Re: [patch V2 02/31] genirq/msi: Add mutex for MSI list protection

[Thomas Gleixner <tglx@xxxxxxxxxxxxx>]

On Wed, Dec 08 2021 at 20:47, Jason Gunthorpe wrote:
> On Mon, Dec 06, 2021 at 11:51:05PM +0100, Thomas Gleixner wrote:
>> +++ b/kernel/irq/msi.c
>> @@ -127,12 +127,37 @@ int msi_setup_device_data(struct device
>>              return -ENOMEM;
>>  
>>      INIT_LIST_HEAD(&md->list);
>> +    mutex_init(&md->mutex);
>>      dev->msi.data = md;
>>      devres_add(dev, md);
>>      return 0;
>>  }
>>  
>>  /**
>> + * msi_lock_descs - Lock the MSI descriptor storage of a device
>> + * @dev:    Device to operate on
>> + */
>> +void msi_lock_descs(struct device *dev)
>> +{
>> +    if (WARN_ON_ONCE(!dev->msi.data))
>> +            return;
>
> Is this useful? Other places that call msi_lock_descs will continue on and 
> deref
> null dev->msi anyhow - is the dump from the WARN_ON that much better
> than the oops from the null deref here:
>
>> +    mutex_lock(&dev->msi.data->mutex);

I put it there for paranoia reasons and forgot to revist it later. In
that case yes, it's of questionable value.

Thanks,

        tglx