linux-kernel - Re: Re: [PATCH] drivers/video/fbdev/core/fbmem.c: add pointer judgment

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Date:   Thu, 20 May 2021 09:48:29 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     宋强 <songqiang@...ontech.com>
Cc:     Matthew Wilcox <willy@...radead.org>, sam <sam@...nborg.org>,
        "b.zolnierkie" <b.zolnierkie@...sung.com>,
        penguin-kernel <penguin-kernel@...ove.sakura.ne.jp>,
        "george.kennedy" <george.kennedy@...cle.com>,
        tzimmermann <tzimmermann@...e.de>, jgg <jgg@...pe.ca>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-fbdev <linux-fbdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] drivers/video/fbdev/core/fbmem.c: add pointer judgment

>  > On Wed, May 19, 2021 at 08:00:28PM +0800, songqiang wrote:
> > Signed-off-by: songqiang <songqiang@...ontech.com>
> From: "Matthew Wilcox <willy@...radead.org>"
> > You need to explain:
> >
> > - Why you think this patch is needed
> > - Did you observe a problem at runtime?
> > - Is this the output from some checking tool?
> > - Why this is the right way to address the problem
>
On Thu, May 20, 2021 at 7:58 AM 宋强 <songqiang@...ontech.com> wrote:
>
> I find null pointer bug when I debug the kernel of loongson，I think the function fb_set_suspend()
> add pointer judgment will more friendly.

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> [  102.011018] Call Trace:
>
> [  102.013443] [<ffffffff81068e10>] fb_set_suspend+0x50/0x80
> [  102.018819] [<ffffffffc0061aa0>] loongson_drm_suspend+0x1a0/0x340 [loongson]
> [  102.025827] [<ffffffffc0061c58>] loongson_pmops_freeze+0x18/0x40 [loongson]
> [  102.032748] [<ffffffff81008fd4>] pci_pm_freeze+0x94/0x240
> [  102.038114] [<ffffffff815377e0>] dpm_run_callback.isra.5+0x20/0x140
> [  102.044341] [<ffffffff81539608>] __device_suspend+0x2c8/0x740

It looks like the check would actually belong into the loongson_drm driver.
The driver is not upstream yet, but I assume you have the source for it, so
try to fix the bug there and send the patch to the owners of that driver.

       Arnd