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From: Dave Jiang <dave.jiang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
To: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
Cc: Naresh Kamboju
	<naresh.kamboju-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
	linux-serial-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	open list <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Vinod Koul <vkoul-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Jiri Slaby <jslaby-IBi9RG/b67k@public.gmane.org>,
	linux-arm-msm
	<linux-arm-msm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	linux-tegra <linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	jirislaby-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org,
	Greg Kroah-Hartman
	<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
	Andy Gross <agross-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Bjorn Andersson
	<bjorn.andersson-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
	ldewangan-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org,
	Thierry Reding
	<thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
	Qian Cai <cai-J5quhbR+WMc@public.gmane.org>,
	lkft-triage-cunTk1MwBs8s++Sfvej+rw@public.gmane.org
Subject: Re: [qemu] boot failed: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Date: Mon, 6 Jul 2020 08:26:56 -0700	[thread overview]
Message-ID: <ea69a0f8-af48-45a3-7969-c38e0f785599@intel.com> (raw)
In-Reply-To: <CAK8P3a2LmUVj-yhwxXeCpqdxqJpp0m-q9q9SKQpfh3tFgMXPQA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>



On 7/6/2020 8:24 AM, Arnd Bergmann wrote:
> On Mon, Jul 6, 2020 at 5:01 PM Dave Jiang <dave.jiang-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
>> On 7/6/2020 5:53 AM, Arnd Bergmann wrote:
>>> On Mon, Jul 6, 2020 at 1:03 PM Naresh Kamboju <naresh.kamboju-QSEj5FYQhm4dnm+yROfE0A@public.gmane.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
> 

WARNING: multiple messages have this Message-ID (diff)
From: Dave Jiang <dave.jiang@intel.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>,
	linux-serial@vger.kernel.org,
	open list <linux-kernel@vger.kernel.org>,
	Vinod Koul <vkoul@kernel.org>, Jiri Slaby <jslaby@suse.com>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	linux-tegra <linux-tegra@vger.kernel.org>,
	jirislaby@kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andy Gross <agross@kernel.org>,
	Bjorn Andersson <bjorn.andersson@linaro.org>,
	ldewangan@nvidia.com, Thierry Reding <thierry.reding@gmail.com>,
	Jon Hunter <jonathanh@nvidia.com>, Qian Cai <cai@lca.pw>,
	lkft-triage@lists.linaro.org
Subject: Re: [qemu] boot failed: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Date: Mon, 6 Jul 2020 08:26:56 -0700	[thread overview]
Message-ID: <ea69a0f8-af48-45a3-7969-c38e0f785599@intel.com> (raw)
In-Reply-To: <CAK8P3a2LmUVj-yhwxXeCpqdxqJpp0m-q9q9SKQpfh3tFgMXPQA@mail.gmail.com>



On 7/6/2020 8:24 AM, Arnd Bergmann wrote:
> On Mon, Jul 6, 2020 at 5:01 PM Dave Jiang <dave.jiang@intel.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@linaro.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
> 

  parent reply	other threads:[~2020-07-06 15:26 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-06 11:03 [qemu] boot failed: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000 Naresh Kamboju
2020-07-06 11:03 ` Naresh Kamboju
     [not found] ` <CA+G9fYvqW-RQxt3kSoNkh5Y2REoe0QQB_dTz_KPzhJzcwiM5OA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-07-06 12:53   ` Arnd Bergmann
2020-07-06 12:53     ` Arnd Bergmann
     [not found]     ` <CAK8P3a1Lda8HhsDvDREf-cOgb4RkCgEKK5Q-Zj+UhK8tsAaBLw-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-07-06 14:33       ` Dave Jiang
2020-07-06 14:33         ` Dave Jiang
2020-07-06 15:10         ` Vinod Koul
2020-07-06 15:01     ` Dave Jiang
     [not found]       ` <51d6e5bb-3de1-36dc-15a4-c341b23ca8cd-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2020-07-06 15:24         ` Arnd Bergmann
2020-07-06 15:24           ` Arnd Bergmann
     [not found]           ` <CAK8P3a2LmUVj-yhwxXeCpqdxqJpp0m-q9q9SKQpfh3tFgMXPQA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2020-07-06 15:26             ` Dave Jiang [this message]
2020-07-06 15:26               ` Dave Jiang
2020-07-06 17:36         ` Naresh Kamboju
2020-07-06 17:36           ` Naresh Kamboju

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