Re: [PATCH net v2 3/4] net: dsa: microchip: Ensure a ksz_irq is initialized before freeing it

Bastien Curutchet
2025-11-12T07:44:13Z

Hi Jakub,

On 11/11/25 3:28 AM, Jakub Kicinski wrote:
> On Thu, 06 Nov 2025 13:53:10 +0100 Bastien Curutchet (Schneider
> Electric) wrote:
>> diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
>> index 3a4516d32aa5f99109853ed400e64f8f7e2d8016..4f5e2024442692adefc69d47e82381a3c3bda184 100644
>> --- a/drivers/net/dsa/microchip/ksz_common.c
>> +++ b/drivers/net/dsa/microchip/ksz_common.c
>> @@ -2858,14 +2858,16 @@ static void ksz_irq_free(struct ksz_irq *kirq)
>> {
>> int irq, virq;
>>
>> - free_irq(kirq->irq_num, kirq);
>> + if (kirq->irq_num)
>> + free_irq(kirq->irq_num, kirq);
>>
>> for (irq = 0; irq < kirq->nirqs; irq++) {
>
> if the domain may not be registered is it okay to try to find mappings
> in it? From the init path it seems that kirq->nirqs is set to the port
> count before registration so it will not be 0 if domain is NULL.
>

I first thought it was fine because __irq_resolve_mapping() inside
irq_find_mapping() verifies that the domain isn't NULL, then
irq_find_mapping() returns 0 when it doesn't find an IRQ, and finally,
irq_dispose_mapping() returns immediately when virq is 0.

However, after taking a closer look at __irq_resolve_mapping(), I
noticed that there is a global irq_default_domain that is used by some
architectures (mainly MIPS and PowerPC) as a fallback when
__irq_resolve_mapping() is given a NULL domain. In that case, it seems
possible for the function to return a non-zero virq that has nothing to
do with us, and which would then be incorrectly released afterward by
irq_dispose_mapping().

This second case shouldn't occur often but I can move the for loop
behind the `if (kirq->domain)` check to be safe.

>> virq = irq_find_mapping(kirq->domain, irq);
>> irq_dispose_mapping(virq);
>> }
>>
>> - irq_domain_remove(kirq->domain);
>> + if (kirq->domain)
>> + irq_domain_remove(kirq->domain);

Best regards,
Bastien