Patch "kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y" has been added to the 4.14-stable tree

Patch "kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y" has been added to the 4.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Dec  6 18:04:41 CET 2017
From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Fri, 20 Oct 2017 08:43:39 +0900
Subject: kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y

From: Masami Hiramatsu <mhiramat@kernel.org>


[ Upstream commit a30b85df7d599f626973e9cd3056fe755bd778e0 ]

We want to wait for all potentially preempted kprobes trampoline
execution to have completed. This guarantees that any freed
trampoline memory is not in use by any task in the system anymore.
synchronize_rcu_tasks() gives such a guarantee, so use it.

Also, this guarantees to wait for all potentially preempted tasks
on the instructions which will be replaced with a jump.

Since this becomes a problem only when CONFIG_PREEMPT=y, enable
CONFIG_TASKS_RCU=y for synchronize_rcu_tasks() in that case.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Naveen N . Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/150845661962.5443.17724352636247312231.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/Kconfig     |    2 +-
 kernel/kprobes.c |   14 ++++++++------
 2 files changed, 9 insertions(+), 7 deletions(-)

--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -91,7 +91,7 @@ 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
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -573,13 +573,15 @@ static void kprobe_optimizer(struct work
 	do_unoptimize_kprobes();
 
 	/*
-	 * 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.
+	 * Step 2: Wait for quiesence period to ensure all potentially
+	 * preempted tasks to have normally scheduled. Because optprobe
+	 * may modify multiple instructions, there is a chance that Nth
+	 * instruction is preempted. In that case, such tasks can return
+	 * to 2nd-Nth byte of jump instruction. This wait is for avoiding it.
+	 * Note that on non-preemptive kernel, this is transparently converted
+	 * to synchronoze_sched() to wait for all interrupts to have completed.
 	 */
-	synchronize_sched();
+	synchronize_rcu_tasks();
 
 	/* Step 3: Optimize kprobes after quiesence period */
 	do_optimize_kprobes();


Patches currently in stable-queue which might be from mhiramat@kernel.org are

queue-4.14/kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
queue-4.14/kprobes-x86-disable-preemption-in-ftrace-based-jprobes.patch

Re: Patch "kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y" has been added to the 4.14-stable tree

[Naveen N. Rao]

Hi Greg,

gregkh@linuxfoundation.org wrote:
> 
> This is a note to let you know that I've just added the patch titled
> 
>     kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y
> 
> to the 4.14-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
> and it can be found in the queue-4.14 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.

Can you please also add the below two patches for v4.14-stable tree? The 
below patches address some issues that arise on powerpc due to this 
patch:
commit 6baea433bc84 (powerpc/jprobes: Disable preemption when triggered 
through ftrace)
commit 8a2d71a3f273 (powerpc/kprobes: Disable preemption before invoking 
probe handler for optprobes)

They apply on the stable-v4.14.y tree without any changes.


Thanks,
Naveen

Re: Patch "kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y" has been added to the 4.14-stable tree

[Masami Hiramatsu]

On Wed, 06 Dec 2017 18:25:55 +0100
<gregkh@linuxfoundation.org> wrote:

> 
> This is a note to let you know that I've just added the patch titled
> 
>     kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y
> 
> to the 4.14-stable tree which can be found at:
>     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> 
> The filename of the patch is:
>      kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
> and it can be found in the queue-4.14 subdirectory.
> 
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.

this depends on
commit 7e42776d5ed1f ("rcu: Drive TASKS_RCU directly off of PREEMPT")

So, pull above commit too, for 4.14 and 4.9. But I'm not sure TASKS_RCU is
introduced on 3.18.

Thank you,

> 
> 
> From foo@baz Wed Dec  6 18:04:41 CET 2017
> From: Masami Hiramatsu <mhiramat@kernel.org>
> Date: Fri, 20 Oct 2017 08:43:39 +0900
> Subject: kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y
> 
> From: Masami Hiramatsu <mhiramat@kernel.org>
> 
> 
> [ Upstream commit a30b85df7d599f626973e9cd3056fe755bd778e0 ]
> 
> We want to wait for all potentially preempted kprobes trampoline
> execution to have completed. This guarantees that any freed
> trampoline memory is not in use by any task in the system anymore.
> synchronize_rcu_tasks() gives such a guarantee, so use it.
> 
> Also, this guarantees to wait for all potentially preempted tasks
> on the instructions which will be replaced with a jump.
> 
> Since this becomes a problem only when CONFIG_PREEMPT=y, enable
> CONFIG_TASKS_RCU=y for synchronize_rcu_tasks() in that case.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Naveen N . Rao <naveen.n.rao@linux.vnet.ibm.com>
> Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Link: http://lkml.kernel.org/r/150845661962.5443.17724352636247312231.stgit@devbox
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  arch/Kconfig     |    2 +-
>  kernel/kprobes.c |   14 ++++++++------
>  2 files changed, 9 insertions(+), 7 deletions(-)
> 
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -91,7 +91,7 @@ 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
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -573,13 +573,15 @@ static void kprobe_optimizer(struct work
>  	do_unoptimize_kprobes();
>  
>  	/*
> -	 * 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.
> +	 * Step 2: Wait for quiesence period to ensure all potentially
> +	 * preempted tasks to have normally scheduled. Because optprobe
> +	 * may modify multiple instructions, there is a chance that Nth
> +	 * instruction is preempted. In that case, such tasks can return
> +	 * to 2nd-Nth byte of jump instruction. This wait is for avoiding it.
> +	 * Note that on non-preemptive kernel, this is transparently converted
> +	 * to synchronoze_sched() to wait for all interrupts to have completed.
>  	 */
> -	synchronize_sched();
> +	synchronize_rcu_tasks();
>  
>  	/* Step 3: Optimize kprobes after quiesence period */
>  	do_optimize_kprobes();
> 
> 
> Patches currently in stable-queue which might be from mhiramat@kernel.org are
> 
> queue-4.14/kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
> queue-4.14/kprobes-x86-disable-preemption-in-ftrace-based-jprobes.patch


-- 
Masami Hiramatsu <mhiramat@kernel.org>

Re: Patch "kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y" has been added to the 4.14-stable tree

[Greg KH]

On Thu, Dec 07, 2017 at 08:34:56AM +0900, Masami Hiramatsu wrote:
> On Wed, 06 Dec 2017 18:25:55 +0100
> <gregkh@linuxfoundation.org> wrote:
> 
> > 
> > This is a note to let you know that I've just added the patch titled
> > 
> >     kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y
> > 
> > to the 4.14-stable tree which can be found at:
> >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > 
> > The filename of the patch is:
> >      kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
> > and it can be found in the queue-4.14 subdirectory.
> > 
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@vger.kernel.org> know about it.
> 
> this depends on
> commit 7e42776d5ed1f ("rcu: Drive TASKS_RCU directly off of PREEMPT")

That patch is already in 4.14, so all should be fine there.

> So, pull above commit too, for 4.14 and 4.9. But I'm not sure TASKS_RCU is
> introduced on 3.18.

I've dropped this from 3.18 for now, and I'll go drop it from 4.9 as I
don't think it's really worth it at this point in time.

thanks for the review and quick response.

greg k-h

Re: Patch "kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y" has been added to the 4.14-stable tree

[Greg KH]

On Thu, Dec 07, 2017 at 01:46:08AM +0530, Naveen N. Rao wrote:
> Hi Greg,
> 
> gregkh@linuxfoundation.org wrote:
> > 
> > This is a note to let you know that I've just added the patch titled
> > 
> >     kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y
> > 
> > to the 4.14-stable tree which can be found at:
> >     http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
> > 
> > The filename of the patch is:
> >      kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
> > and it can be found in the queue-4.14 subdirectory.
> > 
> > If you, or anyone else, feels it should not be added to the stable tree,
> > please let <stable@vger.kernel.org> know about it.
> 
> Can you please also add the below two patches for v4.14-stable tree? The
> below patches address some issues that arise on powerpc due to this patch:
> commit 6baea433bc84 (powerpc/jprobes: Disable preemption when triggered
> through ftrace)
> commit 8a2d71a3f273 (powerpc/kprobes: Disable preemption before invoking
> probe handler for optprobes)
> 
> They apply on the stable-v4.14.y tree without any changes.

Thanks for the information, both patches now queued up.

greg k-h