linux-kernel - Re: [RFC][PATCH v2] drm: kirin: Add a mutex to avoid fb initialization race

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Date:   Fri, 24 Feb 2017 17:52:40 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     liuxinliang <z.liuxinliang@...ilicon.com>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Rongrong Zou <zourongrong@...il.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Chen Feng <puck.chen@...ilicon.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sean Paul <seanpaul@...omium.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [RFC][PATCH v2] drm: kirin: Add a mutex to avoid fb
 initialization race

On Fri, Feb 24, 2017 at 5:45 PM, liuxinliang
<z.liuxinliang@...ilicon.com> wrote:
>
>
> On 2017/2/25 9:39, liuxinliang wrote:
>>
>> Hi John,
>>
>> The patch seems good to me, except one minus comment.
>> Maybe change fb_lock to fbdev_lock would be better.
>>
>> Thanks,
>> -xinliang
>>
>> On 2017/2/25 9:25, John Stultz wrote:
>>>
>>> In some cases I've been seeing a race where two framebuffers
>>> would be initialized, as kirin_fbdev_output_poll_changed()
>>> might get called quickly in succession, resulting in the
>>> initialization happening twice. This could cause the system
>>> to boot up with a blank screen.
>>>
>>> This patch adds a simple mutex to serialize it and seems to
>>> avoid the race.
>>>
>>> Suggestions or feedback would be greatly appreciated!
>>>
>>> Cc: Xinliang Liu <z.liuxinliang@...ilicon.com>
>>> Cc: Rongrong Zou <zourongrong@...il.com>
>>> Cc: Xinwei Kong <kong.kongxinwei@...ilicon.com>
>>> Cc: Chen Feng <puck.chen@...ilicon.com>
>>> Cc: David Airlie <airlied@...ux.ie>
>>> Cc: Daniel Vetter <daniel.vetter@...ll.ch>
>>> Cc: Sean Paul <seanpaul@...omium.org>
>>> Cc: dri-devel@...ts.freedesktop.org
>>> Signed-off-by: John Stultz <john.stultz@...aro.org>
>>> ---
>>>   drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c | 4 ++++
>>>   drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.h | 1 +
>>>   2 files changed, 5 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
>>> b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
>>> index 7ec93ae..b83556a 100644
>>> --- a/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
>>> +++ b/drivers/gpu/drm/hisilicon/kirin/kirin_drm_drv.c
>>> @@ -55,6 +55,7 @@ static void kirin_fbdev_output_poll_changed(struct
>>> drm_device *dev)
>>>   {
>>>       struct kirin_drm_private *priv = dev->dev_private;
>>>   +    mutex_lock(&priv->fb_lock);
>>>       if (priv->fbdev) {
>>>           drm_fbdev_cma_hotplug_event(priv->fbdev);
>>>       } else {
>>> @@ -63,6 +64,7 @@ static void kirin_fbdev_output_poll_changed(struct
>>> drm_device *dev)
>>>           if (IS_ERR(priv->fbdev))
>>>               priv->fbdev = NULL;
>>>       }
>>> +    mutex_unlock(&priv->fb_lock);
>>>   }
>>>   #endif
>>>   @@ -95,6 +97,8 @@ static int kirin_drm_kms_init(struct drm_device *dev)
>>>       if (!priv)
>>>           return -ENOMEM;
>>>   +    mutex_init(&priv->fb_lock);
>
> And put this line in CONFIG_DRM_FBDEV_EMULATION


Ok. Done! Thanks again for the review and feedback!
-john