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SubjectRe: [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@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)
>



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