>>   [...]
>>>>   Call Trace:
>>>>    <TASK>
>>>>    igc_probe+0x370/0x910
>>>>    local_pci_probe+0x3a/0x80
>>>>    pci_device_probe+0xd1/0x200
>>>>   [...]
>>>>
>>>> [2]
>>>>   #!/bin/bash -ex
>>>>
>>>>   FAILSLAB_PATH=/sys/kernel/debug/failslab/
>>>>   DEVICE=0000:00:05.0
>>>>   START_ADDR=$(grep " igc_led_setup" /proc/kallsyms \
>>>>           | awk '{printf("0x%s", $1)}')
>>>>   END_ADDR=$(printf "0x%x" $((START_ADDR + 0x100)))
>>>>
>>>>   echo $START_ADDR > $FAILSLAB_PATH/require-start
>>>>   echo $END_ADDR > $FAILSLAB_PATH/require-end
>>>>   echo 1 > $FAILSLAB_PATH/times
>>>>   echo 100 > $FAILSLAB_PATH/probability
>>>>   echo N > $FAILSLAB_PATH/ignore-gfp-wait
>>>>
>>>>   echo $DEVICE > /sys/bus/pci/drivers/igc/bind
>>>>
>>>> Fixes: ea578703b03d ("igc: Add support for LEDs on i225/i226")
>>>> Signed-off-by: Kohei Enju <enjuk@...zon.com>
>>> 
>>> Reviewed-by: Kurt Kanzenbach <kurt@...utronix.de>
>>
>>Thank you for the patch and for identifying this issue!
>>
>>I was wondering whether we could avoid failing the probe in cases where 
>>igc_led_setup fails. It seems to me that a failure in the LED class 
>>functionality shouldn't prevent the device's core functionality from 
>>working properly.
>
> Indeed, that also makes sense.
>
> The behavior that igc_probe() succeeds even if igc_led_setup() fails
> also seems good to me, as long as notifying users that igc's led
> functionality is not available.

SGTM. The LED code is nice to have, but not mandatory at all. The device
has sane LED defaults.

>
>>
>> From what I understand, errors in this function are not due to hardware 
>>malfunctions. Therefore, I suggest we remove the error propagation.
>>
>>Alternatively, if feasible, we could consider reordering the function 
>>calls so that the LED class setup occurs before the netdev registration.
>>
>
> I don't disagree with you, but I would like to hear Kurt and Aleksandr's
> opinion. Do you have any preference or suggestions?

See above.

Thanks,
Kurt

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