Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1650204 > unrolled thread

Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for optprobe wit CONFIG_PREEMPT

Started byIngo Molnar <mingo@kernel.org>
First post2017-05-25 08:20 +0200
Last post2017-05-26 17:50 +0200
Articles 6 — 3 participants

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for  optprobe wit CONFIG_PREEMPT Ingo Molnar <mingo@kernel.org> - 2017-05-25 08:20 +0200
    Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for  optprobe wit CONFIG_PREEMPT Masami Hiramatsu <mhiramat@kernel.org> - 2017-05-25 11:10 +0200
    Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for  optprobe wit CONFIG_PREEMPT "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-25 17:20 +0200
      Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for  optprobe wit CONFIG_PREEMPT Masami Hiramatsu <mhiramat@kernel.org> - 2017-05-26 03:20 +0200
      Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for  optprobe wit CONFIG_PREEMPT Ingo Molnar <mingo@kernel.org> - 2017-05-26 08:20 +0200
        Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for  optprobe wit CONFIG_PREEMPT "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-05-26 17:50 +0200

#1650204 — Re: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for optprobe wit CONFIG_PREEMPT

FromIngo Molnar <mingo@kernel.org>
Date2017-05-25 08:20 +0200
SubjectRe: [RFC PATCH tip/master] kprobes: Use synchronize_rcu_tasks() for optprobe wit CONFIG_PREEMPT
Message-ID<tKUhQ-4zw-5@gated-at.bofh.it>
* Masami Hiramatsu <mhiramat@kernel.org> wrote:

> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -377,6 +377,23 @@ static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p)
>  static bool kprobes_allow_optimization;
>  
>  /*
> + * Synchronizing wait on trampline code for interrupted tasks/threads.
> + * Since the threads running on dynamically allocated trampline code
> + * can be interrupted, kprobes has to wait for those tasks back on
> + * track and scheduled. If the kernel is preemptive, the thread can be
> + * preempted by other tasks on the trampoline too. For such case, this
> + * calls synchronize_rcu_tasks() to wait for those tasks back on track.
> + */
> +static void synchronize_on_trampoline(void)
> +{
> +#ifdef CONFIG_PREEMPT
> +	synchronize_rcu_tasks();
> +#else
> +	synchronize_sched();
> +#endif
> +}

So that's really unacceptably ugly.

Paul, I still question the need to have tasks-RCU as a Kconfig distinction, 
_especially_ if its API usage results in such ugly secondary #ifdefs...

Why isn't there a single synchronize_rcu_tasks() API function, which does what is 
expected, where the _RCU_ code figures out how to implement it?

I.e.:

 - There should be no user configurable TASKS_RCU Kconfig setting - at most a
   helper Kconfig that is automatically selected by the RCU code itself.

 - Both ftrace andkprobes would use a simple synchronize_rcu_tasks() call.

Thanks,

	Ingo

[toc] | [next] | [standalone]

#1650337

FromMasami Hiramatsu <mhiramat@kernel.org>
Date2017-05-25 11:10 +0200
Message-ID<tKWWl-6hJ-1@gated-at.bofh.it>
In reply to#1650204
On Thu, 25 May 2017 08:15:55 +0200
Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -377,6 +377,23 @@ static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p)
> >  static bool kprobes_allow_optimization;
> >  
> >  /*
> > + * Synchronizing wait on trampline code for interrupted tasks/threads.
> > + * Since the threads running on dynamically allocated trampline code
> > + * can be interrupted, kprobes has to wait for those tasks back on
> > + * track and scheduled. If the kernel is preemptive, the thread can be
> > + * preempted by other tasks on the trampoline too. For such case, this
> > + * calls synchronize_rcu_tasks() to wait for those tasks back on track.
> > + */
> > +static void synchronize_on_trampoline(void)
> > +{
> > +#ifdef CONFIG_PREEMPT
> > +	synchronize_rcu_tasks();
> > +#else
> > +	synchronize_sched();
> > +#endif
> > +}
> 
> So that's really unacceptably ugly.
> 
> Paul, I still question the need to have tasks-RCU as a Kconfig distinction, 
> _especially_ if its API usage results in such ugly secondary #ifdefs...
> 
> Why isn't there a single synchronize_rcu_tasks() API function, which does what is 
> expected, where the _RCU_ code figures out how to implement it?

Hmm, if there are only 3 users, kprobes/ftrace/kpatch, and those
use it same purpose (wait for tasks which preempted or interrupted),
maybe we can switch the implementation of synchronize_rcu_tasks()
in RCU level.

> 
> I.e.:
> 
>  - There should be no user configurable TASKS_RCU Kconfig setting - at most a
>    helper Kconfig that is automatically selected by the RCU code itself.

TASKS_RCU kconfig is already a hidden setting. It is selected if
CONFIG_PREEMPT=y && CONFIG_KPROBES=y && HAVE_OPTPROBES=y for kprobes.

Thank you,

> 
>  - Both ftrace andkprobes would use a simple synchronize_rcu_tasks() call.


-- 
Masami Hiramatsu <mhiramat@kernel.org>

[toc] | [prev] | [next] | [standalone]

#1650579

From"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date2017-05-25 17:20 +0200
Message-ID<tL2Iq-1qK-25@gated-at.bofh.it>
In reply to#1650204
On Thu, May 25, 2017 at 08:15:55AM +0200, Ingo Molnar wrote:
> 
> * Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > --- a/kernel/kprobes.c
> > +++ b/kernel/kprobes.c
> > @@ -377,6 +377,23 @@ static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p)
> >  static bool kprobes_allow_optimization;
> >  
> >  /*
> > + * Synchronizing wait on trampline code for interrupted tasks/threads.
> > + * Since the threads running on dynamically allocated trampline code
> > + * can be interrupted, kprobes has to wait for those tasks back on
> > + * track and scheduled. If the kernel is preemptive, the thread can be
> > + * preempted by other tasks on the trampoline too. For such case, this
> > + * calls synchronize_rcu_tasks() to wait for those tasks back on track.
> > + */
> > +static void synchronize_on_trampoline(void)
> > +{
> > +#ifdef CONFIG_PREEMPT
> > +	synchronize_rcu_tasks();
> > +#else
> > +	synchronize_sched();
> > +#endif
> > +}
> 
> So that's really unacceptably ugly.
> 
> Paul, I still question the need to have tasks-RCU as a Kconfig distinction, 
> _especially_ if its API usage results in such ugly secondary #ifdefs...
> 
> Why isn't there a single synchronize_rcu_tasks() API function, which does what is 
> expected, where the _RCU_ code figures out how to implement it?
> 
> I.e.:
> 
>  - There should be no user configurable TASKS_RCU Kconfig setting - at most a
>    helper Kconfig that is automatically selected by the RCU code itself.
> 
>  - Both ftrace andkprobes would use a simple synchronize_rcu_tasks() call.
> 
> Thanks,

How about the following (untested) patch?

This is against -rcu's rcu/dev branch, FWIW.

And I am also queuing patches with other cleanups, including do_exit(),
enabled by this approach.

							Thanx, Paul

------------------------------------------------------------------------

commit 9ab47fba45cea06e223e524d392621b64c174720
Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date:   Thu May 25 08:05:00 2017 -0700

    rcu: Drive TASKS_RCU directly off of PREEMPT
    
    The actual use of TASKS_RCU is only when PREEMPT, otherwise RCU-sched
    is used instead.  This commit therefore makes synchronize_rcu_tasks()
    and call_rcu_tasks() available always, but mapped to synchronize_sched()
    and call_rcu_sched(), respectively, when !PREEMPT.  This approach also
    allows some #ifdefs to be removed from rcutorture.
    
    Reported-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

---

 include/linux/rcupdate.h |    6 ++++--
 kernel/rcu/Kconfig       |    3 +--
 kernel/rcu/rcutorture.c  |   17 +----------------
 3 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index f816fc72b51e..c3f380befdd7 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -58,8 +58,6 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func);
 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func);
 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func);
 void synchronize_sched(void);
-void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
-void synchronize_rcu_tasks(void);
 void rcu_barrier_tasks(void);
 
 #ifdef CONFIG_PREEMPT_RCU
@@ -176,10 +174,14 @@ extern struct srcu_struct tasks_rcu_exit_srcu;
 		rcu_all_qs(); \
 		rcu_note_voluntary_context_switch_lite(t); \
 	} while (0)
+void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
+void synchronize_rcu_tasks(void);
 #else /* #ifdef CONFIG_TASKS_RCU */
 #define TASKS_RCU(x) do { } while (0)
 #define rcu_note_voluntary_context_switch_lite(t)	do { } while (0)
 #define rcu_note_voluntary_context_switch(t)		rcu_all_qs()
+#define call_rcu_tasks call_rcu_sched
+#define synchronize_rcu_tasks synchronize_sched
 #endif /* #else #ifdef CONFIG_TASKS_RCU */
 
 /**
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index be90c945063f..9210379c0353 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -69,8 +69,7 @@ config TREE_SRCU
 	  This option selects the full-fledged version of SRCU.
 
 config TASKS_RCU
-	bool
-	default n
+	def_bool PREEMPT
 	select SRCU
 	help
 	  This option enables a task-based RCU implementation that uses
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index aedc8f2ad955..273032dc8f2d 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -659,8 +659,6 @@ static struct rcu_torture_ops sched_ops = {
 	.name		= "sched"
 };
 
-#ifdef CONFIG_TASKS_RCU
-
 /*
  * Definitions for RCU-tasks torture testing.
  */
@@ -698,24 +696,11 @@ static struct rcu_torture_ops tasks_ops = {
 	.name		= "tasks"
 };
 
-#define RCUTORTURE_TASKS_OPS &tasks_ops,
-
 static bool __maybe_unused torturing_tasks(void)
 {
 	return cur_ops == &tasks_ops;
 }
 
-#else /* #ifdef CONFIG_TASKS_RCU */
-
-#define RCUTORTURE_TASKS_OPS
-
-static bool __maybe_unused torturing_tasks(void)
-{
-	return false;
-}
-
-#endif /* #else #ifdef CONFIG_TASKS_RCU */
-
 /*
  * RCU torture priority-boost testing.  Runs one real-time thread per
  * CPU for moderate bursts, repeatedly registering RCU callbacks and
@@ -1712,7 +1697,7 @@ rcu_torture_init(void)
 	int firsterr = 0;
 	static struct rcu_torture_ops *torture_ops[] = {
 		&rcu_ops, &rcu_bh_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,
-		&sched_ops, RCUTORTURE_TASKS_OPS
+		&sched_ops, &tasks_ops,
 	};
 
 	if (!torture_init_begin(torture_type, verbose, &torture_runnable))

[toc] | [prev] | [next] | [standalone]

#1651020

FromMasami Hiramatsu <mhiramat@kernel.org>
Date2017-05-26 03:20 +0200
Message-ID<tLc54-7AA-7@gated-at.bofh.it>
In reply to#1650579
On Thu, 25 May 2017 08:14:01 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> On Thu, May 25, 2017 at 08:15:55AM +0200, Ingo Molnar wrote:
> > 
> > * Masami Hiramatsu <mhiramat@kernel.org> wrote:
> > 
> > > --- a/kernel/kprobes.c
> > > +++ b/kernel/kprobes.c
> > > @@ -377,6 +377,23 @@ static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p)
> > >  static bool kprobes_allow_optimization;
> > >  
> > >  /*
> > > + * Synchronizing wait on trampline code for interrupted tasks/threads.
> > > + * Since the threads running on dynamically allocated trampline code
> > > + * can be interrupted, kprobes has to wait for those tasks back on
> > > + * track and scheduled. If the kernel is preemptive, the thread can be
> > > + * preempted by other tasks on the trampoline too. For such case, this
> > > + * calls synchronize_rcu_tasks() to wait for those tasks back on track.
> > > + */
> > > +static void synchronize_on_trampoline(void)
> > > +{
> > > +#ifdef CONFIG_PREEMPT
> > > +	synchronize_rcu_tasks();
> > > +#else
> > > +	synchronize_sched();
> > > +#endif
> > > +}
> > 
> > So that's really unacceptably ugly.
> > 
> > Paul, I still question the need to have tasks-RCU as a Kconfig distinction, 
> > _especially_ if its API usage results in such ugly secondary #ifdefs...
> > 
> > Why isn't there a single synchronize_rcu_tasks() API function, which does what is 
> > expected, where the _RCU_ code figures out how to implement it?
> > 
> > I.e.:
> > 
> >  - There should be no user configurable TASKS_RCU Kconfig setting - at most a
> >    helper Kconfig that is automatically selected by the RCU code itself.
> > 
> >  - Both ftrace andkprobes would use a simple synchronize_rcu_tasks() call.
> > 
> > Thanks,
> 
> How about the following (untested) patch?

This patch is good to me for kprobes at least.

Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>

Steve, how about ftrace usage?

Thank you,

> 
> This is against -rcu's rcu/dev branch, FWIW.
> 
> And I am also queuing patches with other cleanups, including do_exit(),
> enabled by this approach.
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> commit 9ab47fba45cea06e223e524d392621b64c174720
> Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Date:   Thu May 25 08:05:00 2017 -0700
> 
>     rcu: Drive TASKS_RCU directly off of PREEMPT
>     
>     The actual use of TASKS_RCU is only when PREEMPT, otherwise RCU-sched
>     is used instead.  This commit therefore makes synchronize_rcu_tasks()
>     and call_rcu_tasks() available always, but mapped to synchronize_sched()
>     and call_rcu_sched(), respectively, when !PREEMPT.  This approach also
>     allows some #ifdefs to be removed from rcutorture.
>     
>     Reported-by: Ingo Molnar <mingo@kernel.org>
>     Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> ---
> 
>  include/linux/rcupdate.h |    6 ++++--
>  kernel/rcu/Kconfig       |    3 +--
>  kernel/rcu/rcutorture.c  |   17 +----------------
>  3 files changed, 6 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index f816fc72b51e..c3f380befdd7 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -58,8 +58,6 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func);
>  void call_rcu_bh(struct rcu_head *head, rcu_callback_t func);
>  void call_rcu_sched(struct rcu_head *head, rcu_callback_t func);
>  void synchronize_sched(void);
> -void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
> -void synchronize_rcu_tasks(void);
>  void rcu_barrier_tasks(void);
>  
>  #ifdef CONFIG_PREEMPT_RCU
> @@ -176,10 +174,14 @@ extern struct srcu_struct tasks_rcu_exit_srcu;
>  		rcu_all_qs(); \
>  		rcu_note_voluntary_context_switch_lite(t); \
>  	} while (0)
> +void call_rcu_tasks(struct rcu_head *head, rcu_callback_t func);
> +void synchronize_rcu_tasks(void);
>  #else /* #ifdef CONFIG_TASKS_RCU */
>  #define TASKS_RCU(x) do { } while (0)
>  #define rcu_note_voluntary_context_switch_lite(t)	do { } while (0)
>  #define rcu_note_voluntary_context_switch(t)		rcu_all_qs()
> +#define call_rcu_tasks call_rcu_sched
> +#define synchronize_rcu_tasks synchronize_sched
>  #endif /* #else #ifdef CONFIG_TASKS_RCU */
>  
>  /**
> diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
> index be90c945063f..9210379c0353 100644
> --- a/kernel/rcu/Kconfig
> +++ b/kernel/rcu/Kconfig
> @@ -69,8 +69,7 @@ config TREE_SRCU
>  	  This option selects the full-fledged version of SRCU.
>  
>  config TASKS_RCU
> -	bool
> -	default n
> +	def_bool PREEMPT
>  	select SRCU
>  	help
>  	  This option enables a task-based RCU implementation that uses
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index aedc8f2ad955..273032dc8f2d 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -659,8 +659,6 @@ static struct rcu_torture_ops sched_ops = {
>  	.name		= "sched"
>  };
>  
> -#ifdef CONFIG_TASKS_RCU
> -
>  /*
>   * Definitions for RCU-tasks torture testing.
>   */
> @@ -698,24 +696,11 @@ static struct rcu_torture_ops tasks_ops = {
>  	.name		= "tasks"
>  };
>  
> -#define RCUTORTURE_TASKS_OPS &tasks_ops,
> -
>  static bool __maybe_unused torturing_tasks(void)
>  {
>  	return cur_ops == &tasks_ops;
>  }
>  
> -#else /* #ifdef CONFIG_TASKS_RCU */
> -
> -#define RCUTORTURE_TASKS_OPS
> -
> -static bool __maybe_unused torturing_tasks(void)
> -{
> -	return false;
> -}
> -
> -#endif /* #else #ifdef CONFIG_TASKS_RCU */
> -
>  /*
>   * RCU torture priority-boost testing.  Runs one real-time thread per
>   * CPU for moderate bursts, repeatedly registering RCU callbacks and
> @@ -1712,7 +1697,7 @@ rcu_torture_init(void)
>  	int firsterr = 0;
>  	static struct rcu_torture_ops *torture_ops[] = {
>  		&rcu_ops, &rcu_bh_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,
> -		&sched_ops, RCUTORTURE_TASKS_OPS
> +		&sched_ops, &tasks_ops,
>  	};
>  
>  	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
> 


-- 
Masami Hiramatsu <mhiramat@kernel.org>

[toc] | [prev] | [next] | [standalone]

#1651098

FromIngo Molnar <mingo@kernel.org>
Date2017-05-26 08:20 +0200
Message-ID<tLgLn-2gD-5@gated-at.bofh.it>
In reply to#1650579
* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:

> How about the following (untested) patch?

Looks good to me!

Acked-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo

[toc] | [prev] | [next] | [standalone]

#1651441

From"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date2017-05-26 17:50 +0200
Message-ID<tLpF0-7Hk-15@gated-at.bofh.it>
In reply to#1651098
On Fri, May 26, 2017 at 08:10:25AM +0200, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> 
> > How about the following (untested) patch?
> 
> Looks good to me!
> 
> Acked-by: Ingo Molnar <mingo@kernel.org>

Very good, I have applied Masami's Reviewed-by and your Acked-by,
thank you both!

							Thanx, Paul

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web