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;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-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Tue Dec 5 18:18:39 CET 2017
From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
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@xxxxxxxxxx>
[ 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@xxxxxxxxxx>
Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Naveen N . Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Cc: Paul E . McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/150845661962.5443.17724352636247312231.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
queue-3.18/kprobes-use-synchronize_rcu_tasks-for-optprobe-with-config_preempt-y.patch