Commit 1fd8df2c authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt
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tracing/kprobes: Fix kprobe-tracer to support stack trace 



Fix to support kernel stack trace correctly on kprobe-tracer.
Since the execution path of kprobe-based dynamic events is different
from other tracepoint-based events, normal ftrace_trace_stack() doesn't
work correctly. To fix that, this introduces ftrace_trace_stack_regs()
which traces stack via pt_regs instead of current stack register.

e.g.

 # echo p schedule+4 > /sys/kernel/debug/tracing/kprobe_events
 # echo 1 > /sys/kernel/debug/tracing/options/stacktrace
 # echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
 # head -n 20 /sys/kernel/debug/tracing/trace
            bash-2968  [000] 10297.050245: p_schedule_4: (schedule+0x4/0x4ca)
            bash-2968  [000] 10297.050247: <stack trace>
 => schedule_timeout
 => n_tty_read
 => tty_read
 => vfs_read
 => sys_read
 => system_call_fastpath
     kworker/0:1-2940  [000] 10297.050265: p_schedule_4: (schedule+0x4/0x4ca)
     kworker/0:1-2940  [000] 10297.050266: <stack trace>
 => worker_thread
 => kthread
 => kernel_thread_helper
            sshd-1132  [000] 10297.050365: p_schedule_4: (schedule+0x4/0x4ca)
            sshd-1132  [000] 10297.050365: <stack trace>
 => sysret_careful

Note: Even with this fix, the first entry will be skipped
if the probe is put on the function entry area before
the frame pointer is set up (usually, that is 4 bytes
 (push %bp; mov %sp %bp) on x86), because stack unwinder
depends on the frame pointer.

Signed-off-by: default avatarMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: yrl.pp-manager.tt@hitachi.com
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Namhyung Kim <namhyung@gmail.com>
Link: http://lkml.kernel.org/r/20110608070934.17777.17116.stgit@fedora15


Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent c624d33f

include/linux/ftrace_event.h

+4 −0
Original line number Diff line number Diff line
@@ -129,6 +129,10 @@ void trace_current_buffer_unlock_commit(struct ring_buffer *buffer, 
void trace_nowake_buffer_unlock_commit(struct ring_buffer *buffer,

				       struct ring_buffer_event *event,

					unsigned long flags, int pc);

void trace_nowake_buffer_unlock_commit_regs(struct ring_buffer *buffer,

					    struct ring_buffer_event *event,

					    unsigned long flags, int pc,

					    struct pt_regs *regs);

void trace_current_buffer_discard_commit(struct ring_buffer *buffer,

					 struct ring_buffer_event *event);

kernel/trace/trace.c

+29 −5
Original line number Diff line number Diff line
@@ -1193,6 +1193,18 @@ void trace_nowake_buffer_unlock_commit(struct ring_buffer *buffer, 
}

EXPORT_SYMBOL_GPL(trace_nowake_buffer_unlock_commit);



void trace_nowake_buffer_unlock_commit_regs(struct ring_buffer *buffer,

					    struct ring_buffer_event *event,

					    unsigned long flags, int pc,

					    struct pt_regs *regs)

{

	ring_buffer_unlock_commit(buffer, event);



	ftrace_trace_stack_regs(buffer, flags, 0, pc, regs);

	ftrace_trace_userstack(buffer, flags, pc);

}

EXPORT_SYMBOL_GPL(trace_nowake_buffer_unlock_commit_regs);



void trace_current_buffer_discard_commit(struct ring_buffer *buffer,

					 struct ring_buffer_event *event)

{
@@ -1238,7 +1250,7 @@ ftrace(struct trace_array *tr, struct trace_array_cpu *data, 
#ifdef CONFIG_STACKTRACE

static void __ftrace_trace_stack(struct ring_buffer *buffer,

				 unsigned long flags,

				 int skip, int pc)

				 int skip, int pc, struct pt_regs *regs)

{

	struct ftrace_event_call *call = &event_kernel_stack;

	struct ring_buffer_event *event;
@@ -1257,24 +1269,36 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer, 
	trace.skip		= skip;

	trace.entries		= entry->caller;



	if (regs)

		save_stack_trace_regs(regs, &trace);

	else

		save_stack_trace(&trace);

	if (!filter_check_discard(call, entry, buffer, event))

		ring_buffer_unlock_commit(buffer, event);

}



void ftrace_trace_stack_regs(struct ring_buffer *buffer, unsigned long flags,

			     int skip, int pc, struct pt_regs *regs)

{

	if (!(trace_flags & TRACE_ITER_STACKTRACE))

		return;



	__ftrace_trace_stack(buffer, flags, skip, pc, regs);

}



void ftrace_trace_stack(struct ring_buffer *buffer, unsigned long flags,

			int skip, int pc)

{

	if (!(trace_flags & TRACE_ITER_STACKTRACE))

		return;



	__ftrace_trace_stack(buffer, flags, skip, pc);

	__ftrace_trace_stack(buffer, flags, skip, pc, NULL);

}



void __trace_stack(struct trace_array *tr, unsigned long flags, int skip,

		   int pc)

{

	__ftrace_trace_stack(tr->buffer, flags, skip, pc);

	__ftrace_trace_stack(tr->buffer, flags, skip, pc, NULL);

}



/**
@@ -1290,7 +1314,7 @@ void trace_dump_stack(void) 
	local_save_flags(flags);



	/* skipping 3 traces, seems to get us at the caller of this function */

	__ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count());

	__ftrace_trace_stack(global_trace.buffer, flags, 3, preempt_count(), NULL);

}



static DEFINE_PER_CPU(int, user_stack_count);

kernel/trace/trace.h

+9 −0
Original line number Diff line number Diff line
@@ -389,6 +389,9 @@ void update_max_tr_single(struct trace_array *tr, 
void ftrace_trace_stack(struct ring_buffer *buffer, unsigned long flags,

			int skip, int pc);



void ftrace_trace_stack_regs(struct ring_buffer *buffer, unsigned long flags,

			     int skip, int pc, struct pt_regs *regs);



void ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags,

			    int pc);
@@ -400,6 +403,12 @@ static inline void ftrace_trace_stack(struct ring_buffer *buffer, 
{

}



static inline void ftrace_trace_stack_regs(struct ring_buffer *buffer,

					   unsigned long flags, int skip,

					   int pc, struct pt_regs *regs)

{

}



static inline void ftrace_trace_userstack(struct ring_buffer *buffer,

					  unsigned long flags, int pc)

{

kernel/trace/trace_kprobe.c

+4 −2
Original line number Diff line number Diff line
@@ -1397,7 +1397,8 @@ static __kprobes void kprobe_trace_func(struct kprobe *kp, struct pt_regs *regs) 
	store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);



	if (!filter_current_check_discard(buffer, call, entry, event))

		trace_nowake_buffer_unlock_commit(buffer, event, irq_flags, pc);

		trace_nowake_buffer_unlock_commit_regs(buffer, event,

						       irq_flags, pc, regs);

}



/* Kretprobe handler */
@@ -1429,7 +1430,8 @@ static __kprobes void kretprobe_trace_func(struct kretprobe_instance *ri, 
	store_trace_args(sizeof(*entry), tp, regs, (u8 *)&entry[1], dsize);



	if (!filter_current_check_discard(buffer, call, entry, event))

		trace_nowake_buffer_unlock_commit(buffer, event, irq_flags, pc);

		trace_nowake_buffer_unlock_commit_regs(buffer, event,

						       irq_flags, pc, regs);

}



/* Event entry printers */

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