Re: [PATCH] vt/console: try harder to print output when panicing

[James Simmons]

> From: Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>
> 
> Jesse's initial patch commit said:
> 
> "At panic time (i.e. when oops_in_progress is set) we should try a bit
> harder to update the screen and make sure output gets to the VT, since
> some drivers are capable of flipping back to it.
> 
> So make sure we try to unblank and update the display if called from a
> panic context."
> 
> I've enhanced this to add a flag to the vc that console layer can set
> to indicate they want this behaviour to occur. This also adds support
> to fbcon for that flag and adds an fb flag for drivers to indicate
> they want to use the support. It enables this for KMS drivers.
> 
> Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>

I really like the fact that the console driver has a flag to turn this on 
or off.

Signed-off-by: James Simmons <jsimmons@xxxxxxxxxxxxx>

> ---
>  drivers/char/vt.c                       |   13 +++++++++----
>  drivers/gpu/drm/i915/intel_fb.c         |    4 +---
>  drivers/gpu/drm/nouveau/nouveau_fbcon.c |    1 +
>  drivers/gpu/drm/radeon/radeon_fb.c      |    2 +-
>  drivers/video/console/fbcon.c           |    4 +++-
>  include/linux/console_struct.h          |    1 +
>  include/linux/fb.h                      |    4 ++++
>  include/linux/vt_kern.h                 |    7 +++++++
>  8 files changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/char/vt.c b/drivers/char/vt.c
> index 7cdb6ee..6e04c9e 100644
> --- a/drivers/char/vt.c
> +++ b/drivers/char/vt.c
> @@ -698,7 +698,10 @@ void redraw_screen(struct vc_data *vc, int is_switch)
>  			update_attr(vc);
>  			clear_buffer_attributes(vc);
>  		}
> -		if (update && vc->vc_mode != KD_GRAPHICS)
> +
> +		/* Forcibly update if we're panicing */
> +		if ((update && vc->vc_mode != KD_GRAPHICS) ||
> +		    vt_force_oops_output(vc))
>  			do_update_region(vc, vc->vc_origin, vc->vc_screenbuf_size / 2);
>  	}
>  	set_cursor(vc);
> @@ -736,6 +739,7 @@ static void visual_init(struct vc_data *vc, int num, int init)
>  	vc->vc_hi_font_mask = 0;
>  	vc->vc_complement_mask = 0;
>  	vc->vc_can_do_color = 0;
> +	vc->vc_panic_force_write = false;
>  	vc->vc_sw->con_init(vc, init);
>  	if (!vc->vc_complement_mask)
>  		vc->vc_complement_mask = vc->vc_can_do_color ? 0x7700 : 0x0800;
> @@ -2498,7 +2502,7 @@ static void vt_console_print(struct console *co, const char *b, unsigned count)
>  		goto quit;
>  	}
>  
> -	if (vc->vc_mode != KD_TEXT)
> +	if (vc->vc_mode != KD_TEXT && !vt_force_oops_output(vc))
>  		goto quit;
>  
>  	/* undraw cursor first */
> @@ -3703,7 +3707,8 @@ void do_unblank_screen(int leaving_gfx)
>  		return;
>  	}
>  	vc = vc_cons[fg_console].d;
> -	if (vc->vc_mode != KD_TEXT)
> +	/* Try to unblank in oops case too */
> +	if (vc->vc_mode != KD_TEXT && !vt_force_oops_output(vc))
>  		return; /* but leave console_blanked != 0 */
>  
>  	if (blankinterval) {
> @@ -3712,7 +3717,7 @@ void do_unblank_screen(int leaving_gfx)
>  	}
>  
>  	console_blanked = 0;
> -	if (vc->vc_sw->con_blank(vc, 0, leaving_gfx))
> +	if (vc->vc_sw->con_blank(vc, 0, leaving_gfx) || vt_force_oops_output(vc))
>  		/* Low-level driver cannot restore -> do it ourselves */
>  		update_screen(vc);
>  	if (console_blank_hook)
> diff --git a/drivers/gpu/drm/i915/intel_fb.c b/drivers/gpu/drm/i915/intel_fb.c
> index c3c5052..bd5d87a 100644
> --- a/drivers/gpu/drm/i915/intel_fb.c
> +++ b/drivers/gpu/drm/i915/intel_fb.c
> @@ -128,7 +128,7 @@ static int intelfb_create(struct intel_fbdev *ifbdev,
>  
>  	strcpy(info->fix.id, "inteldrmfb");
>  
> -	info->flags = FBINFO_DEFAULT;
> +	info->flags = FBINFO_DEFAULT | FBINFO_CAN_FORCE_OUTPUT;
>  	info->fbops = &intelfb_ops;
>  
>  	/* setup aperture base/size for vesafb takeover */
> @@ -146,8 +146,6 @@ static int intelfb_create(struct intel_fbdev *ifbdev,
>  	info->fix.smem_start = dev->mode_config.fb_base + obj_priv->gtt_offset;
>  	info->fix.smem_len = size;
>  
> -	info->flags = FBINFO_DEFAULT;
> -
>  	info->screen_base = ioremap_wc(dev->agp->base + obj_priv->gtt_offset,
>  				       size);
>  	if (!info->screen_base) {
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fbcon.c b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> index c9a4a0d..9b2d3b7 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
> @@ -250,6 +250,7 @@ nouveau_fbcon_create(struct nouveau_fbdev *nfbdev,
>  		info->flags = FBINFO_DEFAULT | FBINFO_HWACCEL_COPYAREA |
>  			      FBINFO_HWACCEL_FILLRECT |
>  			      FBINFO_HWACCEL_IMAGEBLIT;
> +	info->flags |= FBINFO_CAN_FORCE_OUTPUT;
>  	info->fbops = &nouveau_fbcon_ops;
>  	info->fix.smem_start = dev->mode_config.fb_base + nvbo->bo.offset -
>  			       dev_priv->vm_vram_base;
> diff --git a/drivers/gpu/drm/radeon/radeon_fb.c b/drivers/gpu/drm/radeon/radeon_fb.c
> index dc1634b..dbf8696 100644
> --- a/drivers/gpu/drm/radeon/radeon_fb.c
> +++ b/drivers/gpu/drm/radeon/radeon_fb.c
> @@ -224,7 +224,7 @@ static int radeonfb_create(struct radeon_fbdev *rfbdev,
>  
>  	drm_fb_helper_fill_fix(info, fb->pitch, fb->depth);
>  
> -	info->flags = FBINFO_DEFAULT;
> +	info->flags = FBINFO_DEFAULT | FBINFO_CAN_FORCE_OUTPUT;
>  	info->fbops = &radeonfb_ops;
>  
>  	tmp = radeon_bo_gpu_offset(rbo) - rdev->mc.vram_start;
> diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
> index b0a3fa0..7eadb35 100644
> --- a/drivers/video/console/fbcon.c
> +++ b/drivers/video/console/fbcon.c
> @@ -283,7 +283,8 @@ static inline int fbcon_is_inactive(struct vc_data *vc, struct fb_info *info)
>  	struct fbcon_ops *ops = info->fbcon_par;
>  
>  	return (info->state != FBINFO_STATE_RUNNING ||
> -		vc->vc_mode != KD_TEXT || ops->graphics);
> +		vc->vc_mode != KD_TEXT || ops->graphics) &&
> +		!vt_force_oops_output(vc);
>  }
>  
>  static inline int get_color(struct vc_data *vc, struct fb_info *info,
> @@ -1073,6 +1074,7 @@ static void fbcon_init(struct vc_data *vc, int init)
>  	if (p->userfont)
>  		charcnt = FNTCHARCNT(p->fontdata);
>  
> +	vc->vc_panic_force_write = !!(info->flags & FBINFO_CAN_FORCE_OUTPUT);
>  	vc->vc_can_do_color = (fb_get_color_depth(&info->var, &info->fix)!=1);
>  	vc->vc_complement_mask = vc->vc_can_do_color ? 0x7700 : 0x0800;
>  	if (charcnt == 256) {
> diff --git a/include/linux/console_struct.h b/include/linux/console_struct.h
> index 38fe59d..d7d9acd 100644
> --- a/include/linux/console_struct.h
> +++ b/include/linux/console_struct.h
> @@ -105,6 +105,7 @@ struct vc_data {
>  	struct vc_data **vc_display_fg;		/* [!] Ptr to var holding fg console for this display */
>  	unsigned long	vc_uni_pagedir;
>  	unsigned long	*vc_uni_pagedir_loc;  /* [!] Location of uni_pagedir variable for this console */
> +	bool vc_panic_force_write; /* when oops/panic this VC can accept forced output/blanking */
>  	/* additional information is in vt_kern.h */
>  };
>  
> diff --git a/include/linux/fb.h b/include/linux/fb.h
> index 8e5a9df..25f4950 100644
> --- a/include/linux/fb.h
> +++ b/include/linux/fb.h
> @@ -812,6 +812,10 @@ struct fb_tile_ops {
>   */
>  #define FBINFO_BE_MATH  0x100000
>  
> +/* report to the VT layer that this fb driver can accept forced console
> +   output like oopses */
> +#define FBINFO_CAN_FORCE_OUTPUT     0x200000
> +
>  struct fb_info {
>  	int node;
>  	int flags;
> diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
> index 7f56db4..56cce34 100644
> --- a/include/linux/vt_kern.h
> +++ b/include/linux/vt_kern.h
> @@ -100,6 +100,13 @@ extern int unbind_con_driver(const struct consw *csw, int first, int last,
>  			     int deflt);
>  int vty_init(const struct file_operations *console_fops);
>  
> +static inline bool vt_force_oops_output(struct vc_data *vc)
> +{
> +	if (oops_in_progress && vc->vc_panic_force_write)
> +		return true;
> +	return false;
> +}
> +
>  /*
>   * vc_screen.c shares this temporary buffer with the console write code so that
>   * we can easily avoid touching user space while holding the console spinlock.
> -- 
> 1.7.1
> 
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