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Commit e7d3737e authored by Frederic Weisbecker's avatar Frederic Weisbecker Committed by Ingo Molnar
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tracing/function-return-tracer: support for dynamic ftrace on function return tracer 



This patch adds the support for dynamic tracing on the function return tracer.
The whole difference with normal dynamic function tracing is that we don't need
to hook on a particular callback. The only pro that we want is to nop or set
dynamically the calls to ftrace_caller (which is ftrace_return_caller here).

Some security checks ensure that we are not trying to launch dynamic tracing for
return tracing while normal function tracing is already running.

An example of trace with getnstimeofday set as a filter:

ktime_get_ts+0x22/0x50 -> getnstimeofday (2283 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1396 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1825 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1426 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1524 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1382 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1434 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1464 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1502 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1404 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1397 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1051 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1314 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1344 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1163 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1390 ns)
ktime_get_ts+0x22/0x50 -> getnstimeofday (1374 ns)

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent b01c7466

arch/x86/kernel/entry_32.S

+11 −7
Original line number Diff line number Diff line
@@ -1190,7 +1190,7 @@ ENTRY(mcount) 
	jnz trace

#ifdef CONFIG_FUNCTION_RET_TRACER

	cmpl $ftrace_stub, ftrace_function_return

	jnz trace_return

	jnz ftrace_return_caller

#endif

.globl ftrace_stub

ftrace_stub:
@@ -1211,9 +1211,15 @@ trace: 
	popl %ecx

	popl %eax

	jmp ftrace_stub

END(mcount)

#endif /* CONFIG_DYNAMIC_FTRACE */

#endif /* CONFIG_FUNCTION_TRACER */



#ifdef CONFIG_FUNCTION_RET_TRACER

trace_return:

ENTRY(ftrace_return_caller)

	cmpl $0, function_trace_stop

	jne ftrace_stub



	pushl %eax

	pushl %ecx

	pushl %edx
@@ -1223,7 +1229,8 @@ trace_return: 
	popl %edx

	popl %ecx

	popl %eax

	jmp ftrace_stub

	ret

END(ftrace_return_caller)



.globl return_to_handler

return_to_handler:
@@ -1237,10 +1244,7 @@ return_to_handler: 
	popl %ecx

	popl %eax

	ret

#endif /* CONFIG_FUNCTION_RET_TRACER */

END(mcount)

#endif /* CONFIG_DYNAMIC_FTRACE */

#endif /* CONFIG_FUNCTION_TRACER */

#endif



.section .rodata,"a"

#include "syscall_table_32.S"

arch/x86/kernel/ftrace.c

+130 −128
Original line number Diff line number Diff line
@@ -24,134 +24,6 @@ 
#include <asm/nmi.h>







#ifdef CONFIG_FUNCTION_RET_TRACER



/*

 * These functions are picked from those used on

 * this page for dynamic ftrace. They have been

 * simplified to ignore all traces in NMI context.

 */

static atomic_t in_nmi;



void ftrace_nmi_enter(void)

{

	atomic_inc(&in_nmi);

}



void ftrace_nmi_exit(void)

{

	atomic_dec(&in_nmi);

}



/* Add a function return address to the trace stack on thread info.*/

static int push_return_trace(unsigned long ret, unsigned long long time,

				unsigned long func)

{

	int index;

	struct thread_info *ti = current_thread_info();



	/* The return trace stack is full */

	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1)

		return -EBUSY;



	index = ++ti->curr_ret_stack;

	barrier();

	ti->ret_stack[index].ret = ret;

	ti->ret_stack[index].func = func;

	ti->ret_stack[index].calltime = time;



	return 0;

}



/* Retrieve a function return address to the trace stack on thread info.*/

static void pop_return_trace(unsigned long *ret, unsigned long long *time,

				unsigned long *func)

{

	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;

	ti->curr_ret_stack--;

}



/*

 * Send the trace to the ring-buffer.

 * @return the original return address.

 */

unsigned long ftrace_return_to_handler(void)

{

	struct ftrace_retfunc trace;

	pop_return_trace(&trace.ret, &trace.calltime, &trace.func);

	trace.rettime = cpu_clock(raw_smp_processor_id());

	ftrace_function_return(&trace);



	return trace.ret;

}



/*

 * Hook the return address and push it in the stack of return addrs

 * in current thread info.

 */

void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)

{

	unsigned long old;

	unsigned long long calltime;

	int faulted;

	unsigned long return_hooker = (unsigned long)

				&return_to_handler;



	/* Nmi's are currently unsupported */

	if (atomic_read(&in_nmi))

		return;



	/*

	 * Protect against fault, even if it shouldn't

	 * happen. This tool is too much intrusive to

	 * ignore such a protection.

	 */

	asm volatile(

		"1: movl (%[parent_old]), %[old]\n"

		"2: movl %[return_hooker], (%[parent_replaced])\n"

		"   movl $0, %[faulted]\n"



		".section .fixup, \"ax\"\n"

		"3: movl $1, %[faulted]\n"

		".previous\n"



		".section __ex_table, \"a\"\n"

		"   .long 1b, 3b\n"

		"   .long 2b, 3b\n"

		".previous\n"



		: [parent_replaced] "=r" (parent), [old] "=r" (old),

		  [faulted] "=r" (faulted)

		: [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)

		: "memory"

	);



	if (WARN_ON(faulted)) {

		unregister_ftrace_return();

		return;

	}



	if (WARN_ON(!__kernel_text_address(old))) {

		unregister_ftrace_return();

		*parent = old;

		return;

	}



	calltime = cpu_clock(raw_smp_processor_id());



	if (push_return_trace(old, calltime, self_addr) == -EBUSY)

		*parent = old;

}



#endif



#ifdef CONFIG_DYNAMIC_FTRACE



union ftrace_code_union {
@@ -450,3 +322,133 @@ int __init ftrace_dyn_arch_init(void *data) 
	return 0;

}

#endif



#ifdef CONFIG_FUNCTION_RET_TRACER



#ifndef CONFIG_DYNAMIC_FTRACE



/*

 * These functions are picked from those used on

 * this page for dynamic ftrace. They have been

 * simplified to ignore all traces in NMI context.

 */

static atomic_t in_nmi;



void ftrace_nmi_enter(void)

{

	atomic_inc(&in_nmi);

}



void ftrace_nmi_exit(void)

{

	atomic_dec(&in_nmi);

}

#endif /* !CONFIG_DYNAMIC_FTRACE */



/* Add a function return address to the trace stack on thread info.*/

static int push_return_trace(unsigned long ret, unsigned long long time,

				unsigned long func)

{

	int index;

	struct thread_info *ti = current_thread_info();



	/* The return trace stack is full */

	if (ti->curr_ret_stack == FTRACE_RET_STACK_SIZE - 1)

		return -EBUSY;



	index = ++ti->curr_ret_stack;

	barrier();

	ti->ret_stack[index].ret = ret;

	ti->ret_stack[index].func = func;

	ti->ret_stack[index].calltime = time;



	return 0;

}



/* Retrieve a function return address to the trace stack on thread info.*/

static void pop_return_trace(unsigned long *ret, unsigned long long *time,

				unsigned long *func)

{

	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;

	ti->curr_ret_stack--;

}



/*

 * Send the trace to the ring-buffer.

 * @return the original return address.

 */

unsigned long ftrace_return_to_handler(void)

{

	struct ftrace_retfunc trace;

	pop_return_trace(&trace.ret, &trace.calltime, &trace.func);

	trace.rettime = cpu_clock(raw_smp_processor_id());

	ftrace_function_return(&trace);



	return trace.ret;

}



/*

 * Hook the return address and push it in the stack of return addrs

 * in current thread info.

 */

void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)

{

	unsigned long old;

	unsigned long long calltime;

	int faulted;

	unsigned long return_hooker = (unsigned long)

				&return_to_handler;



	/* Nmi's are currently unsupported */

	if (atomic_read(&in_nmi))

		return;



	/*

	 * Protect against fault, even if it shouldn't

	 * happen. This tool is too much intrusive to

	 * ignore such a protection.

	 */

	asm volatile(

		"1: movl (%[parent_old]), %[old]\n"

		"2: movl %[return_hooker], (%[parent_replaced])\n"

		"   movl $0, %[faulted]\n"



		".section .fixup, \"ax\"\n"

		"3: movl $1, %[faulted]\n"

		".previous\n"



		".section __ex_table, \"a\"\n"

		"   .long 1b, 3b\n"

		"   .long 2b, 3b\n"

		".previous\n"



		: [parent_replaced] "=r" (parent), [old] "=r" (old),

		  [faulted] "=r" (faulted)

		: [parent_old] "0" (parent), [return_hooker] "r" (return_hooker)

		: "memory"

	);



	if (WARN_ON(faulted)) {

		unregister_ftrace_return();

		return;

	}



	if (WARN_ON(!__kernel_text_address(old))) {

		unregister_ftrace_return();

		*parent = old;

		return;

	}



	calltime = cpu_clock(raw_smp_processor_id());



	if (push_return_trace(old, calltime, self_addr) == -EBUSY)

		*parent = old;

}



#endif /* CONFIG_FUNCTION_RET_TRACER */

include/linux/ftrace.h

+15 −1
Original line number Diff line number Diff line
@@ -25,6 +25,17 @@ struct ftrace_ops { 


extern int function_trace_stop;



/*

 * Type of the current tracing.

 */

enum ftrace_tracing_type_t {

	FTRACE_TYPE_ENTER = 0, /* Hook the call of the function */

	FTRACE_TYPE_RETURN,	/* Hook the return of the function */

};



/* Current tracing type, default is FTRACE_TYPE_ENTER */

extern enum ftrace_tracing_type_t ftrace_tracing_type;



/**

 * ftrace_stop - stop function tracer.

 *
@@ -104,6 +115,9 @@ extern int ftrace_update_ftrace_func(ftrace_func_t func); 
extern void ftrace_caller(void);

extern void ftrace_call(void);

extern void mcount_call(void);

#ifdef CONFIG_FUNCTION_RET_TRACER

extern void ftrace_return_caller(void);

#endif



/**

 * ftrace_make_nop - convert code into top
@@ -310,7 +324,7 @@ struct ftrace_retfunc { 
/* Type of a callback handler of tracing return function */

typedef void (*trace_function_return_t)(struct ftrace_retfunc *);



extern void register_ftrace_return(trace_function_return_t func);

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);

kernel/trace/Kconfig

+0 −1
Original line number Diff line number Diff line
@@ -59,7 +59,6 @@ config FUNCTION_TRACER 


config FUNCTION_RET_TRACER

	bool "Kernel Function return Tracer"

	depends on !DYNAMIC_FTRACE

	depends on HAVE_FUNCTION_RET_TRACER

	depends on FUNCTION_TRACER

	help

kernel/trace/ftrace.c

+53 −5
Original line number Diff line number Diff line
@@ -50,6 +50,9 @@ static int last_ftrace_enabled; 
/* Quick disabling of function tracer. */

int function_trace_stop;



/* By default, current tracing type is normal tracing. */

enum ftrace_tracing_type_t ftrace_tracing_type = FTRACE_TYPE_ENTER;



/*

 * ftrace_disabled is set when an anomaly is discovered.

 * ftrace_disabled is much stronger than ftrace_enabled.
@@ -385,12 +388,21 @@ static void ftrace_bug(int failed, unsigned long ip) 
	}

}



#define FTRACE_ADDR ((long)(ftrace_caller))



static int

__ftrace_replace_code(struct dyn_ftrace *rec, int enable)

{

	unsigned long ip, fl;

	unsigned long ftrace_addr;



#ifdef CONFIG_FUNCTION_RET_TRACER

	if (ftrace_tracing_type == FTRACE_TYPE_ENTER)

		ftrace_addr = (unsigned long)ftrace_caller;

	else

		ftrace_addr = (unsigned long)ftrace_return_caller;

#else

	ftrace_addr = (unsigned long)ftrace_caller;

#endif



	ip = rec->ip;
@@ -450,9 +462,9 @@ __ftrace_replace_code(struct dyn_ftrace *rec, int enable) 
	}



	if (rec->flags & FTRACE_FL_ENABLED)

		return ftrace_make_call(rec, FTRACE_ADDR);

		return ftrace_make_call(rec, ftrace_addr);

	else

		return ftrace_make_nop(NULL, rec, FTRACE_ADDR);

		return ftrace_make_nop(NULL, rec, ftrace_addr);

}



static void ftrace_replace_code(int enable)
@@ -1405,10 +1417,17 @@ int register_ftrace_function(struct ftrace_ops *ops) 
		return -1;



	mutex_lock(&ftrace_sysctl_lock);



	if (ftrace_tracing_type == FTRACE_TYPE_RETURN) {

		ret = -EBUSY;

		goto out;

	}



	ret = __register_ftrace_function(ops);

	ftrace_startup();

	mutex_unlock(&ftrace_sysctl_lock);



out:

	mutex_unlock(&ftrace_sysctl_lock);

	return ret;

}
@@ -1474,16 +1493,45 @@ ftrace_enable_sysctl(struct ctl_table *table, int write, 
}



#ifdef CONFIG_FUNCTION_RET_TRACER



/* The callback that hooks the return of a function */

trace_function_return_t ftrace_function_return =

			(trace_function_return_t)ftrace_stub;

void register_ftrace_return(trace_function_return_t func)



int register_ftrace_return(trace_function_return_t func)

{

	int ret = 0;



	mutex_lock(&ftrace_sysctl_lock);



	/*

	 * Don't launch return tracing if normal function

	 * tracing is already running.

	 */

	if (ftrace_trace_function != ftrace_stub) {

		ret = -EBUSY;

		goto out;

	}



	ftrace_tracing_type = FTRACE_TYPE_RETURN;

	ftrace_function_return = func;

	ftrace_startup();



out:

	mutex_unlock(&ftrace_sysctl_lock);

	return ret;

}



void unregister_ftrace_return(void)

{

	mutex_lock(&ftrace_sysctl_lock);



	ftrace_function_return = (trace_function_return_t)ftrace_stub;

	ftrace_shutdown();

	/* Restore normal tracing type */

	ftrace_tracing_type = FTRACE_TYPE_ENTER;



	mutex_unlock(&ftrace_sysctl_lock);

}

#endif