kprobes: introduce ftrace based optimization
Introduce function trace based kprobes optimization.
With using ftrace optimization, kprobes on the mcount calling
address, use ftrace's mcount call instead of breakpoint.
Furthermore, this optimization works with preemptive kernel
not like as current jump-based optimization. Of cource,
this feature works only if the probe is on mcount call.
Only if kprobe.break_handler is set, that probe is not
optimized with ftrace (nor put on ftrace). The reason why this
limitation comes is that this break_handler may be used only
from jprobes which changes ip address (for fetching the function
arguments), but function tracer ignores modified ip address.
Changes in v2:
- Fix ftrace_ops registering right after setting its filter.
- Unregister ftrace_ops if there is no kprobe using.
- Remove notrace dependency from __kprobes macro.
Link: http://lkml.kernel.org/r/20120605102832.27845.63461.stgit@localhost.localdomain
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: "Frank Ch. Eigler" <fche@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 9e47f44..69c16ef 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -759,6 +759,10 @@
struct kprobe *ap;
struct optimized_kprobe *op;
+ /* Impossible to optimize ftrace-based kprobe */
+ if (kprobe_ftrace(p))
+ return;
+
/* For preparing optimization, jump_label_text_reserved() is called */
jump_label_lock();
mutex_lock(&text_mutex);
@@ -915,9 +919,64 @@
}
#endif /* CONFIG_OPTPROBES */
+#ifdef KPROBES_CAN_USE_FTRACE
+static struct ftrace_ops kprobe_ftrace_ops __read_mostly = {
+ .regs_func = kprobe_ftrace_handler,
+ .flags = FTRACE_OPS_FL_SAVE_REGS,
+};
+static int kprobe_ftrace_enabled;
+
+/* Must ensure p->addr is really on ftrace */
+static int __kprobes prepare_kprobe(struct kprobe *p)
+{
+ if (!kprobe_ftrace(p))
+ return arch_prepare_kprobe(p);
+
+ return arch_prepare_kprobe_ftrace(p);
+}
+
+/* Caller must lock kprobe_mutex */
+static void __kprobes arm_kprobe_ftrace(struct kprobe *p)
+{
+ int ret;
+
+ ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
+ (unsigned long)p->addr, 0, 0);
+ WARN(ret < 0, "Failed to arm kprobe-ftrace at %p (%d)\n", p->addr, ret);
+ kprobe_ftrace_enabled++;
+ if (kprobe_ftrace_enabled == 1) {
+ ret = register_ftrace_function(&kprobe_ftrace_ops);
+ WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret);
+ }
+}
+
+/* Caller must lock kprobe_mutex */
+static void __kprobes disarm_kprobe_ftrace(struct kprobe *p)
+{
+ int ret;
+
+ kprobe_ftrace_enabled--;
+ if (kprobe_ftrace_enabled == 0) {
+ ret = unregister_ftrace_function(&kprobe_ftrace_ops);
+ WARN(ret < 0, "Failed to init kprobe-ftrace (%d)\n", ret);
+ }
+ ret = ftrace_set_filter_ip(&kprobe_ftrace_ops,
+ (unsigned long)p->addr, 1, 0);
+ WARN(ret < 0, "Failed to disarm kprobe-ftrace at %p (%d)\n", p->addr, ret);
+}
+#else /* !KPROBES_CAN_USE_FTRACE */
+#define prepare_kprobe(p) arch_prepare_kprobe(p)
+#define arm_kprobe_ftrace(p) do {} while (0)
+#define disarm_kprobe_ftrace(p) do {} while (0)
+#endif
+
/* Arm a kprobe with text_mutex */
static void __kprobes arm_kprobe(struct kprobe *kp)
{
+ if (unlikely(kprobe_ftrace(kp))) {
+ arm_kprobe_ftrace(kp);
+ return;
+ }
/*
* Here, since __arm_kprobe() doesn't use stop_machine(),
* this doesn't cause deadlock on text_mutex. So, we don't
@@ -929,11 +988,15 @@
}
/* Disarm a kprobe with text_mutex */
-static void __kprobes disarm_kprobe(struct kprobe *kp)
+static void __kprobes disarm_kprobe(struct kprobe *kp, bool reopt)
{
+ if (unlikely(kprobe_ftrace(kp))) {
+ disarm_kprobe_ftrace(kp);
+ return;
+ }
/* Ditto */
mutex_lock(&text_mutex);
- __disarm_kprobe(kp, true);
+ __disarm_kprobe(kp, reopt);
mutex_unlock(&text_mutex);
}
@@ -1343,6 +1406,26 @@
struct module **probed_mod)
{
int ret = 0;
+ unsigned long ftrace_addr;
+
+ /*
+ * If the address is located on a ftrace nop, set the
+ * breakpoint to the following instruction.
+ */
+ ftrace_addr = ftrace_location((unsigned long)p->addr);
+ if (ftrace_addr) {
+#ifdef KPROBES_CAN_USE_FTRACE
+ /* Given address is not on the instruction boundary */
+ if ((unsigned long)p->addr != ftrace_addr)
+ return -EILSEQ;
+ /* break_handler (jprobe) can not work with ftrace */
+ if (p->break_handler)
+ return -EINVAL;
+ p->flags |= KPROBE_FLAG_FTRACE;
+#else /* !KPROBES_CAN_USE_FTRACE */
+ return -EINVAL;
+#endif
+ }
jump_label_lock();
preempt_disable();
@@ -1350,7 +1433,6 @@
/* Ensure it is not in reserved area nor out of text */
if (!kernel_text_address((unsigned long) p->addr) ||
in_kprobes_functions((unsigned long) p->addr) ||
- ftrace_text_reserved(p->addr, p->addr) ||
jump_label_text_reserved(p->addr, p->addr)) {
ret = -EINVAL;
goto out;
@@ -1422,7 +1504,7 @@
}
mutex_lock(&text_mutex); /* Avoiding text modification */
- ret = arch_prepare_kprobe(p);
+ ret = prepare_kprobe(p);
mutex_unlock(&text_mutex);
if (ret)
goto out;
@@ -1480,7 +1562,7 @@
/* Try to disarm and disable this/parent probe */
if (p == orig_p || aggr_kprobe_disabled(orig_p)) {
- disarm_kprobe(orig_p);
+ disarm_kprobe(orig_p, true);
orig_p->flags |= KPROBE_FLAG_DISABLED;
}
}
@@ -2078,10 +2160,11 @@
if (!pp)
pp = p;
- seq_printf(pi, "%s%s%s\n",
+ seq_printf(pi, "%s%s%s%s\n",
(kprobe_gone(p) ? "[GONE]" : ""),
((kprobe_disabled(p) && !kprobe_gone(p)) ? "[DISABLED]" : ""),
- (kprobe_optimized(pp) ? "[OPTIMIZED]" : ""));
+ (kprobe_optimized(pp) ? "[OPTIMIZED]" : ""),
+ (kprobe_ftrace(pp) ? "[FTRACE]" : ""));
}
static void __kprobes *kprobe_seq_start(struct seq_file *f, loff_t *pos)
@@ -2160,14 +2243,12 @@
goto already_enabled;
/* Arming kprobes doesn't optimize kprobe itself */
- mutex_lock(&text_mutex);
for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
head = &kprobe_table[i];
hlist_for_each_entry_rcu(p, node, head, hlist)
if (!kprobe_disabled(p))
- __arm_kprobe(p);
+ arm_kprobe(p);
}
- mutex_unlock(&text_mutex);
kprobes_all_disarmed = false;
printk(KERN_INFO "Kprobes globally enabled\n");
@@ -2195,15 +2276,13 @@
kprobes_all_disarmed = true;
printk(KERN_INFO "Kprobes globally disabled\n");
- mutex_lock(&text_mutex);
for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
head = &kprobe_table[i];
hlist_for_each_entry_rcu(p, node, head, hlist) {
if (!arch_trampoline_kprobe(p) && !kprobe_disabled(p))
- __disarm_kprobe(p, false);
+ disarm_kprobe(p, false);
}
}
- mutex_unlock(&text_mutex);
mutex_unlock(&kprobe_mutex);
/* Wait for disarming all kprobes by optimizer */
