linux-kernel - Re: [PATCH v4 04/17] context_tracking: Add ct_state and CT_WARN

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Date:	Tue, 30 Jun 2015 14:20:47 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Kees Cook <keescook@...omium.org>,
	Brian Gerst <brgerst@...il.com>, paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH v4 04/17] context_tracking: Add ct_state and CT_WARN_ON

On Mon, Jun 29, 2015 at 12:33:36PM -0700, Andy Lutomirski wrote:
> This will let us sprinkle sanity checks around the kernel without
> making too much of a mess.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  include/linux/context_tracking.h       | 15 +++++++++++++++
>  include/linux/context_tracking_state.h |  1 +
>  2 files changed, 16 insertions(+)
> 
> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
> index b96bd299966f..008fc67d0d96 100644
> --- a/include/linux/context_tracking.h
> +++ b/include/linux/context_tracking.h
> @@ -49,13 +49,28 @@ static inline void exception_exit(enum ctx_state prev_ctx)
>  	}
>  }
>  
> +
> +/**
> + * ct_state() - return the current context tracking state if known
> + *
> + * Returns the current cpu's context tracking state if context tracking

			 CPU's

> + * is enabled.  If context tracking is disabled, returns
> + * CONTEXT_DISABLED.  This should be used primarily for debugging.
> + */
> +static inline enum ctx_state ct_state(void)
> +{
> +	return context_tracking_is_enabled() ?
> +		this_cpu_read(context_tracking.state) : CONTEXT_DISABLED;
> +}
>  #else
>  static inline void user_enter(void) { }
>  static inline void user_exit(void) { }
>  static inline enum ctx_state exception_enter(void) { return 0; }
>  static inline void exception_exit(enum ctx_state prev_ctx) { }
> +static inline enum ctx_state ct_state(void) { return CONTEXT_DISABLED; }
>  #endif /* !CONFIG_CONTEXT_TRACKING */
>  
> +#define CT_WARN_ON(cond) WARN_ON(context_tracking_is_enabled() && (cond))

Btw, that "CT_" prefix makes this look like it is the software
controlling this thing:

https://upload.wikimedia.org/wikipedia/commons/thumb/2/27/UPMCEast_CTscan.jpg/1280px-UPMCEast_CTscan.jpg

:-)

Other kernel code uses "cxt" or "ctxt" abbreviations. Maybe

	CTXT_WARN_ON(cond)

...

>  #ifdef CONFIG_CONTEXT_TRACKING_FORCE
>  extern void context_tracking_init(void);
> diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> index 678ecdf90cf6..ee956c528fab 100644
> --- a/include/linux/context_tracking_state.h
> +++ b/include/linux/context_tracking_state.h
> @@ -14,6 +14,7 @@ struct context_tracking {
>  	bool active;
>  	int recursion;
>  	enum ctx_state {
> +		CONTEXT_DISABLED = -1,	/* returned by ct_state() if unknown */
>  		CONTEXT_KERNEL = 0,
>  		CONTEXT_USER,
>  		CONTEXT_GUEST,

And those then CTXT_*

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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