Commit f201ae23 authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Ingo Molnar
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tracing/function-return-tracer: store return stack into task_struct and allocate it dynamically



Impact: use deeper function tracing depth safely

Some tests showed that function return tracing needed a more deeper depth
of function calls. But it could be unsafe to store these return addresses
to the stack.

So these arrays will now be allocated dynamically into task_struct of current
only when the tracer is activated.

Typical scheme when tracer is activated:
- allocate a return stack for each task in global list.
- fork: allocate the return stack for the newly created task
- exit: free return stack of current
- idle init: same as fork

I chose a default depth of 50. I don't have overruns anymore.
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent a0a70c73
......@@ -29,7 +29,6 @@ struct dyn_arch_ftrace {
#endif /* CONFIG_FUNCTION_TRACER */
#ifdef CONFIG_FUNCTION_RET_TRACER
#define FTRACE_RET_STACK_SIZE 20
#ifndef __ASSEMBLY__
......
......@@ -40,36 +40,8 @@ struct thread_info {
*/
__u8 supervisor_stack[0];
#endif
#ifdef CONFIG_FUNCTION_RET_TRACER
/* Index of current stored adress in ret_stack */
int curr_ret_stack;
/* Stack of return addresses for return function tracing */
struct ftrace_ret_stack ret_stack[FTRACE_RET_STACK_SIZE];
/*
* Number of functions that haven't been traced
* because of depth overrun.
*/
atomic_t trace_overrun;
#endif
};
#ifdef CONFIG_FUNCTION_RET_TRACER
#define INIT_THREAD_INFO(tsk) \
{ \
.task = &tsk, \
.exec_domain = &default_exec_domain, \
.flags = 0, \
.cpu = 0, \
.preempt_count = 1, \
.addr_limit = KERNEL_DS, \
.restart_block = { \
.fn = do_no_restart_syscall, \
}, \
.curr_ret_stack = -1,\
.trace_overrun = ATOMIC_INIT(0) \
}
#else
#define INIT_THREAD_INFO(tsk) \
{ \
.task = &tsk, \
......@@ -82,7 +54,6 @@ struct thread_info {
.fn = do_no_restart_syscall, \
}, \
}
#endif
#define init_thread_info (init_thread_union.thread_info)
#define init_stack (init_thread_union.stack)
......
......@@ -350,19 +350,21 @@ static int push_return_trace(unsigned long ret, unsigned long long time,
unsigned long func)
{
int index;
struct thread_info *ti = current_thread_info();
if (!current->ret_stack)
return -EBUSY;
/* The return trace stack is full */
if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1) {
atomic_inc(&ti->trace_overrun);
if (current->curr_ret_stack == FTRACE_RETFUNC_DEPTH - 1) {
atomic_inc(&current->trace_overrun);
return -EBUSY;
}
index = ++ti->curr_ret_stack;
index = ++current->curr_ret_stack;
barrier();
ti->ret_stack[index].ret = ret;
ti->ret_stack[index].func = func;
ti->ret_stack[index].calltime = time;
current->ret_stack[index].ret = ret;
current->ret_stack[index].func = func;
current->ret_stack[index].calltime = time;
return 0;
}
......@@ -373,13 +375,12 @@ static void pop_return_trace(unsigned long *ret, unsigned long long *time,
{
int index;
struct thread_info *ti = current_thread_info();
index = ti->curr_ret_stack;
*ret = ti->ret_stack[index].ret;
*func = ti->ret_stack[index].func;
*time = ti->ret_stack[index].calltime;
*overrun = atomic_read(&ti->trace_overrun);
ti->curr_ret_stack--;
index = current->curr_ret_stack;
*ret = current->ret_stack[index].ret;
*func = current->ret_stack[index].func;
*time = current->ret_stack[index].calltime;
*overrun = atomic_read(&current->trace_overrun);
current->curr_ret_stack--;
}
/*
......
......@@ -323,6 +323,8 @@ struct ftrace_retfunc {
};
#ifdef CONFIG_FUNCTION_RET_TRACER
#define FTRACE_RETFUNC_DEPTH 50
#define FTRACE_RETSTACK_ALLOC_SIZE 32
/* Type of a callback handler of tracing return function */
typedef void (*trace_function_return_t)(struct ftrace_retfunc *);
......@@ -330,6 +332,9 @@ extern int register_ftrace_return(trace_function_return_t func);
/* The current handler in use */
extern trace_function_return_t ftrace_function_return;
extern void unregister_ftrace_return(void);
extern void ftrace_retfunc_init_task(struct task_struct *t);
extern void ftrace_retfunc_exit_task(struct task_struct *t);
#endif
#endif /* _LINUX_FTRACE_H */
......@@ -1352,6 +1352,17 @@ struct task_struct {
unsigned long default_timer_slack_ns;
struct list_head *scm_work_list;
#ifdef CONFIG_FUNCTION_RET_TRACER
/* Index of current stored adress in ret_stack */
int curr_ret_stack;
/* Stack of return addresses for return function tracing */
struct ftrace_ret_stack *ret_stack;
/*
* Number of functions that haven't been traced
* because of depth overrun.
*/
atomic_t trace_overrun;
#endif
};
/*
......@@ -2006,18 +2017,6 @@ static inline void setup_thread_stack(struct task_struct *p, struct task_struct
{
*task_thread_info(p) = *task_thread_info(org);
task_thread_info(p)->task = p;
#ifdef CONFIG_FUNCTION_RET_TRACER
/*
* When fork() creates a child process, this function is called.
* But the child task may not inherit the return adresses traced
* by the return function tracer because it will directly execute
* in userspace and will not return to kernel functions its parent
* used.
*/
task_thread_info(p)->curr_ret_stack = -1;
atomic_set(&task_thread_info(p)->trace_overrun, 0);
#endif
}
static inline unsigned long *end_of_stack(struct task_struct *p)
......
......@@ -47,6 +47,7 @@
#include <linux/task_io_accounting_ops.h>
#include <linux/tracehook.h>
#include <trace/sched.h>
#include <linux/ftrace.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
......@@ -1127,7 +1128,9 @@ NORET_TYPE void do_exit(long code)
preempt_disable();
/* causes final put_task_struct in finish_task_switch(). */
tsk->state = TASK_DEAD;
#ifdef CONFIG_FUNCTION_RET_TRACER
ftrace_retfunc_exit_task(tsk);
#endif
schedule();
BUG();
/* Avoid "noreturn function does return". */
......
......@@ -47,6 +47,7 @@
#include <linux/mount.h>
#include <linux/audit.h>
#include <linux/memcontrol.h>
#include <linux/ftrace.h>
#include <linux/profile.h>
#include <linux/rmap.h>
#include <linux/acct.h>
......@@ -1269,6 +1270,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
total_forks++;
spin_unlock(&current->sighand->siglock);
write_unlock_irq(&tasklist_lock);
#ifdef CONFIG_FUNCTION_RET_TRACER
ftrace_retfunc_init_task(p);
#endif
proc_fork_connector(p);
cgroup_post_fork(p);
return p;
......
......@@ -5901,6 +5901,9 @@ void __cpuinit init_idle(struct task_struct *idle, int cpu)
* The idle tasks have their own, simple scheduling class:
*/
idle->sched_class = &idle_sched_class;
#ifdef CONFIG_FUNCTION_RET_TRACER
ftrace_retfunc_init_task(idle);
#endif
}
/*
......
......@@ -1498,10 +1498,77 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
#ifdef CONFIG_FUNCTION_RET_TRACER
static atomic_t ftrace_retfunc_active;
/* The callback that hooks the return of a function */
trace_function_return_t ftrace_function_return =
(trace_function_return_t)ftrace_stub;
/* Try to assign a return stack array on FTRACE_RETSTACK_ALLOC_SIZE tasks. */
static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
{
int i;
int ret = 0;
unsigned long flags;
int start = 0, end = FTRACE_RETSTACK_ALLOC_SIZE;
struct task_struct *g, *t;
for (i = 0; i < FTRACE_RETSTACK_ALLOC_SIZE; i++) {
ret_stack_list[i] = kmalloc(FTRACE_RETFUNC_DEPTH
* sizeof(struct ftrace_ret_stack),
GFP_KERNEL);
if (!ret_stack_list[i]) {
start = 0;
end = i;
ret = -ENOMEM;
goto free;
}
}
read_lock_irqsave(&tasklist_lock, flags);
do_each_thread(g, t) {
if (start == end) {
ret = -EAGAIN;
goto unlock;
}
if (t->ret_stack == NULL) {
t->ret_stack = ret_stack_list[start++];
t->curr_ret_stack = -1;
atomic_set(&t->trace_overrun, 0);
}
} while_each_thread(g, t);
unlock:
read_unlock_irqrestore(&tasklist_lock, flags);
free:
for (i = start; i < end; i++)
kfree(ret_stack_list[i]);
return ret;
}
/* Allocate a return stack for each task */
static int start_return_tracing(void)
{
struct ftrace_ret_stack **ret_stack_list;
int ret;
ret_stack_list = kmalloc(FTRACE_RETSTACK_ALLOC_SIZE *
sizeof(struct ftrace_ret_stack *),
GFP_KERNEL);
if (!ret_stack_list)
return -ENOMEM;
do {
ret = alloc_retstack_tasklist(ret_stack_list);
} while (ret == -EAGAIN);
kfree(ret_stack_list);
return ret;
}
int register_ftrace_return(trace_function_return_t func)
{
int ret = 0;
......@@ -1516,7 +1583,12 @@ int register_ftrace_return(trace_function_return_t func)
ret = -EBUSY;
goto out;
}
atomic_inc(&ftrace_retfunc_active);
ret = start_return_tracing();
if (ret) {
atomic_dec(&ftrace_retfunc_active);
goto out;
}
ftrace_tracing_type = FTRACE_TYPE_RETURN;
ftrace_function_return = func;
ftrace_startup();
......@@ -1530,6 +1602,7 @@ void unregister_ftrace_return(void)
{
mutex_lock(&ftrace_sysctl_lock);
atomic_dec(&ftrace_retfunc_active);
ftrace_function_return = (trace_function_return_t)ftrace_stub;
ftrace_shutdown();
/* Restore normal tracing type */
......@@ -1537,6 +1610,27 @@ void unregister_ftrace_return(void)
mutex_unlock(&ftrace_sysctl_lock);
}
/* Allocate a return stack for newly created task */
void ftrace_retfunc_init_task(struct task_struct *t)
{
if (atomic_read(&ftrace_retfunc_active)) {
t->ret_stack = kmalloc(FTRACE_RETFUNC_DEPTH
* sizeof(struct ftrace_ret_stack),
GFP_KERNEL);
if (!t->ret_stack)
return;
t->curr_ret_stack = -1;
atomic_set(&t->trace_overrun, 0);
} else
t->ret_stack = NULL;
}
void ftrace_retfunc_exit_task(struct task_struct *t)
{
kfree(t->ret_stack);
t->ret_stack = NULL;
}
#endif
......
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