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.
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