tracing: Move enabling tracepoints to just after rcu_init()

Enabling tracepoints at boot up can be very useful. The tracepoint
can be initialized right after RCU has been. There's no need to
wait for the early_initcall() to be called. That's too late for some
things that can use tracepoints for debugging. Move the logic to
enable tracepoints out of the initcalls and into init/main.c to
right after rcu_init().

This also allows trace_printk() to be used early too.

Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1412121539300.16494@nanos
Link: http://lkml.kernel.org/r/20141214164104.307127356@goodmis.org
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ed50195..f4bc14b 100644 (file)
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -39,6 +39,12 @@
 # define FTRACE_FORCE_LIST_FUNC 0
 #endif
 
+/* Main tracing buffer and events set up */
+#ifdef CONFIG_TRACING
+void trace_init(void);
+#else
+static inline void trace_init(void) { }
+#endif
 
 struct module;
 struct ftrace_hash;

diff --git a/init/main.c b/init/main.c
index 800a0da..7068706 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -577,6 +577,10 @@ asmlinkage __visible void __init start_kernel(void)
                local_irq_disable();
        idr_init_cache();
        rcu_init();
+
+       /* trace_printk() and trace points may be used after this */
+       trace_init();
+
        context_tracking_init();
        radix_tree_init();
        /* init some links before init_ISA_irqs() */

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4ceb254..ec3ca69 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6876,6 +6876,13 @@ out:
        return ret;
 }
 
+void __init trace_init(void)
+{
+       tracer_alloc_buffers();
+       init_ftrace_syscalls();
+       trace_event_init();     
+}
+
 __init static int clear_boot_tracer(void)
 {
        /*
@@ -6895,6 +6902,5 @@ __init static int clear_boot_tracer(void)
        return 0;
 }
 
-early_initcall(tracer_alloc_buffers);
 fs_initcall(tracer_init_debugfs);
 late_initcall(clear_boot_tracer);

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 3255dfb..c138c14 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1301,4 +1301,17 @@ int perf_ftrace_event_register(struct ftrace_event_call *call,
 #define perf_ftrace_event_register NULL
 #endif
 
+#ifdef CONFIG_FTRACE_SYSCALLS
+void init_ftrace_syscalls(void);
+#else
+static inline void init_ftrace_syscalls(void) { }
+#endif
+
+#ifdef CONFIG_EVENT_TRACING
+void trace_event_init(void);
+#else
+static inline void __init trace_event_init(void) { }
+#endif
+
+
 #endif /* _LINUX_KERNEL_TRACE_H */

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index f9d0cbe..fd9deb0 100644 (file)
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -2477,8 +2477,14 @@ static __init int event_trace_init(void)
 #endif
        return 0;
 }
-early_initcall(event_trace_memsetup);
-core_initcall(event_trace_enable);
+
+void __init trace_event_init(void)
+{
+       event_trace_memsetup();
+       init_ftrace_syscalls();
+       event_trace_enable();
+}
+
 fs_initcall(event_trace_init);
 
 #ifdef CONFIG_FTRACE_STARTUP_TEST

diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
index a72f3d8..ec23977 100644 (file)
--- a/kernel/trace/trace_syscalls.c
+++ b/kernel/trace/trace_syscalls.c
@@ -514,7 +514,7 @@ unsigned long __init __weak arch_syscall_addr(int nr)
        return (unsigned long)sys_call_table[nr];
 }
 
-static int __init init_ftrace_syscalls(void)
+void __init init_ftrace_syscalls(void)
 {
        struct syscall_metadata *meta;
        unsigned long addr;
@@ -524,7 +524,7 @@ static int __init init_ftrace_syscalls(void)
                                    GFP_KERNEL);
        if (!syscalls_metadata) {
                WARN_ON(1);
-               return -ENOMEM;
+               return;
        }
 
        for (i = 0; i < NR_syscalls; i++) {
@@ -536,10 +536,7 @@ static int __init init_ftrace_syscalls(void)
                meta->syscall_nr = i;
                syscalls_metadata[i] = meta;
        }
-
-       return 0;
 }
-early_initcall(init_ftrace_syscalls);
 
 #ifdef CONFIG_PERF_EVENTS