[Resend, still struggling with new laptop email settings] > On 28 Apr 2022, at 13:03, Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Thu, Apr 28, 2022 at 11:55:31AM +0200, Christophe Marie Francois Dupont de Dinechin wrote: >> >> >>> On 28 Apr 2022, at 11:51, Christophe Marie Francois Dupont de Dinechin <cdupontd@xxxxxxxxxx> wrote: >>> >>> >>> >>>> On 28 Apr 2022, at 11:46, Christophe Marie Francois Dupont de Dinechin <cdupontd@xxxxxxxxxx> wrote: >>>> >>>> >>>> >>>>> On 15 Apr 2022, at 05:51, Murilo Opsfelder Araújo <muriloo@xxxxxxxxxxxxx> 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 <muriloo@xxxxxxxxxxxxx> >>>>>> --- >>>>>> 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/20220414150855.2407137-4-dinechin@xxxxxxxxxx/ >>>>> >>>>> 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. >>> >>> … which also renders my own patch invalid :-/ >>> >>> Compiler warnings are good. Clearly not sufficient. >> >> Ah, I just noticed that free_cpumask_var is a noop in that case. >> >> So yes, your fix is better :-) > > ACK then? Yes. Acked-by: Christophe de Dinechin <dinechin@xxxxxxxxxx> > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
