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Date: Wed, 21 Dec 2011 11:01:33 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Jiri Olsa <jolsa@...hat.com>
Cc: fweisbec@...il.com, mingo@...hat.com, paulus@...ba.org,
acme@...stprotocols.net, a.p.zijlstra@...llo.nl,
linux-kernel@...r.kernel.org, aarapov@...hat.com
Subject: Re: [PATCH 3/8] ftrace: Add enable/disable ftrace_ops control
interface
On Wed, 2011-12-21 at 12:48 +0100, Jiri Olsa wrote:
> 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@...hat.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())
The WARN_ON_ONCE() should also include the !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())
Same here.
> + 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);
Again, the use of "this_cpu_ptr" is wrong. Gah! We should nuke all of
that crap.
> + 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)
No biggy, but I usually find:
if (ops->flags & FL_GLOBAL_CONTROL)
more readable. With what you have, I looked at that condition three
times to figure out what was different between what was '&'d with the
flags and what was being equal too. Usually the ((flags & X) == Y) is
done to check if a subset of bits are set within a mask of bits.
> + 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);
Much better and easier to read :)
> 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);
>
The rest looks good.
-- Steve
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