[PATCH] drm/vkms: Fix flush_work() without INIT_WORK().

[Sean Paul]

On Sat, Jan 19, 2019 at 01:43:43AM +0900, Tetsuo Handa wrote:
> syzbot is hitting a lockdep warning [1] because flush_work() is called
> without INIT_WORK() after kzalloc() at vkms_atomic_crtc_reset().
> 
> Commit 6c234fe37c57627a ("drm/vkms: Implement CRC debugfs API") added
> INIT_WORK() to only vkms_atomic_crtc_duplicate_state() side. Assuming
> that lifecycle of crc_work is appropriately managed, fix this problem
> by adding INIT_WORK() to vkms_atomic_crtc_reset() side.
> 
> [1] https://syzkaller.appspot.com/bug?id=a5954455fcfa51c29ca2ab55b203076337e1c770
> 
> Reported-and-tested-by: syzbot <syzbot+12f1b031b6da017e34f8 at syzkaller.appspotmail.com>
> Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
> ---
>  drivers/gpu/drm/vkms/vkms_crtc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index 177bbcb..3c37d8c 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -104,6 +104,7 @@ static void vkms_atomic_crtc_reset(struct drm_crtc *crtc)
>  	vkms_state = kzalloc(sizeof(*vkms_state), GFP_KERNEL);
>  	if (!vkms_state)
>  		return;
> +	INIT_WORK(&vkms_state->crc_work, vkms_crc_work_handle);

Presumably we should migrate/duplicate the crc_work state from the old state
rather than just re-initializing? My context on the crc_work is foggy, but we
should be sure that either:

a) the existing crc work is flushed and inactive, or
b) we migrate the existing crc work to the duplicated state to keep track of it

Sean

>  
>  	crtc->state = &vkms_state->base;
>  	crtc->state->crtc = crtc;
> -- 
> 1.8.3.1
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS