Regression in panic

From: Mandeep Singh Baines
Date: Mon Jun 20 2011 - 18:15:47 EST

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On Tue, Jun 22, 2010 at 8:12 PM, Dave Airlie <airlied@xxxxxxxxx> wrote:
> 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>

Hi Dave,

I think this change is causing a regression I'm seeing in panic.
Before this change, I'd get a
reboot on panic (we've configured as such).

With this change, my machine gets wedged if the machine is running in
X when the panic occurs.

I traced the code flow to this:

bust_spinlocks(0);
->unblank_screen();
->do_unblank_screen(0);
->vc->vc_sw->con_blank(vc, 0, 0);
->fbcon_blank(vc, 0, 0);
->update_screen(vc);
->redraw_screen(vc, 0);
->vc->vc_sw->con_switch(vc);
->fbcon_switch(vc);
->ops->update_start(info);
->bit_update_start(info);
->fb_pan_display(info, &ops->var);
->info->fbops->fb_pan_display(var, info);
->drm_fb_helper_pan_display(var, info);
->mutex_lock(&dev->mode_config.mutex); *this blocks*

With this change, there is now a lot going on in the panic path. Stuff
that I'm not sure is safe when panicking. In addition to the
mutex_lock, there is also a del_timer_sync()
now happening in the context of panic().

I see this bug with a 2.6.38 kernel but did a quick scan of a newer
kernels and did not see anything that changed in this path so I
suspect its still there.

Reverting this change fixes the regression.

Regards,
Mandeep

> ---
> 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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Next message: Jeremy Fitzhardinge: "[PATCH 14/15] xen/multicall: special-case singleton hypercalls"
Previous message: Jeremy Fitzhardinge: "[PATCH 10/15] xen/mmu: use extend_args for more mmuext updates"
Next in thread: David Rientjes: "Re: Regression in panic"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]