Commit 60a7ecf4 authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar
Browse files

ftrace: add quick function trace stop 



Impact: quick start and stop of function tracer

This patch adds a way to disable the function tracer quickly without
the need to run kstop_machine. It adds a new variable called
function_trace_stop which will stop the calls to functions from mcount
when set.  This is just an on/off switch and does not handle recursion
like preempt_disable().

It's main purpose is to help other tracers/debuggers start and stop tracing
fuctions without the need to call kstop_machine.

The config option HAVE_FUNCTION_TRACE_MCOUNT_TEST is added for archs
that implement the testing of the function_trace_stop in the mcount
arch dependent code. Otherwise, the test is done in the C code.

x86 is the only arch at the moment that supports this.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 79c81d22

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ config X86 
	select HAVE_FTRACE_MCOUNT_RECORD

	select HAVE_DYNAMIC_FTRACE

	select HAVE_FUNCTION_TRACER

	select HAVE_FUNCTION_TRACE_MCOUNT_TEST

	select HAVE_KVM if ((X86_32 && !X86_VOYAGER && !X86_VISWS && !X86_NUMAQ) || X86_64)

	select HAVE_ARCH_KGDB if !X86_VOYAGER

	select HAVE_ARCH_TRACEHOOK

arch/x86/kernel/entry_32.S

+6 −0
Original line number Diff line number Diff line
@@ -1157,6 +1157,9 @@ ENTRY(mcount) 
END(mcount)



ENTRY(ftrace_caller)

	cmpl $0, function_trace_stop

	jne  ftrace_stub



	pushl %eax

	pushl %ecx

	pushl %edx
@@ -1180,6 +1183,9 @@ END(ftrace_caller) 
#else /* ! CONFIG_DYNAMIC_FTRACE */



ENTRY(mcount)

	cmpl $0, function_trace_stop

	jne  ftrace_stub



	cmpl $ftrace_stub, ftrace_trace_function

	jnz trace

.globl ftrace_stub

arch/x86/kernel/entry_64.S

+5 −0
Original line number Diff line number Diff line
@@ -68,6 +68,8 @@ ENTRY(mcount) 
END(mcount)



ENTRY(ftrace_caller)

	cmpl $0, function_trace_stop

	jne  ftrace_stub



	/* taken from glibc */

	subq $0x38, %rsp
@@ -103,6 +105,9 @@ END(ftrace_caller) 


#else /* ! CONFIG_DYNAMIC_FTRACE */

ENTRY(mcount)

	cmpl $0, function_trace_stop

	jne  ftrace_stub



	cmpq $ftrace_stub, ftrace_trace_function

	jnz trace

.globl ftrace_stub

include/linux/ftrace.h

+30 −0
Original line number Diff line number Diff line
@@ -23,6 +23,34 @@ struct ftrace_ops { 
	struct ftrace_ops *next;

};



extern int function_trace_stop;



/**

 * ftrace_stop - stop function tracer.

 *

 * A quick way to stop the function tracer. Note this an on off switch,

 * it is not something that is recursive like preempt_disable.

 * This does not disable the calling of mcount, it only stops the

 * calling of functions from mcount.

 */

static inline void ftrace_stop(void)

{

	function_trace_stop = 1;

}



/**

 * ftrace_start - start the function tracer.

 *

 * This function is the inverse of ftrace_stop. This does not enable

 * the function tracing if the function tracer is disabled. This only

 * sets the function tracer flag to continue calling the functions

 * from mcount.

 */

static inline void ftrace_start(void)

{

	function_trace_stop = 0;

}



/*

 * The ftrace_ops must be a static and should also

 * be read_mostly.  These functions do modify read_mostly variables
@@ -41,6 +69,8 @@ extern void ftrace_stub(unsigned long a0, unsigned long a1); 
# define unregister_ftrace_function(ops) do { } while (0)

# define clear_ftrace_function(ops) do { } while (0)

static inline void ftrace_kill(void) { }

static inline void ftrace_stop(void) { }

static inline void ftrace_start(void) { }

#endif /* CONFIG_FUNCTION_TRACER */



#ifdef CONFIG_DYNAMIC_FTRACE

kernel/trace/Kconfig

+7 −0
Original line number Diff line number Diff line
@@ -9,6 +9,13 @@ config NOP_TRACER 
config HAVE_FUNCTION_TRACER

	bool



config HAVE_FUNCTION_TRACE_MCOUNT_TEST

	bool

	help

	 This gets selected when the arch tests the function_trace_stop

	 variable at the mcount call site. Otherwise, this variable

	 is tested by the called function.



config HAVE_DYNAMIC_FTRACE

	bool

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