> On 15 Apr 2022, at 10:48, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Thu, Apr 14, 2022 at 05:08:55PM +0200, Christophe de Dinechin wrote:
>> With GCC 12 and defconfig, we get the following error:
>>
>> | CC drivers/virtio/virtio_pci_common.o
>> | drivers/virtio/virtio_pci_common.c: In function ‘vp_del_vqs’:
>> | drivers/virtio/virtio_pci_common.c:257:29: error: the comparison will
>> | always evaluate as ‘true’ for the pointer operand in
>> | ‘vp_dev->msix_affinity_masks + (sizetype)((long unsigned int)i * 8)’
>> | must not be NULL [-Werror=address]
>> | 257 | if (vp_dev->msix_affinity_masks[i])
>> | | ^~~~~~
>>
>> This happens in the case where CONFIG_CPUMASK_OFFSTACK is not defined,
>> since we typedef cpumask_var_t as an array. The compiler is essentially
>> complaining that an array pointer cannot be NULL. This is not a very
>> important warning, but there is a function called cpumask_available that
>> seems to be defined just for that case, so the fix is easy.
>>
>> Signed-off-by: Christophe de Dinechin <christophe@xxxxxxxxxxxx>
>> Signed-off-by: Christophe de Dinechin <dinechin@xxxxxxxxxx>
>
> There was an alternate patch proposed for this by
> Murilo Opsfelder Araujo. What do you think about that approach?
I responded on the other thread, but let me share the response here:
[to muriloo@xxxxxxxxxxxxx]
Apologies for the delay in responding, broken laptop…
In the case where CONFIG_CPUMASK_OFFSTACK is not defined, we have:
typedef struct cpumask cpumask_var_t[1];
So that vp_dev->msix_affinity_masks[i] is statically not null (that’s the warning)
but also a static pointer, so not kfree-safe IMO.
>
>
>> ---
>> drivers/virtio/virtio_pci_common.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
>> index d724f676608b..5c44a2f13c93 100644
>> --- a/drivers/virtio/virtio_pci_common.c
>> +++ b/drivers/virtio/virtio_pci_common.c
>> @@ -254,7 +254,7 @@ void vp_del_vqs(struct virtio_device *vdev)
>>
>> if (vp_dev->msix_affinity_masks) {
>> for (i = 0; i < vp_dev->msix_vectors; i++)
>> - if (vp_dev->msix_affinity_masks[i])
>> + if (cpumask_available(vp_dev->msix_affinity_masks[i]))
>> free_cpumask_var(vp_dev->msix_affinity_masks[i]);
>> }
>>
>> --
>> 2.35.1
>
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