linux-kernel - Re: [PATCH 3/3] virtio-pci: Use cpumask

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Message-ID: <20220415044657-mutt-send-email-mst@kernel.org>
Date:   Fri, 15 Apr 2022 04:48:52 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Christophe de Dinechin <dinechin@...hat.com>
Cc:     trivial@...nel.org, Ben Segall <bsegall@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, Mel Gorman <mgorman@...e.de>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Murilo Opsfelder Araujo <muriloo@...ux.ibm.com>
Subject: Re: [PATCH 3/3] virtio-pci: Use cpumask_available to fix compilation
 error

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@...echin.org>
> Signed-off-by: Christophe de Dinechin <dinechin@...hat.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