> On 15 Apr 2022, at 05:51, Murilo Opsfelder Araújo <[email protected]>
> wrote:
>
> On 4/14/22 23:30, Murilo Opsfelder Araujo wrote:
>> GCC 12 enhanced -Waddress when comparing array address to null [0],
>> which warns:
>> drivers/virtio/virtio_pci_common.c: In function ‘vp_del_vqs’:
>> drivers/virtio/virtio_pci_common.c:257:29: warning: the comparison will
>> always evaluate as ‘true’ for the pointer operand in
>> ‘vp_dev->msix_affinity_masks + (sizetype)((long unsigned int)i * 256)’ must
>> not be NULL [-Waddress]
>> 257 | if (vp_dev->msix_affinity_masks[i])
>> | ^~~~~~
>> In fact, the verification is comparing the result of a pointer
>> arithmetic, the address "msix_affinity_masks + i", which will always
>> evaluate to true.
>> Under the hood, free_cpumask_var() calls kfree(), which is safe to pass
>> NULL, not requiring non-null verification. So remove the verification
>> to make compiler happy (happy compiler, happy life).
>> [0] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102103
>> Signed-off-by: Murilo Opsfelder Araujo <[email protected]>
>> ---
>> drivers/virtio/virtio_pci_common.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>> diff --git a/drivers/virtio/virtio_pci_common.c
>> b/drivers/virtio/virtio_pci_common.c
>> index d724f676608b..5046efcffb4c 100644
>> --- a/drivers/virtio/virtio_pci_common.c
>> +++ b/drivers/virtio/virtio_pci_common.c
>> @@ -254,8 +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])
>> -
>> free_cpumask_var(vp_dev->msix_affinity_masks[i]);
>> + free_cpumask_var(vp_dev->msix_affinity_masks[i]);
>> }
>> if (vp_dev->msix_enabled) {
>
> After I sent this message, I realized that Christophe (copied here)
> had already proposed a fix:
>
> https://lore.kernel.org/lkml/[email protected]/
>
> Christophe,
>
> Since free_cpumask_var() calls kfree() and kfree() is null-safe,
> can we just drop this null verification and call free_cpumask_var() right
> away?
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.
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