Re: [PATCH -tip ] [BUGFIX]tracing/kprobes: Fix kprobe-tracer to supportstack trace

[Masami Hiramatsu]

(2011/05/12 19:22), Masami Hiramatsu wrote:
> 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.

Hmm, any comments?

> 
> e.g.
> 
>  # echo p schedule > /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
> # tracer: nop
> #
> #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
> #              | |       |          |         |
>             sshd-1549  [001]   857.326335: p_schedule_0: (schedule+0x0/0x900)
>             sshd-1549  [001]   857.326337: <stack trace>
>  => schedule_hrtimeout_range
>  => poll_schedule_timeout
>  => do_select
>  => core_sys_select
>  => sys_select
>  => system_call_fastpath
>              tee-1751  [000]   857.326394: p_schedule_0: (schedule+0x0/0x900)
>              tee-1751  [000]   857.326395: <stack trace>
>  => do_group_exit
>  => sys_exit_group
>  => system_call_fastpath
>           <idle>-0     [001]   857.326406: p_schedule_0: (schedule+0x0/0x900)
>           <idle>-0     [001]   857.326407: <stack trace>
>  => start_secondary
> 
> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  include/linux/ftrace_event.h |    4 ++++
>  kernel/trace/trace.c         |   35 ++++++++++++++++++++++++++++++-----
>  kernel/trace/trace.h         |    9 +++++++++
>  kernel/trace/trace_kprobe.c  |    6 ++++--
>  4 files changed, 47 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index b5a550a..bca2499 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -117,6 +117,10 @@ 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);
>  
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ee9c921..bf12209 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -1191,6 +1191,18 @@ 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)
>  {
> @@ -1236,7 +1248,7 @@ 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;
> @@ -1255,24 +1267,36 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
>  	trace.skip		= skip;
>  	trace.entries		= entry->caller;
>  
> -	save_stack_trace(&trace);
> +	if (regs)
> +		save_stack_trace_regs(&trace, regs);
> +	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);
>  }
>  
>  /**
> @@ -1288,7 +1312,8 @@ 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);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 5e9dfc6..cbce5e4 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -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)
>  {
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index f925c45..7053ef3 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -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 */
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@xxxxxxxxxxx
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