linux-kernel - Re: [PATCH v7 1/2] printk: add interface for disabling recursion check

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Date:	Thu, 7 Jun 2012 13:19:16 +0000
From:	bing deng <deng8bing@...il.com>
To:	shuox.liu@...el.com
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>,
	"Luck, Tony" <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH v7 1/2] printk: add interface for disabling recursion check

On Thu, Jun 7, 2012 at 2:57 AM, ShuoX Liu <shuox.liu@...el.com> wrote:
> From: ShuoX Liu <shuox.liu@...el.com>
>
> With some special scenario, such as Machine Check Exception happened
> in printk, we want to bypass printk recursion check to printk some
> important information. So we add these interfaces of printk.
>
> 1) printk_recursion_check_disable() for disabling recursion check
> 2) printk_recursion_check_enable() for enabling recursion check
>
> Signed-off-by: Yanmin Zhang <yanmin_zhang@...ux.intel.com>
> Signed-off-by: ShuoX Liu <shuox.liu@...el.com>
> ---
>  include/linux/printk.h |    3 +++
>  kernel/printk.c        |   17 ++++++++++++++++-
>  2 files changed, 19 insertions(+), 1 deletions(-)
>
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index 1bec2f7..da48ec7 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -42,6 +42,9 @@ static inline void console_verbose(void)
>                console_loglevel = 15;
>  }
>
> +void printk_recursion_check_disable(void);
> +void printk_recursion_check_enable(void);
> +
>  struct va_format {
>        const char *fmt;
>        va_list *va;
> diff --git a/kernel/printk.c b/kernel/printk.c
> index 32462d2..0580f67 100644
> --- a/kernel/printk.c
> +++ b/kernel/printk.c
> @@ -78,6 +78,19 @@ int console_printk[4] = {
>  int oops_in_progress;
>  EXPORT_SYMBOL(oops_in_progress);
>
> +static atomic_t recursion_check_disabled = ATOMIC_INIT(0);
> +
> +void printk_recursion_check_disable(void)
> +{
> +       atomic_inc(&recursion_check_disabled);
> +}
> +
> +void printk_recursion_check_enable(void)
> +{
> +       WARN_ON(atomic_read(&recursion_check_disabled) < 1);
> +       atomic_dec(&recursion_check_disabled);
> +}
> +
>  /*
>  * console_sem protects the console_drivers list, and also
>  * provides serialisation for access to the entire console
> @@ -1295,7 +1308,9 @@ asmlinkage int vprintk_emit(int facility, int level,
>                 * recursion and return - but flag the recursion so that
>                 * it can be printed at the next appropriate moment:
>                 */
> -               if (!oops_in_progress && !lockdep_recursing(current)) {
> +               if (!atomic_read(&recursion_check_disabled)
> +                       && !oops_in_progress
> +                       && !lockdep_recursing(current)) {
>                        recursion_bug = 1;
>                        goto out_restore_irqs;
>                }
> --
> 1.7.1
>
> --
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Hi Shuo,

    Should the two function be export by EXPORT_SYMBOL? The the other
module can use it.

-- 
Best Regards,
Bing
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