linux-kernel - Re: [PATCH -tip v8 09/26] x86: Call exception

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Date:	Mon, 24 Mar 2014 15:31:29 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
	Frederic Weisbecker <fweisbec@...il.com>, x86@...nel.org,
	fche@...hat.com, mingo@...hat.com, systemtap@...rceware.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH -tip v8 09/26] x86: Call exception_enter after kprobes
 handled

Frederic,

This one's for you.

Looks good as the exception_enter() is to catch when userspace causes
the exception which wouldn't be the case for kprobes. When kprobes
needs to do work, it would have already been in the kernel and the
NO_HZ_FULL and RCU should be aware of that.

But for me:

Reviewed-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve


On Wed, 05 Mar 2014 20:59:46 +0900
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> wrote:

> Move exception_enter() call after kprobes handler
> is done. Since the exception_enter() involves
> many other functions (like printk), it can cause
> recursive int3/break loop when kprobes probe such
> functions.
> 
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> ---
>  arch/x86/kernel/traps.c |    5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index e5d4a70..ba9abe9 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -327,7 +327,6 @@ dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_co
>  	if (poke_int3_handler(regs))
>  		return;
>  
> -	prev_state = exception_enter();
>  #ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
>  	if (kgdb_ll_trap(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
>  				SIGTRAP) == NOTIFY_STOP)
> @@ -338,6 +337,7 @@ dotraplinkage void __kprobes notrace do_int3(struct pt_regs *regs, long error_co
>  	if (kprobe_int3_handler(regs))
>  		return;
>  #endif
> +	prev_state = exception_enter();
>  
>  	if (notify_die(DIE_INT3, "int3", regs, error_code, X86_TRAP_BP,
>  			SIGTRAP) == NOTIFY_STOP)
> @@ -415,8 +415,6 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
>  	unsigned long dr6;
>  	int si_code;
>  
> -	prev_state = exception_enter();
> -
>  	get_debugreg(dr6, 6);
>  
>  	/* Filter out all the reserved bits which are preset to 1 */
> @@ -449,6 +447,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
>  	if (kprobe_debug_handler(regs))
>  		goto exit;
>  #endif
> +	prev_state = exception_enter();
>  
>  	if (notify_die(DIE_DEBUG, "debug", regs, (long)&dr6, error_code,
>  							SIGTRAP) == NOTIFY_STOP)
> 

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