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

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

[Michael S. Tsirkin]

On Tue, Mar 15, 2022 at 05:41:30AM -0700, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.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@redhat.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

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

[Michael S. Tsirkin]

On Tue, Mar 15, 2022 at 05:41:30AM -0700, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.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")

Thanks a lot! I squashed this into the offending patch - no point in
breaking bisect. Pushed to linux. However I'm now
having second thoughts about applying that patchset - I'd like
soma analysis explaining how this got through testing.

> Signed-off-by: Tom Rix <trix@redhat.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;
> -- 
> 2.26.3

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

[Michael S. Tsirkin]

On Tue, Mar 15, 2022 at 08:03:26AM -0700, Tom Rix wrote:
> 
> On 3/15/22 6:28 AM, Michael S. Tsirkin wrote:
> > On Tue, Mar 15, 2022 at 05:41:30AM -0700, trix@redhat.com wrote:
> > > From: Tom Rix <trix@redhat.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")
> > Thanks a lot! I squashed this into the offending patch - no point in
> > breaking bisect. Pushed to linux. However I'm now
> > having second thoughts about applying that patchset - I'd like
> > soma analysis explaining how this got through testing.
> 
> static analysis is something i do treewide.
> 
> There are currently ~2500 issues in linux-next, do not panic! many are false
> positives.
> 
> It is pretty easy to setup and once you have a baseline you can filter only
> your files.
> 
> Tom

Thanks for that info! I was actually directing this question to the
contributor since the code does not look like it could have ever
worked. I don't have the hardware in question myself.


> > > Signed-off-by: Tom Rix <trix@redhat.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;
> > > -- 
> > > 2.26.3

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