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

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Date:   Mon, 6 Jul 2020 08:26:56 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Naresh Kamboju <naresh.kamboju@...aro.org>,
        linux-serial@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        Vinod Koul <vkoul@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>, jirislaby@...nel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        ldewangan@...dia.com, Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>, Qian Cai <cai@....pw>,
        lkft-triage@...ts.linaro.org
Subject: Re: [qemu] boot failed: Unable to handle kernel NULL pointer
 dereference at virtual address 0000000000000000



On 7/6/2020 8:24 AM, Arnd Bergmann wrote:
> On Mon, Jul 6, 2020 at 5:01 PM Dave Jiang <dave.jiang@...el.com> wrote:
>> On 7/6/2020 5:53 AM, Arnd Bergmann wrote:
>>> On Mon, Jul 6, 2020 at 1:03 PM Naresh Kamboju <naresh.kamboju@...aro.org> 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
>