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Message-ID: <20120127172012.GE10601@m.brq.redhat.com>
Date: Fri, 27 Jan 2012 18:20:12 +0100
From: Jiri Olsa <jolsa@...hat.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>, 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 2/7] ftrace: Add enable/disable ftrace_ops control
interface
On Fri, Jan 27, 2012 at 06:02:04PM +0100, Frederic Weisbecker wrote:
> On Fri, Jan 27, 2012 at 05:54:16PM +0100, Jiri Olsa wrote:
> > On Fri, Jan 27, 2012 at 05:40:49PM +0100, Frederic Weisbecker wrote:
> > > On Fri, Jan 27, 2012 at 11:37:14AM +0100, Jiri Olsa wrote:
> > > > On Thu, Jan 26, 2012 at 03:37:29AM +0100, Frederic Weisbecker wrote:
> > > > > On Wed, Jan 25, 2012 at 06:13:41PM -0500, Steven Rostedt wrote:
> > > > > > On Fri, 2012-01-20 at 18:02 +0100, Frederic Weisbecker wrote:
> > > > > > >
> > > > > > > > +/**
> > > > > > > > + * 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()))
> > > > > > > > + return;
> > > > > > > > +
> > > > > > > > + disabled = per_cpu_ptr(ops->disabled, cpu);
> > > > > > > > + atomic_dec(disabled);
> > > > > > > > +}
> > > > > > >
> > > > > > > As you're using this for the local CPU exclusively, I suggest you rather
> > > > > > > rename it to "ftrace_function_{dis,en}able_cpu(struct ftrace_ops *ops)"
> > > > > >
> > > > > > I wonder if "ftrace_function_local_{dis,en}able(ops)" would be better?
> > > > > > That would match something like local_irq_disable/enable.
> > > > >
> > > > > Good idea.
> > > > >
> > > > > >
> > > > > > > and use __get_cpu_var() that does the preempt check for you.
> > > >
> > > > I haven't found preempt check this_cpu_ptr path.. not sure I missed it..
> > > > so I'm keeping the implicit preemt check.
> > >
> > > #ifdef CONFIG_DEBUG_PREEMPT
> > > #define my_cpu_offset per_cpu_offset(smp_processor_id())
> > > #else
> > > #define my_cpu_offset __my_cpu_offset
> > > #endif
> > >
> > > #ifdef CONFIG_DEBUG_PREEMPT
> > > #define this_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, my_cpu_offset)
> > > #else
> > > #define this_cpu_ptr(ptr) __this_cpu_ptr(ptr)
> > > #endif
> > >
> > > And smp_processor_id() has a preemption check.
> >
> > yay.. ok :) so this one is triggered only if there's CONFIG_DEBUG_PREEMPT
> > option enabled.. seems to me it'd better to keep the implicit check anyway.
> >
> > jirka
>
>
> This is a debugging option deemed to lower runtime debugging checks in
> production.
>
> Is there a good reason to keep the check on every case?
none I guess, apart from me feeling better.. ;)
attached new version without the preemt_count check int the WARN_ON_ONCE
thanks,
jirka
---
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index f33fb3b..d95df4b 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -31,16 +31,32 @@ 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_enable, ftrace_function_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 +113,52 @@ 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.
+ */
+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.
+ */
+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.
+ */
+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 e2e0597..c8d2af2 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 b93ecba..55c6ea0 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
--
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