[PATCH] drm/fb-helper: don't sleep for screen unblank when an oopps is in progress

[Rob Clark]

On Sun, Jan 27, 2013 at 12:42 PM, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> Otherwise the system will burn even brighter and worse, leave the user
> wondering what's going on exactly.
>
> Since we already have a panic handler which will (try) to restore the
> entire fbdev console mode, we can just bail out. Inspired by a patch
> from Konstantin Khlebnikov. The callchain leading to this, cut&pasted
> from Konstantin's original patch:
>
> callstack:
> panic()
> bust_spinlocks(1)
> unblank_screen()
> vc->vc_sw->con_blank()
> fbcon_blank()
> fb_blank()
> info->fbops->fb_blank()
> drm_fb_helper_blank()
> drm_fb_helper_dpms()
> drm_modeset_lock_all()
> mutex_lock(&dev->mode_config.mutex)
>
> Note that the entire locking in the fb helper around panic/sysrq and
> kdbg is ... non-existant. So we have a decent change of blowing up
> everything. But since reworking this ties in with funny concepts like
> the fbdev notifier chain or the impressive things which happen around
> console_lock while oopsing, I'll leave that as an exercise for braver
> souls than me.
>
> v2: Drop the -EBUSY return value I've copied, we don't need it since
> the we'll take care of things ourselves anyway.
>
> Cc: Konstantin Khlebnikov <khlebnikov at openvz.org>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> References: https://patchwork.kernel.org/patch/1878181/
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Reviewed-by: Rob Clark <robdclark at gmail.com>

> ---
>  drivers/gpu/drm/drm_fb_helper.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index a7538cc..01099b5 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -386,6 +386,14 @@ static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
>         int i, j;
>
>         /*
> +        * fbdev->blank can be called from irq context in case of a panic.
> +        * Since we already have our own special panic handler which will
> +        * restore the fbdev console mode completely, just bail out early.
> +        */
> +       if (oops_in_progress)
> +               return;
> +
> +       /*
>          * For each CRTC in this fb, turn the connectors on/off.
>          */
>         drm_modeset_lock_all(dev);
> --
> 1.7.10.4
>
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