[PATCH tracing/kprobes] kprobes: Disable booster when CONFIG_PREEMPT=y

[Masami Hiramatsu <mhiramat at redhat dot com>]

Disable kprobe booster when CONFIG_PREEMPT=y, because it can't ensure
that all kernel threads preempted on kprobe's boosted slot run out from
the slot even using freeze_processes().

The booster on preemptive kernel will be resumed if synchronize_tasks()
or something like that is introduced.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jim Keniston <jkenisto@us.ibm.com>
CC: Mathieu Desnoyers <compudj@krystal.dyndns.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
---

 arch/ia64/kernel/kprobes.c |    2 +-
 arch/x86/kernel/kprobes.c  |    2 +-
 kernel/kprobes.c           |   29 ++---------------------------
 3 files changed, 4 insertions(+), 29 deletions(-)

diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
index 9adac44..7026b29 100644
--- a/arch/ia64/kernel/kprobes.c
+++ b/arch/ia64/kernel/kprobes.c
@@ -870,7 +870,7 @@ static int __kprobes pre_kprobes_handler(struct die_args *args)
 		return 1;
 
 ss_probe:
-#if !defined(CONFIG_PREEMPT) || defined(CONFIG_FREEZER)
+#if !defined(CONFIG_PREEMPT)
 	if (p->ainsn.inst_flag == INST_FLAG_BOOSTABLE && !p->post_handler) {
 		/* Boost up -- we can execute copied instructions directly */
 		ia64_psr(regs)->ri = p->ainsn.slot;
diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 5b8c750..9453815 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -429,7 +429,7 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
 static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs,
 				       struct kprobe_ctlblk *kcb)
 {
-#if !defined(CONFIG_PREEMPT) || defined(CONFIG_FREEZER)
+#if !defined(CONFIG_PREEMPT)
 	if (p->ainsn.boostable == 1 && !p->post_handler) {
 		/* Boost up -- we can execute copied instructions directly */
 		reset_current_kprobe();
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index b7df302..9907a03 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -124,30 +124,6 @@ static LIST_HEAD(kprobe_insn_pages);
 static int kprobe_garbage_slots;
 static int collect_garbage_slots(void);
 
-static int __kprobes check_safety(void)
-{
-	int ret = 0;
-#if defined(CONFIG_PREEMPT) && defined(CONFIG_FREEZER)
-	ret = freeze_processes();
-	if (ret == 0) {
-		struct task_struct *p, *q;
-		do_each_thread(p, q) {
-			if (p != current && p->state == TASK_RUNNING &&
-			    p->pid != 0) {
-				printk("Check failed: %s is running\n",p->comm);
-				ret = -1;
-				goto loop_end;
-			}
-		} while_each_thread(p, q);
-	}
-loop_end:
-	thaw_processes();
-#else
-	synchronize_sched();
-#endif
-	return ret;
-}
-
 /**
  * __get_insn_slot() - Find a slot on an executable page for an instruction.
  * We allocate an executable page if there's no room on existing ones.
@@ -235,9 +211,8 @@ static int __kprobes collect_garbage_slots(void)
 {
 	struct kprobe_insn_page *kip, *next;
 
-	/* Ensure no-one is preepmted on the garbages */
-	if (check_safety())
-		return -EAGAIN;
+	/* Ensure no-one is interrupted on the garbages */
+	synchronize_sched();
 
 	list_for_each_entry_safe(kip, next, &kprobe_insn_pages, list) {
 		int i;


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com