From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H . Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH -tip v2] kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT
Date: Mon, 11 Sep 2017 21:04:35 -0700 [thread overview]
Message-ID: <20170912040435.GS3521@linux.vnet.ibm.com> (raw)
In-Reply-To: <150517865165.26279.7811625865051741769.stgit@devbox>
On Tue, Sep 12, 2017 at 10:10:51AM +0900, Masami Hiramatsu wrote:
> To enable jump optimized probe with CONFIG_PREEMPT, use
> synchronize_rcu_tasks() to wait for all tasks preempted
> on trampoline code back on track.
>
> Since the jump optimized kprobes can replace multiple
> instructions, there can be tasks which are interrupted
> on the 2nd (or 3rd) instructions. If the kprobe
> replaces those instructions by a jump instruction,
> when those tasks back to the interrupted place, it is
> a middle of the jump instruction and causes a kernel
> panic.
> To avoid such tragedies in advance, kprobe optimizer
> prepare a detour route using normal kprobe (e.g.
> int3 breakpoint on x86), and wait for the tasks which
> is interrrupted on such place by synchronize_sched()
> when CONFIG_PREEMPT=n.
> If CONFIG_PREEMPT=y, things be more complicated, because
> such interrupted thread can be preempted (other thread
> can be scheduled in interrupt handler.) So, kprobes
> optimizer has to wait for those tasks scheduled normally.
> In this case we can use synchronize_rcu_tasks() which
> ensures that all preempted tasks back on track and
> schedule it.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
> arch/Kconfig | 2 +-
> kernel/kprobes.c | 18 +++++++++++++-----
> 2 files changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 2520ca5b42eb..d495c06ae961 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -90,7 +90,7 @@ config STATIC_KEYS_SELFTEST
> config OPTPROBES
> def_bool y
> depends on KPROBES && HAVE_OPTPROBES
> - depends on !PREEMPT
> + select TASKS_RCU if PREEMPT
>
> config KPROBES_ON_FTRACE
> def_bool y
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index a1606a4224e1..6243b8b02511 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -574,12 +574,20 @@ static void kprobe_optimizer(struct work_struct *work)
>
> /*
> * Step 2: Wait for quiesence period to ensure all running interrupts
> - * are done. Because optprobe may modify multiple instructions
> - * there is a chance that Nth instruction is interrupted. In that
> - * case, running interrupt can return to 2nd-Nth byte of jump
> - * instruction. This wait is for avoiding it.
> + * are done. Because optprobe may modify multiple instructions,
> + * there is a chance that the Nth instruction is interrupted. In that
> + * case, running interrupt can return to the Nth byte of jump
> + * instruction. This can be avoided by waiting for returning of
> + * such interrupts, since (until here) the first byte of the optimized
> + * probe is already replaced with normal kprobe (sw breakpoint) and
> + * all threads which reach to the probed address will hit it and
> + * bypass the copied instructions instead of executing the original.
> + * With CONFIG_PREEMPT, such interrupts can be preepmted. To wait
> + * for such thread, we will use synchronize_rcu_tasks() which ensures
> + * all preeempted tasks are scheduled normally (= not preempted.)
> + * So we can ensure there is no threads preempted at probed address.
> */
> - synchronize_sched();
> + synchronize_rcu_tasks();
>
> /* Step 3: Optimize kprobes after quiesence period */
> do_optimize_kprobes();
>
next prev parent reply other threads:[~2017-09-12 5:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-12 1:10 [PATCH -tip v2] Enable optprobe on preepmtive kernel Masami Hiramatsu
2017-09-12 1:10 ` [PATCH -tip v2] kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT Masami Hiramatsu
2017-09-12 4:04 ` Paul E. McKenney [this message]
2017-09-14 4:28 ` [lkp-robot] [kprobes] e1ce3eee7d: BUG:using_smp_processor_id()in_preemptible kernel test robot
2017-09-14 10:22 ` Masami Hiramatsu
2017-09-15 0:12 ` Masami Hiramatsu
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