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Subject[PATCH 1/2 v2] tracing: Move enabling tracepoints to just after rcu_init()
From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

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

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
include/linux/ftrace.h | 6 ++++++
init/main.c | 4 ++++
kernel/trace/trace.c | 8 +++++++-
kernel/trace/trace.h | 13 +++++++++++++
kernel/trace/trace_events.c | 10 ++++++++--
kernel/trace/trace_syscalls.c | 7 ++-----
6 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ed501953f0b2..f4bc14b7d444 100644
--- 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 800a0daede7e..70687069f8e2 100644
--- 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 4ceb2546c7ef..ec3ca694665f 100644
--- 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 3255dfb054a0..c138c149d6ef 100644
--- 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 f9d0cbe014b7..fd9deb0e03f0 100644
--- 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 a72f3d8d813e..ec239771c175 100644
--- 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

--
2.1.3



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