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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

arch/x86/include/asm/ftrace.h

+0 −1
Original line number Diff line number Diff line
@@ -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__

arch/x86/include/asm/thread_info.h

+0 −29
Original line number Diff line number Diff line
@@ -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)

arch/x86/kernel/ftrace.c

+15 −14
Original line number Diff line number Diff line
@@ -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--;

}



/*

include/linux/ftrace.h

+5 −0
Original line number Diff line number Diff line
@@ -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 */

include/linux/sched.h

+11 −12
Original line number Diff line number Diff line
@@ -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)