Re: [qemu] boot failed: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000

[Dave Jiang]

On 7/6/2020 8:24 AM, Arnd Bergmann wrote:
> On Mon, Jul 6, 2020 at 5:01 PM Dave Jiang <dave.jiang@xxxxxxxxx> wrote:
> > On 7/6/2020 5:53 AM, Arnd Bergmann wrote:
> > > On Mon, Jul 6, 2020 at 1:03 PM Naresh Kamboju <naresh.kamboju@xxxxxxxxxx> wrote:
> >
> > Arnd,
> > I'm looking at the pl001_dma_probe(), I think we could make it more robust if it
> > uses IS_ERR_OR_NULL(chan) instead of IS_ERR(). Should I send a patch for it? I
> > suppose looking at the comment header for dma_request_chan() it does say return
> > chan ptr or error ptr. Sorry I missed that.
>
> No. IS_ERR_OR_NULL() is almost always a mistake. A function should either
> return NULL on error, or it should return an error code, but should not be
> able to return either.

Fair enough.

> Have you checked all the other 'return NULL' statements in your patch to
> ensure that they never return error pointers?

Yeah I looked over the rest of them. The ones that are returning NULL as far as 
I can tell are expected to return NULL.

>         Arnd