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 > > <[email protected]> wrote: > > > > > > > >> On 28 Apr 2022, at 11:46, Christophe Marie Francois Dupont de Dinechin > >> <[email protected]> wrote: > >> > >> > >> > >>> 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. > > > > … 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 :-)
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