linux-kernel - Re: [PATCH] drm: avoid switching to text console if there is no panic timeout

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Message-ID: <CABqxG0eKhaGUMvdNMOdahnqdYiT8i+3Hhf8vbQyq8TEJUOU0Lg@mail.gmail.com>
Date:	Tue, 18 Oct 2011 10:19:42 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
	Hugh Dickins <hughd@...omium.org>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Airlie <airlied@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm: avoid switching to text console if there is no panic timeout

On Tue, Oct 18, 2011 at 8:06 AM, Mandeep Singh Baines <msb@...omium.org> wrote:
> From: Hugh Dickins <hughd@...omium.org>
>
> Add a check for panic_timeout in the drm_fb_helper_panic() notifier: if
> we're going to reboot immediately, the user will not be able to see the
> messages anyway, and messing with the video mode may display artifacts,
> and certainly get into several layers of complexity (including mutexes and
> memory allocations) which we shall be much safer to avoid.

There's one exception is use printk_delay

>
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> [ Edited commit message and modified to short-circuit panic_timeout < 0
>  instead of testing panic_timeout >= 0.  -Mandeep ]
> Signed-off-by: Mandeep Singh Baines <msb@...omium.org>
> Cc: Dave Airlie <airlied@...hat.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: dri-devel@...ts.freedesktop.org
> ---
>  drivers/gpu/drm/drm_fb_helper.c |    7 +++++++
>  1 files changed, 7 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index f7c6854..0e62c93 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -254,6 +254,13 @@ bool drm_fb_helper_force_kernel_mode(void)
>  int drm_fb_helper_panic(struct notifier_block *n, unsigned long ununsed,
>                        void *panic_str)
>  {
> +       /*
> +        * It's a waste of time and effort to switch back to text console
> +        * if the kernel should reboot before panic messages can be seen.
> +        */
> +       if (panic_timeout < 0)
> +               return 0;
> +
>        printk(KERN_ERR "panic occurred, switching back to text console\n");
>        return drm_fb_helper_force_kernel_mode();
>  }
> --
> 1.7.3.1
>
> --
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-- 
Regards
Dave
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