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ftrace: Remove use of control list and ops
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Currently perf has its own list function within the ftrace infrastructure
that seems to be used only to allow for it to have per-cpu disabling as well
as a check to make sure that it's not called while RCU is not watching. It
uses something called the "control_ops" which is used to iterate over ops
under it with the control_list_func().

The problem is that this control_ops and control_list_func unnecessarily
complicates the code. By replacing FTRACE_OPS_FL_CONTROL with two new flags
(FTRACE_OPS_FL_RCU and FTRACE_OPS_FL_PER_CPU) we can remove all the code
that is special with the control ops and add the needed checks within the
generic ftrace_list_func().

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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Steven Rostedt (Red Hat) committed Dec 23, 2015
1 parent 030f4e1 commit ba27f2b
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Showing 4 changed files with 57 additions and 108 deletions.
35 changes: 18 additions & 17 deletions include/linux/ftrace.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -76,8 +76,8 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
* ENABLED - set/unset when ftrace_ops is registered/unregistered
* 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:
* PER_CPU - set manualy by ftrace_ops user to denote the ftrace_ops
* could be controlled by following calls:
* ftrace_function_local_enable
* ftrace_function_local_disable
* SAVE_REGS - The ftrace_ops wants regs saved at each function called
Expand Down Expand Up @@ -121,7 +121,7 @@ ftrace_func_t ftrace_ops_get_func(struct ftrace_ops *ops);
enum {
FTRACE_OPS_FL_ENABLED = 1 << 0,
FTRACE_OPS_FL_DYNAMIC = 1 << 1,
FTRACE_OPS_FL_CONTROL = 1 << 2,
FTRACE_OPS_FL_PER_CPU = 1 << 2,
FTRACE_OPS_FL_SAVE_REGS = 1 << 3,
FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED = 1 << 4,
FTRACE_OPS_FL_RECURSION_SAFE = 1 << 5,
Expand All @@ -134,6 +134,7 @@ enum {
FTRACE_OPS_FL_ALLOC_TRAMP = 1 << 12,
FTRACE_OPS_FL_IPMODIFY = 1 << 13,
FTRACE_OPS_FL_PID = 1 << 14,
FTRACE_OPS_FL_RCU = 1 << 15,
};

#ifdef CONFIG_DYNAMIC_FTRACE
Expand All @@ -146,11 +147,11 @@ struct ftrace_ops_hash {
#endif

/*
* Note, ftrace_ops can be referenced outside of RCU protection.
* (Although, for perf, the control ops prevent that). If ftrace_ops is
* allocated and not part of kernel core data, the unregistering of it will
* perform a scheduling on all CPUs to make sure that there are no more users.
* Depending on the load of the system that may take a bit of time.
* Note, ftrace_ops can be referenced outside of RCU protection, unless
* the RCU flag is set. If ftrace_ops is allocated and not part of kernel
* core data, the unregistering of it will perform a scheduling on all CPUs
* to make sure that there are no more users. Depending on the load of the
* system that may take a bit of time.
*
* Any private data added must also take care not to be freed and if private
* data is added to a ftrace_ops that is in core code, the user of the
Expand Down Expand Up @@ -196,34 +197,34 @@ int unregister_ftrace_function(struct ftrace_ops *ops);
void clear_ftrace_function(void);

/**
* ftrace_function_local_enable - enable controlled ftrace_ops on current cpu
* ftrace_function_local_enable - enable 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. If called without preemption
* registered with FTRACE_OPS_FL_PER_CPU. If called without preemption
* disabled, this_cpu_ptr will complain when CONFIG_DEBUG_PREEMPT is enabled.
*/
static inline void ftrace_function_local_enable(struct ftrace_ops *ops)
{
if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL)))
if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_PER_CPU)))
return;

(*this_cpu_ptr(ops->disabled))--;
}

/**
* ftrace_function_local_disable - enable controlled ftrace_ops on current cpu
* ftrace_function_local_disable - disable ftrace_ops on current cpu
*
* This function enables tracing on current cpu by decreasing
* This function disables tracing on current cpu by increasing
* the per cpu control variable.
* It must be called with preemption disabled and only on ftrace_ops
* registered with FTRACE_OPS_FL_CONTROL. If called without preemption
* registered with FTRACE_OPS_FL_PER_CPU. If called without preemption
* disabled, this_cpu_ptr will complain when CONFIG_DEBUG_PREEMPT is enabled.
*/
static inline void ftrace_function_local_disable(struct ftrace_ops *ops)
{
if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL)))
if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_PER_CPU)))
return;

(*this_cpu_ptr(ops->disabled))++;
Expand All @@ -235,12 +236,12 @@ static inline void ftrace_function_local_disable(struct ftrace_ops *ops)
*
* 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. If called without preemption
* registered with FTRACE_OPS_FL_PER_CPU. If called without preemption
* disabled, this_cpu_ptr will complain when CONFIG_DEBUG_PREEMPT is enabled.
*/
static inline int ftrace_function_local_disabled(struct ftrace_ops *ops)
{
WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_CONTROL));
WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_PER_CPU));
return *this_cpu_ptr(ops->disabled);
}

Expand Down
126 changes: 38 additions & 88 deletions kernel/trace/ftrace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -62,8 +62,6 @@
#define FTRACE_HASH_DEFAULT_BITS 10
#define FTRACE_HASH_MAX_BITS 12

#define FL_GLOBAL_CONTROL_MASK (FTRACE_OPS_FL_CONTROL)

#ifdef CONFIG_DYNAMIC_FTRACE
#define INIT_OPS_HASH(opsname) \
.func_hash = &opsname.local_hash, \
Expand Down Expand Up @@ -113,11 +111,9 @@ static int ftrace_disabled __read_mostly;

static DEFINE_MUTEX(ftrace_lock);

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 struct ftrace_ops global_ops;
static struct ftrace_ops control_ops;

static void ftrace_ops_recurs_func(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op, struct pt_regs *regs);
Expand Down Expand Up @@ -203,24 +199,27 @@ void clear_ftrace_function(void)
ftrace_trace_function = ftrace_stub;
}

static void control_ops_disable_all(struct ftrace_ops *ops)
static void per_cpu_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)
static int per_cpu_ops_alloc(struct ftrace_ops *ops)
{
int __percpu *disabled;

if (WARN_ON_ONCE(!(ops->flags & FTRACE_OPS_FL_PER_CPU)))
return -EINVAL;

disabled = alloc_percpu(int);
if (!disabled)
return -ENOMEM;

ops->disabled = disabled;
control_ops_disable_all(ops);
per_cpu_ops_disable_all(ops);
return 0;
}

Expand Down Expand Up @@ -256,10 +255,11 @@ static inline void update_function_graph_func(void) { }
static ftrace_func_t ftrace_ops_get_list_func(struct ftrace_ops *ops)
{
/*
* If this is a dynamic ops or we force list func,
* If this is a dynamic, RCU, or per CPU ops, or we force list func,
* then it needs to call the list anyway.
*/
if (ops->flags & FTRACE_OPS_FL_DYNAMIC || FTRACE_FORCE_LIST_FUNC)
if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_PER_CPU |
FTRACE_OPS_FL_RCU) || FTRACE_FORCE_LIST_FUNC)
return ftrace_ops_list_func;

return ftrace_ops_get_func(ops);
Expand Down Expand Up @@ -383,26 +383,6 @@ 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 void ftrace_update_trampoline(struct ftrace_ops *ops);

static int __register_ftrace_function(struct ftrace_ops *ops)
Expand Down Expand Up @@ -430,14 +410,12 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
if (!core_kernel_data((unsigned long)ops))
ops->flags |= FTRACE_OPS_FL_DYNAMIC;

if (ops->flags & FTRACE_OPS_FL_CONTROL) {
if (control_ops_alloc(ops))
if (ops->flags & FTRACE_OPS_FL_PER_CPU) {
if (per_cpu_ops_alloc(ops))
return -ENOMEM;
add_ftrace_list_ops(&ftrace_control_list, &control_ops, ops);
/* The control_ops needs the trampoline update */
ops = &control_ops;
} else
add_ftrace_ops(&ftrace_ops_list, ops);
}

add_ftrace_ops(&ftrace_ops_list, ops);

/* Always save the function, and reset at unregistering */
ops->saved_func = ops->func;
Expand All @@ -460,11 +438,7 @@ static int __unregister_ftrace_function(struct ftrace_ops *ops)
if (WARN_ON(!(ops->flags & FTRACE_OPS_FL_ENABLED)))
return -EBUSY;

if (ops->flags & FTRACE_OPS_FL_CONTROL) {
ret = remove_ftrace_list_ops(&ftrace_control_list,
&control_ops, ops);
} else
ret = remove_ftrace_ops(&ftrace_ops_list, ops);
ret = remove_ftrace_ops(&ftrace_ops_list, ops);

if (ret < 0)
return ret;
Expand Down Expand Up @@ -2630,7 +2604,7 @@ void __weak arch_ftrace_trampoline_free(struct ftrace_ops *ops)
{
}

static void control_ops_free(struct ftrace_ops *ops)
static void per_cpu_ops_free(struct ftrace_ops *ops)
{
free_percpu(ops->disabled);
}
Expand Down Expand Up @@ -2731,13 +2705,13 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)

if (!command || !ftrace_enabled) {
/*
* If these are control ops, they still need their
* If these are per_cpu ops, they still need their
* per_cpu field freed. Since, function tracing is
* not currently active, we can just free them
* without synchronizing all CPUs.
*/
if (ops->flags & FTRACE_OPS_FL_CONTROL)
control_ops_free(ops);
if (ops->flags & FTRACE_OPS_FL_PER_CPU)
per_cpu_ops_free(ops);
return 0;
}

Expand Down Expand Up @@ -2778,7 +2752,7 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
/*
* Dynamic ops may be freed, we must make sure that all
* callers are done before leaving this function.
* The same goes for freeing the per_cpu data of the control
* The same goes for freeing the per_cpu data of the per_cpu
* ops.
*
* Again, normal synchronize_sched() is not good enough.
Expand All @@ -2789,13 +2763,13 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
* infrastructure to do the synchronization, thus we must do it
* ourselves.
*/
if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_CONTROL)) {
if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_PER_CPU)) {
schedule_on_each_cpu(ftrace_sync);

arch_ftrace_trampoline_free(ops);

if (ops->flags & FTRACE_OPS_FL_CONTROL)
control_ops_free(ops);
if (ops->flags & FTRACE_OPS_FL_PER_CPU)
per_cpu_ops_free(ops);
}

return 0;
Expand Down Expand Up @@ -5185,44 +5159,6 @@ void ftrace_reset_array_ops(struct trace_array *tr)
tr->ops->func = ftrace_stub;
}

static void
ftrace_ops_control_func(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *op, struct pt_regs *regs)
{
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);

/*
* Control funcs (perf) uses RCU. Only trace if
* RCU is currently active.
*/
if (!rcu_is_watching())
goto out;

do_for_each_ftrace_op(op, ftrace_control_list) {
if (!(op->flags & FTRACE_OPS_FL_STUB) &&
!ftrace_function_local_disabled(op) &&
ftrace_ops_test(op, ip, regs))
op->func(ip, parent_ip, op, regs);
} while_for_each_ftrace_op(op);
out:
trace_recursion_clear(TRACE_CONTROL_BIT);
preempt_enable_notrace();
}

static struct ftrace_ops control_ops = {
.func = ftrace_ops_control_func,
.flags = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_INITIALIZED,
INIT_OPS_HASH(control_ops)
};

static inline void
__ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *ignored, struct pt_regs *regs)
Expand All @@ -5239,8 +5175,22 @@ __ftrace_ops_list_func(unsigned long ip, unsigned long parent_ip,
* they must be freed after a synchronize_sched().
*/
preempt_disable_notrace();

do_for_each_ftrace_op(op, ftrace_ops_list) {
if (ftrace_ops_test(op, ip, regs)) {
/*
* Check the following for each ops before calling their func:
* if RCU flag is set, then rcu_is_watching() must be true
* if PER_CPU is set, then ftrace_function_local_disable()
* must be false
* Otherwise test if the ip matches the ops filter
*
* If any of the above fails then the op->func() is not executed.
*/
if ((!(op->flags & FTRACE_OPS_FL_RCU) || rcu_is_watching()) &&
(!(op->flags & FTRACE_OPS_FL_PER_CPU) ||
!ftrace_function_local_disabled(op)) &&
ftrace_ops_test(op, ip, regs)) {

if (FTRACE_WARN_ON(!op->func)) {
pr_warn("op=%p %pS\n", op, op);
goto out;
Expand Down
2 changes: 0 additions & 2 deletions kernel/trace/trace.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -467,8 +467,6 @@ enum {
TRACE_INTERNAL_IRQ_BIT,
TRACE_INTERNAL_SIRQ_BIT,

TRACE_CONTROL_BIT,

TRACE_BRANCH_BIT,
/*
* Abuse of the trace_recursion.
Expand Down
2 changes: 1 addition & 1 deletion kernel/trace/trace_event_perf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -334,7 +334,7 @@ static int perf_ftrace_function_register(struct perf_event *event)
{
struct ftrace_ops *ops = &event->ftrace_ops;

ops->flags |= FTRACE_OPS_FL_CONTROL;
ops->flags |= FTRACE_OPS_FL_PER_CPU | FTRACE_OPS_FL_RCU;
ops->func = perf_ftrace_function_call;
return register_ftrace_function(ops);
}
Expand Down

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