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Subject[PATCH 3/8] ftrace: Add enable/disable ftrace_ops control interface
Date
Adding a way to temporarily enable/disable ftrace_ops. The change
follows the same way as 'global' ftrace_ops are done.

Introducing 2 global ftrace_ops - control_ops and ftrace_control_list
which take over all ftrace_ops registered with FTRACE_OPS_FL_CONTROL
flag. In addition new per cpu flag called 'disabled' is also added to
ftrace_ops to provide the control information for each cpu.

When ftrace_ops with FTRACE_OPS_FL_CONTROL is registered, it is
set as disabled for all cpus.

The ftrace_control_list contains all the registered 'control' ftrace_ops.
The control_ops provides function which iterates ftrace_control_list
and does the check for 'disabled' flag on current cpu.

Adding 2 inline functions ftrace_function_enable/ftrace_function_disable,
which enable/disable the ftrace_ops for given cpu.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
---
include/linux/ftrace.h | 42 +++++++++++++++++
kernel/trace/ftrace.c | 116 +++++++++++++++++++++++++++++++++++++++++++++---
kernel/trace/trace.h | 2 +
3 files changed, 153 insertions(+), 7 deletions(-)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 523640f..67b8236 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -35,12 +35,14 @@ enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
FTRACE_OPS_FL_GLOBAL = 1 << 1,
FTRACE_OPS_FL_DYNAMIC = 1 << 2,
+ FTRACE_OPS_FL_CONTROL = 1 << 3,
};

struct ftrace_ops {
ftrace_func_t func;
struct ftrace_ops *next;
unsigned long flags;
+ void __percpu *disabled;
#ifdef CONFIG_DYNAMIC_FTRACE
struct ftrace_hash *notrace_hash;
struct ftrace_hash *filter_hash;
@@ -97,6 +99,46 @@ int register_ftrace_function(struct ftrace_ops *ops);
int unregister_ftrace_function(struct ftrace_ops *ops);
void clear_ftrace_function(void);

+/**
+ * ftrace_function_enable - enable controlled ftrace_ops on given cpu
+ *
+ * This function enables tracing on given cpu by decreasing
+ * the per cpu control variable.
+ * It must be called with preemption disabled and only on
+ * ftrace_ops registered with FTRACE_OPS_FL_CONTROL.
+ */
+static inline void ftrace_function_enable(struct ftrace_ops *ops, int cpu)
+{
+ atomic_t *disabled;
+
+ if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL)) ||
+ !preempt_count())
+ return;
+
+ disabled = per_cpu_ptr(ops->disabled, cpu);
+ atomic_dec(disabled);
+}
+
+/**
+ * ftrace_function_disable - enable controlled ftrace_ops on given cpu
+ *
+ * This function enables tracing on given cpu by decreasing
+ * the per cpu control variable.
+ * It must be called with preemption disabled and only on
+ * ftrace_ops registered with FTRACE_OPS_FL_CONTROL.
+ */
+static inline void ftrace_function_disable(struct ftrace_ops *ops, int cpu)
+{
+ atomic_t *disabled;
+
+ if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL)) ||
+ !preempt_count())
+ return;
+
+ disabled = per_cpu_ptr(ops->disabled, cpu);
+ atomic_inc(disabled);
+}
+
extern void ftrace_stub(unsigned long a0, unsigned long a1);

#else /* !CONFIG_FUNCTION_TRACER */
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7eb702f..1b56013 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -60,6 +60,8 @@
#define FTRACE_HASH_DEFAULT_BITS 10
#define FTRACE_HASH_MAX_BITS 12

+#define FL_GLOBAL_CONTROL (FTRACE_OPS_FL_GLOBAL | FTRACE_OPS_FL_CONTROL)
+
/* ftrace_enabled is a method to turn ftrace on or off */
int ftrace_enabled __read_mostly;
static int last_ftrace_enabled;
@@ -87,12 +89,14 @@ static struct ftrace_ops ftrace_list_end __read_mostly = {
};

static struct ftrace_ops *ftrace_global_list __read_mostly = &ftrace_list_end;
+static struct ftrace_ops *ftrace_control_list __read_mostly = &ftrace_list_end;
static struct ftrace_ops *ftrace_ops_list __read_mostly = &ftrace_list_end;
ftrace_func_t ftrace_trace_function __read_mostly = ftrace_stub;
static ftrace_func_t __ftrace_trace_function_delay __read_mostly = ftrace_stub;
ftrace_func_t __ftrace_trace_function __read_mostly = ftrace_stub;
ftrace_func_t ftrace_pid_function __read_mostly = ftrace_stub;
static struct ftrace_ops global_ops;
+static struct ftrace_ops control_ops;

static void
ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip);
@@ -166,6 +170,38 @@ static void ftrace_test_stop_func(unsigned long ip, unsigned long parent_ip)
}
#endif

+static void control_ops_disable_all(struct ftrace_ops *ops)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ atomic_set(per_cpu_ptr(ops->disabled, cpu), 1);
+}
+
+static int control_ops_alloc(struct ftrace_ops *ops)
+{
+ atomic_t *disabled;
+
+ disabled = alloc_percpu(atomic_t);
+ if (!disabled)
+ return -ENOMEM;
+
+ ops->disabled = disabled;
+ control_ops_disable_all(ops);
+ return 0;
+}
+
+static void control_ops_free(struct ftrace_ops *ops)
+{
+ free_percpu(ops->disabled);
+}
+
+static int control_ops_is_disabled(struct ftrace_ops *ops)
+{
+ atomic_t *disabled = this_cpu_ptr(ops->disabled);
+ return atomic_read(disabled);
+}
+
static void update_global_ops(void)
{
ftrace_func_t func;
@@ -257,6 +293,26 @@ static int remove_ftrace_ops(struct ftrace_ops **list, struct ftrace_ops *ops)
return 0;
}

+static void add_ftrace_list_ops(struct ftrace_ops **list,
+ struct ftrace_ops *main_ops,
+ struct ftrace_ops *ops)
+{
+ int first = *list == &ftrace_list_end;
+ add_ftrace_ops(list, ops);
+ if (first)
+ add_ftrace_ops(&ftrace_ops_list, main_ops);
+}
+
+static int remove_ftrace_list_ops(struct ftrace_ops **list,
+ struct ftrace_ops *main_ops,
+ struct ftrace_ops *ops)
+{
+ int ret = remove_ftrace_ops(list, ops);
+ if (!ret && *list == &ftrace_list_end)
+ ret = remove_ftrace_ops(&ftrace_ops_list, main_ops);
+ return ret;
+}
+
static int __register_ftrace_function(struct ftrace_ops *ops)
{
if (ftrace_disabled)
@@ -268,15 +324,19 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
if (WARN_ON(ops->flags & FTRACE_OPS_FL_ENABLED))
return -EBUSY;

+ if ((ops->flags & FL_GLOBAL_CONTROL) == FL_GLOBAL_CONTROL)
+ return -EINVAL;
+
if (!core_kernel_data((unsigned long)ops))
ops->flags |= FTRACE_OPS_FL_DYNAMIC;

if (ops->flags & FTRACE_OPS_FL_GLOBAL) {
- int first = ftrace_global_list == &ftrace_list_end;
- add_ftrace_ops(&ftrace_global_list, ops);
+ add_ftrace_list_ops(&ftrace_global_list, &global_ops, ops);
ops->flags |= FTRACE_OPS_FL_ENABLED;
- if (first)
- add_ftrace_ops(&ftrace_ops_list, &global_ops);
+ } else if (ops->flags & FTRACE_OPS_FL_CONTROL) {
+ if (control_ops_alloc(ops))
+ return -ENOMEM;
+ add_ftrace_list_ops(&ftrace_control_list, &control_ops, ops);
} else
add_ftrace_ops(&ftrace_ops_list, ops);

@@ -300,11 +360,23 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
return -EINVAL;

if (ops->flags & FTRACE_OPS_FL_GLOBAL) {
- ret = remove_ftrace_ops(&ftrace_global_list, ops);
- if (!ret && ftrace_global_list == &ftrace_list_end)
- ret = remove_ftrace_ops(&ftrace_ops_list, &global_ops);
+ ret = remove_ftrace_list_ops(&ftrace_global_list,
+ &global_ops, ops);
if (!ret)
ops->flags &= ~FTRACE_OPS_FL_ENABLED;
+ } else if (ops->flags & FTRACE_OPS_FL_CONTROL) {
+ ret = remove_ftrace_list_ops(&ftrace_control_list,
+ &control_ops, ops);
+ if (!ret) {
+ /*
+ * The ftrace_ops is now removed from the list,
+ * so there'll be no new users. We must ensure
+ * all current users are done before we free
+ * the control data.
+ */
+ synchronize_sched();
+ control_ops_free(ops);
+ }
} else
ret = remove_ftrace_ops(&ftrace_ops_list, ops);

@@ -3566,6 +3638,36 @@ ftrace_ops_test(struct ftrace_ops *ops, unsigned long ip)
#endif /* CONFIG_DYNAMIC_FTRACE */

static void
+ftrace_ops_control_func(unsigned long ip, unsigned long parent_ip)
+{
+ struct ftrace_ops *op;
+
+ if (unlikely(trace_recursion_test(TRACE_CONTROL_BIT)))
+ return;
+
+ /*
+ * Some of the ops may be dynamically allocated,
+ * they must be freed after a synchronize_sched().
+ */
+ preempt_disable_notrace();
+ trace_recursion_set(TRACE_CONTROL_BIT);
+ op = rcu_dereference_raw(ftrace_control_list);
+ while (op != &ftrace_list_end) {
+ if (!control_ops_is_disabled(op) &&
+ ftrace_ops_test(op, ip))
+ op->func(ip, parent_ip);
+
+ op = rcu_dereference_raw(op->next);
+ };
+ trace_recursion_clear(TRACE_CONTROL_BIT);
+ preempt_enable_notrace();
+}
+
+static struct ftrace_ops control_ops = {
+ .func = ftrace_ops_control_func,
+};
+
+static void
ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip)
{
struct ftrace_ops *op;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 2c26574..41c54e3 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -288,6 +288,8 @@ struct tracer {
/* for function tracing recursion */
#define TRACE_INTERNAL_BIT (1<<11)
#define TRACE_GLOBAL_BIT (1<<12)
+#define TRACE_CONTROL_BIT (1<<13)
+
/*
* Abuse of the trace_recursion.
* As we need a way to maintain state if we are tracing the function
--
1.7.1


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