ftrace: Add enable/disable ftrace_ops control interface

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 3 inline functions:
  ftrace_function_local_disable/ftrace_function_local_enable
  - enable/disable the ftrace_ops on current cpu
  ftrace_function_local_disabled
  - get disabled ftrace_ops::disabled value for current cpu

Link: http://lkml.kernel.org/r/1329317514-8131-2-git-send-email-jolsa@redhat.com

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

3 files changed, 172 insertions, 7 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index f33fb3b041c6..64a309d2fbd6 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -31,16 +31,33 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 
 typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip);
 
+/*
+ * FTRACE_OPS_FL_* bits denote the state of ftrace_ops struct and are
+ * set in the flags member.
+ *
+ * ENABLED - set/unset when ftrace_ops is registered/unregistered
+ * GLOBAL  - set manualy by ftrace_ops user to denote the ftrace_ops
+ *           is part of the global tracers sharing the same filter
+ *           via set_ftrace_* debugfs files.
+ * DYNAMIC - set when ftrace_ops is registered to denote dynamically
+ *           allocated ftrace_ops which need special care
+ * CONTROL - set manualy by ftrace_ops user to denote the ftrace_ops
+ *           could be controled by following calls:
+ *             ftrace_function_local_enable
+ *             ftrace_function_local_disable
+ */
 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;
+        int __percpu                    *disabled;
 #ifdef CONFIG_DYNAMIC_FTRACE
         struct ftrace_hash              *notrace_hash;
         struct ftrace_hash              *filter_hash;
@@ -97,6 +114,55 @@ int register_ftrace_function(struct ftrace_ops *ops);
 int unregister_ftrace_function(struct ftrace_ops *ops);
 void clear_ftrace_function(void);
 
+/**
+ * ftrace_function_local_enable - enable controlled ftrace_ops on current cpu
+ *
+ * This function enables tracing on current 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. If called without preemption
+ * disabled, this_cpu_ptr will complain when CONFIG_DEBUG_PREEMPT is enabled.
+ */
+static inline void ftrace_function_local_enable(struct ftrace_ops *ops)
+{
+        if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL)))
+                return;
+
+        (*this_cpu_ptr(ops->disabled))--;
+}
+
+/**
+ * ftrace_function_local_disable - enable controlled ftrace_ops on current cpu
+ *
+ * This function enables tracing on current 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. If called without preemption
+ * disabled, this_cpu_ptr will complain when CONFIG_DEBUG_PREEMPT is enabled.
+ */
+static inline void ftrace_function_local_disable(struct ftrace_ops *ops)
+{
+        if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL)))
+                return;
+
+        (*this_cpu_ptr(ops->disabled))++;
+}
+
+/**
+ * ftrace_function_local_disabled - returns ftrace_ops disabled value
+ *                                  on current cpu
+ *
+ * This function returns value of ftrace_ops::disabled on current cpu.
+ * It must be called with preemption disabled and only on ftrace_ops
+ * registered with FTRACE_OPS_FL_CONTROL. If called without preemption
+ * disabled, this_cpu_ptr will complain when CONFIG_DEBUG_PREEMPT is enabled.
+ */
+static inline int ftrace_function_local_disabled(struct ftrace_ops *ops)
+{
+        WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL));
+        return *this_cpu_ptr(ops->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 d1499e910fe8..f615f974d90e 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -62,6 +62,8 @@
 #define FTRACE_HASH_DEFAULT_BITS 10
 #define FTRACE_HASH_MAX_BITS 12
 
+#define FL_GLOBAL_CONTROL_MASK (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;
@@ -89,12 +91,14 @@ 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);
@@ -168,6 +172,32 @@ 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)
+                *per_cpu_ptr(ops->disabled, cpu) = 1;
+}
+
+static int control_ops_alloc(struct ftrace_ops *ops)
+{
+        int __percpu *disabled;
+
+        disabled = alloc_percpu(int);
+        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 void update_global_ops(void)
 {
         ftrace_func_t func;
@@ -259,6 +289,26 @@ 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)
@@ -270,15 +320,20 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
         if (WARN_ON(ops->flags & FTRACE_OPS_FL_ENABLED))
                 return -EBUSY;
 
+        /* We don't support both control and global flags set. */
+        if ((ops->flags & FL_GLOBAL_CONTROL_MASK) == FL_GLOBAL_CONTROL_MASK)
+                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);
 
@@ -302,11 +357,23 @@ 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);
 
@@ -3874,6 +3941,36 @@ 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 (!ftrace_function_local_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 b93ecbadad6d..55c6ea00f28a 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