Re: [PATCH] vhost vdpa: fix the irq check for invoking irq_bypass_unregister_producer

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On Tue, 23 Feb 2021 at 10:13, Jason Wang <jasowang@xxxxxxxxxx> wrote:

On 2021/2/22 下午5:13, Gautam Dawar wrote:
> When qemu with vhost-vdpa netdevice is run for the first time, it
> works well.
> But after the VM is powered off, the next qemu run causes kernel panic
> due to
> a NULL pointer dereference in irq_bypass_register_producer().
>
> When the VM is powered off, vhost_vdpa_clean_irq() misses on calling
> irq_bypass_unregister_producer() for irq 0 because of the existing check.
>
> This leaves stale producer nodes, which are reset in
> vhost_vring_call_reset()
> when vhost_dev_init() is invoked during the second qemu run.
>
> As the node member of struct irq_bypass_producer is also initialized
> to zero, traversal on the producers list causes crash due to NULL pointer
> dereference.
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211711
> Signed-off-by: Gautam Dawar <gdawar@xxxxxxxxxx <mailto:gdawar@xxxxxxxxxx>>
>
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 62a9bb0efc55..d1c3a33c6239 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -849,7 +849,7 @@ static void vhost_vdpa_clean_irq(struct vhost_vdpa *v)
>
>         for (i = 0; i < v->nvqs; i++) {
>                 vq = &v->vqs[i];
> -               if (vq->call_ctx.producer.irq)
> +               if (vq->call_ctx.producer.irq >= 0)
> irq_bypass_unregister_producer(&vq->call_ctx.producer);


Since it's impossible to have an irq < 0 ( see
vhost_vdap_setup_vq_irq()), I think we can simply remove the check above.

Then we can call vhost_vdpa_unsetup_vq_irq() here to avoid temporary
variable like vq.


Done and submitted patch v2.
 
Thanks


>         }
>  }

Regards,
Gautam 
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