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Date: Sun, 14 Dec 2014 14:21:43 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [PATCH 1/2 v2] tracing: Move enabling tracepoints to just after
rcu_init()
On Sun, Dec 14, 2014 at 03:16:10PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.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@...utronix.de>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
>From an RCU perspective:
Reviewed-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
> 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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