Re: [PATCH 3/3] virtio-pci: Use cpumask_available to fix compilation error

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Christophe de Dinechin <dinechin@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>,
	trivial@kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Zhen Lei <thunder.leizhen@huawei.com>,
	linux-kernel@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	virtualization@lists.linux-foundation.org,
	Ben Segall <bsegall@google.com>, Ingo Molnar <mingo@redhat.com>,
	Mel Gorman <mgorman@suse.de>,
	Murilo Opsfelder Araujo <muriloo@linux.ibm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: [PATCH 3/3] virtio-pci: Use cpumask_available to fix compilation error
Date: Fri, 15 Apr 2022 04:48:52 -0400	[thread overview]
Message-ID: <20220415044657-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20220414150855.2407137-4-dinechin@redhat.com>

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@dinechin.org>
> Signed-off-by: Christophe de Dinechin <dinechin@redhat.com>

There was an alternate patch proposed for this by
Murilo Opsfelder Araujo. What do you think about that approach?

> ---
>  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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