linux-kernel - Re: [PATCH] vDPA/ifcvf: match pointer check to use

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Message-ID: <20220315092101-mutt-send-email-mst@kernel.org>
Date:   Tue, 15 Mar 2022 09:23:36 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     trix@...hat.com
Cc:     jasowang@...hat.com, nathan@...nel.org, ndesaulniers@...gle.com,
        lingshan.zhu@...el.com, sgarzare@...hat.com,
        xieyongji@...edance.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] vDPA/ifcvf: match pointer check to use

On Tue, Mar 15, 2022 at 05:41:30AM -0700, trix@...hat.com wrote:
> From: Tom Rix <trix@...hat.com>
> 
> Clang static analysis reports this issue
> ifcvf_main.c:49:4: warning: Called function
>   pointer is null (null dereference)
>   vf->vring->cb.callback(vring->cb.private);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The check
>   vring = &vf->vring[i];
>   if (vring->cb.callback)
> 
> Does not match the use.  Change dereference so they match.
> 
> Fixes: 79333575b8bd ("vDPA/ifcvf: implement shared IRQ feature")
> Signed-off-by: Tom Rix <trix@...hat.com>
> ---
>  drivers/vdpa/ifcvf/ifcvf_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/ifcvf/ifcvf_main.c b/drivers/vdpa/ifcvf/ifcvf_main.c
> index 3b48e717e89f7..4366320fb68d3 100644
> --- a/drivers/vdpa/ifcvf/ifcvf_main.c
> +++ b/drivers/vdpa/ifcvf/ifcvf_main.c
> @@ -46,7 +46,7 @@ static irqreturn_t ifcvf_vqs_reused_intr_handler(int irq, void *arg)
>  	for (i = 0; i < vf->nr_vring; i++) {
>  		vring = &vf->vring[i];
>  		if (vring->cb.callback)
> -			vf->vring->cb.callback(vring->cb.private);
> +			vring->cb.callback(vring->cb.private);
>  	}
>  
>  	return IRQ_HANDLED;


Oh, absolutely. In fact vf->vring->cb.callback is just
vf->vring[0].cb.callback so it's wrong for any ring except 0. Does not
make sense.

So how did it work in testing then? No idea.
Zhu Lingshan, care to comment?


> -- 
> 2.26.3