Re: [PATCH 1/1] staging: ion: Prevent incorrect reference counting behavour

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On Thu, 25 Nov 2021, Greg KH wrote:

> On Thu, Nov 25, 2021 at 12:02:34PM +0000, Lee Jones wrote:
> > Supply additional checks in order to prevent unexpected results.
> > 
> > Fixes: b892bf75b2034 ("ion: Switch ion to use dma-buf")
> > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > ---
> >  drivers/staging/android/ion/ion.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> > index 806e9b30b9dc8..30f359faba575 100644
> > --- a/drivers/staging/android/ion/ion.c
> > +++ b/drivers/staging/android/ion/ion.c
> > @@ -509,6 +509,9 @@ static void *ion_handle_kmap_get(struct ion_handle *handle)
> >  	void *vaddr;
> >  
> >  	if (handle->kmap_cnt) {
> > +		if (handle->kmap_cnt + 1 < handle->kmap_cnt)
> 
> What about using the nice helpers in overflow.h for this?

I haven't heard of these before.

Looks like they're not widely used.

I'll try them out and see how they go.

> > +			return ERR_PTR(-EOVERFLOW);
> > +
> >  		handle->kmap_cnt++;
> >  		return buffer->vaddr;
> >  	}
> 
> What stable kernel branch(es) is this for?

I assumed your magic scripts could determine this from the Fixes:
tag.  I'll be more explicit in v2.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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