[Linux-stable-mirror] Patch "kprobes: Use synchronize_rcu_tasks() for optprobe with CONFIG_PREEMPT=y" has been added to the 3.18-stable tree
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 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-3.18 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 Tue Dec 5 18:18:39 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 @@ -74,7 +74,7 @@ config JUMP_LABEL 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 @@ -540,13 +540,15 @@ 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-3.18/kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
Hi Greg,
On Tue, 05 Dec 2017 18:30:54 +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=yto the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-3.18 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 is not for bugfix, but improvement. And also, it depends on TASKS_RCU & commit 7e42776d5ed1fe9a941ed8876c5d15cd7cf5d89f.
So, please don't pull it on stable tree.
Thank you,
From foo@baz Tue Dec 5 18:18:39 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 @@ -74,7 +74,7 @@ config JUMP_LABEL 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 @@ -540,13 +540,15 @@ 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-3.18/kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch
On Thu, Dec 07, 2017 at 08:27:37AM +0900, Masami Hiramatsu wrote:
Hi Greg,
On Tue, 05 Dec 2017 18:30:54 +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=yto the 3.18-stable tree which can be found at: https://urldefense.proofpoint.com/v2/url?u=http-3A__www.kernel.org_git_-3Fp-...
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-3.18 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 is not for bugfix, but improvement. And also, it depends on TASKS_RCU & commit 7e42776d5ed1fe9a941ed8876c5d15cd7cf5d89f.
So, please don't pull it on stable tree.
Thanks for the clarification.
Just to help me understand this better, what I understood from the patch is that we might execute freed trampoline memory, is that not the case here?
On Wed, 6 Dec 2017 23:37:50 +0000 alexander.levin@verizon.com wrote:
On Thu, Dec 07, 2017 at 08:27:37AM +0900, Masami Hiramatsu wrote:
Hi Greg,
On Tue, 05 Dec 2017 18:30:54 +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=yto the 3.18-stable tree which can be found at: https://urldefense.proofpoint.com/v2/url?u=http-3A__www.kernel.org_git_-3Fp-...
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-3.18 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 is not for bugfix, but improvement. And also, it depends on TASKS_RCU & commit 7e42776d5ed1fe9a941ed8876c5d15cd7cf5d89f.
So, please don't pull it on stable tree.
Thanks for the clarification.
Just to help me understand this better, what I understood from the patch is that we might execute freed trampoline memory, is that not the case here?
No, the patch is only for PREEMPT kernel. Without the patch, PREEMPT kernel disables optprobe itself. On the other hand, non preempt kernel enables optprobe but it uses synchronize_sched() for waiting quiesense period, so that all interrupt routines are done and optprobe can free the trampoline memory safely.
Note that non preempt kernel doesn't preempt tasks, it only interrupts tasks and return soon (without task switching). But PREEMPT kernel can preempt a task, this means a task can be interrupted and switched to other task on the way of execution on trampoline memory. This requires synchronize_rcu_tasks() to wait for switching back to the preempted tasks.
The commit 7e42776d5ed exposes synchronize_rcu_tasks() as a alias of synchronize_sched() when PREEMPT=n.
Thank you,
On Thu, Dec 07, 2017 at 02:54:58PM +0900, Masami Hiramatsu wrote:
On Wed, 6 Dec 2017 23:37:50 +0000 alexander.levin@verizon.com wrote:
On Thu, Dec 07, 2017 at 08:27:37AM +0900, Masami Hiramatsu wrote:
Hi Greg,
On Tue, 05 Dec 2017 18:30:54 +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=yto the 3.18-stable tree which can be found at: https://urldefense.proofpoint.com/v2/url?u=http-3A__www.kernel.org_git_-3Fp-...
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-3.18 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 is not for bugfix, but improvement. And also, it depends on TASKS_RCU & commit 7e42776d5ed1fe9a941ed8876c5d15cd7cf5d89f.
So, please don't pull it on stable tree.
Thanks for the clarification.
Just to help me understand this better, what I understood from the patch is that we might execute freed trampoline memory, is that not the case here?
No, the patch is only for PREEMPT kernel. Without the patch, PREEMPT kernel disables optprobe itself. On the other hand, non preempt kernel enables optprobe but it uses synchronize_sched() for waiting quiesense period, so that all interrupt routines are done and optprobe can free the trampoline memory safely.
Note that non preempt kernel doesn't preempt tasks, it only interrupts tasks and return soon (without task switching). But PREEMPT kernel can preempt a task, this means a task can be interrupted and switched to other task on the way of execution on trampoline memory. This requires synchronize_rcu_tasks() to wait for switching back to the preempted tasks.
The commit 7e42776d5ed exposes synchronize_rcu_tasks() as a alias of synchronize_sched() when PREEMPT=n.
Thank you,
Thank you for the explanation Masami!
-- Masami Hiramatsu mhiramat@kernel.org
On Thu, Dec 07, 2017 at 08:27:37AM +0900, Masami Hiramatsu wrote:
Hi Greg,
On Tue, 05 Dec 2017 18:30:54 +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=yto the 3.18-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
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-3.18 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 is not for bugfix, but improvement. And also, it depends on TASKS_RCU & commit 7e42776d5ed1fe9a941ed8876c5d15cd7cf5d89f.
So, please don't pull it on stable tree.
Ok, now dropped from the 3.18 stable tree, thanks.
greg k-h
linux-stable-mirror@lists.linaro.org
-
alexander.levin＠verizon.com -
Greg KH -
gregkh＠linuxfoundation.org
-
Masami Hiramatsu