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Subject: Re: [PATCH v1.1] drm/rockchip: fix race with kms hotplug and fbdev
To: Mark Yao <mark.yao@rock-chips.com>, David Airlie <airlied@linux.ie>,
        Heiko Stuebner <heiko@sntech.de>
Cc: linux-rockchip@lists.infradead.org,
        linux-arm-kernel@lists.infradead.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <1501494601-7140-1-git-send-email-mark.yao@rock-chips.com>
 <1501575103-20136-1-git-send-email-mark.yao@rock-chips.com>
From: Sandy Huang <sandy.huang@rock-chips.com>
Message-ID: <3084b854-1b82-5a72-ad51-f7b12e5a57a0@rock-chips.com>
Date: Fri, 4 Aug 2017 11:20:25 +0800
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Hi Mark,

在 2017/8/1 16:11, Mark Yao 写道:
> According to the kerneldoc[0], should do fbdev setup before calling
> drm_kms_helper_poll_init(), otherwise, Kms hotplug event may race
> into fbdev helper initial, and fb_helper->dev may be NULL pointer,
> that would cause the bug:
> [    0.735411] [00000200] *pgd=00000000f6ffe003, *pud=00000000f6ffe003, *pmd=0000000000000000
> [    0.736156] Internal error: Oops: 96000005 [#1] PREEMPT SMP
> [    0.736648] Modules linked in:
> [    0.736930] CPU: 2 PID: 20 Comm: kworker/2:0 Not tainted 4.4.41 #20
> [    0.737480] Hardware name: Rockchip RK3399 Board rev2 (BOX) (DT)
> [    0.738020] Workqueue: events cdn_dp_pd_event_work
> [    0.738447] task: ffffffc0f21f3100 ti: ffffffc0f2218000 task.ti: ffffffc0f2218000
> [    0.739109] PC is at mutex_lock+0x14/0x44
> [    0.739469] LR is at drm_fb_helper_hotplug_event+0x30/0x114
> [    0.756253] [<ffffff8008a344f4>] mutex_lock+0x14/0x44
> [    0.756260] [<ffffff8008445708>] drm_fb_helper_hotplug_event+0x30/0x114
> [    0.756271] [<ffffff8008473c84>] rockchip_drm_output_poll_changed+0x18/0x20
> [    0.756280] [<ffffff8008439fcc>] drm_kms_helper_hotplug_event+0x28/0x34
> [    0.756286] [<ffffff800846c444>] cdn_dp_pd_event_work+0x394/0x3c4
> [    0.756295] [<ffffff80080b2b38>] process_one_work+0x218/0x3e0
> [    0.756302] [<ffffff80080b3538>] worker_thread+0x2e8/0x404
> [    0.756308] [<ffffff80080b7e70>] kthread+0xe8/0xf0
> [    0.756316] [<ffffff8008082690>] ret_from_fork+0x10/0x40
> 
> [0]: https://01.org/linuxgraphics/gfx-docs/drm/gpu/drm-kms-helpers.html
> 
> Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
> ---
> Changes in v1.1:
> - According to the kerneldoc, fix the race bug in generic way.
> 
>   drivers/gpu/drm/rockchip/rockchip_drm_drv.c | 13 ++++++-------
>   1 file changed, 6 insertions(+), 7 deletions(-)
> 
Reviewed-by: Sandy huang <sandy.huang@rock-chips.com>