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Re: [PATCH -tip v8 09/26] x86: Call exception_enter after kprobes handled
- From: Steven Rostedt <rostedt at goodmis dot org>
- To: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>
- Cc: linux-kernel at vger dot kernel dot org, Ingo Molnar <mingo at kernel dot org>, Andi Kleen <andi at firstfloor dot org>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Sandeepa Prabhu <sandeepa dot prabhu at linaro dot org>, Frederic Weisbecker <fweisbec at gmail dot com>, x86 at kernel dot org, fche at redhat dot com, mingo at redhat dot com, systemtap at sourceware dot org, "H. Peter Anvin" <hpa at zytor dot com>, Thomas Gleixner <tglx at linutronix dot de>
- Date: Mon, 24 Mar 2014 15:31:29 -0400
- Subject: Re: [PATCH -tip v8 09/26] x86: Call exception_enter after kprobes handled
- Authentication-results: sourceware.org; auth=none
- References: <20140305115843 dot 22766 dot 8355 dot stgit at ltc230 dot yrl dot intra dot hitachi dot co dot jp> <20140305115946 dot 22766 dot 73261 dot stgit at ltc230 dot yrl dot intra dot hitachi dot co dot jp>
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@goodmis.org>
-- Steve
On Wed, 05 Mar 2014 20:59:46 +0900
Masami Hiramatsu <masami.hiramatsu.pt@hitachi.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@hitachi.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)
>