linux-kernel - Re: [PATCH] ftrace/arm: add save_stack_trace

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Message-ID: <20140423090355.5a0a98cd@gandalf.local.home>
Date:	Wed, 23 Apr 2014 09:03:55 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Lin Yongting <linyongting@...il.com>
Cc:	linux@....linux.org.uk, k.khlebnikov@...sung.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linyongting@...wei.com
Subject: Re: [PATCH] ftrace/arm: add save_stack_trace_regs() implementation

On Wed, 23 Apr 2014 20:52:21 +0800
Lin Yongting <linyongting@...il.com> wrote:

> When configure kprobe events of ftrace with "stacktrace" option enabled
> in arm, there is no stacktrace was recorded after the kprobe event was
> triggered. The root cause is no save_stack_trace_regs() function implemented.
> 
> Implement the save_stack_trace_regs() function in arm, then ftrace will
> call this architecture-related function to record the stacktrace into
> ring buffer.
> 
> After this fix, stacktrace can be recorded, for example:
> 
> # mount -t debugfs nodev /sys/kernel/debug
> # echo "p:netrx net_rx_action" >> /sys/kernel/debug/tracing/kprobe_events
> # echo 1 > /sys/kernel/debug/tracing/events/kprobes/netrx/enable
> # echo 1 > /sys/kernel/debug/tracing/options/stacktrace
> # echo 1 > /sys/kernel/debug/tracing/tracing_on
> # ping 127.0.0.1 -c 1
> # echo 0 > /sys/kernel/debug/tracing/tracing_on
> 
> # cat /sys/kernel/debug/tracing/trace
> # tracer: nop
> #
> # entries-in-buffer/entries-written: 12/12   #P:1
> #
> #                              _-----=> irqs-off
> #                             / _----=> need-resched
> #                            | / _---=> hardirq/softirq
> #                            || / _--=> preempt-depth
> #                            ||| /     delay
> #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> #              | |       |   ||||       |         |
>             <------ missing some entries ---------------->
>             ping-1200  [000] dNs1   667.603250: netrx: (net_rx_action+0x0/0x1f8)
>             ping-1200  [000] dNs1   667.604738: <stack trace>
>  => net_rx_action
>  => do_softirq
>  => local_bh_enable
>  => ip_finish_output
>  => ip_output
>  => ip_local_out
>  => ip_send_skb
>  => ip_push_pending_frames
>  => raw_sendmsg
>  => inet_sendmsg
>  => sock_sendmsg
>  => SyS_sendto
>  => ret_fast_syscall
> 
> Signed-off-by: Lin Yongting <linyongting@...il.com>
> ---

As this affects ftrace for ARM...

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

>  arch/arm/kernel/stacktrace.c |   19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/arch/arm/kernel/stacktrace.c b/arch/arm/kernel/stacktrace.c
> index af4e8c8..c558db6 100644
> --- a/arch/arm/kernel/stacktrace.c
> +++ b/arch/arm/kernel/stacktrace.c
> @@ -123,6 +123,25 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
>  		trace->entries[trace->nr_entries++] = ULONG_MAX;
>  }
>  
> +void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
> +{
> +	struct stack_trace_data data;
> +	struct stackframe frame;
> +
> +	data.trace = trace;
> +	data.skip = trace->skip;
> +	data.no_sched_functions = 0;
> +
> +	frame.fp = regs->ARM_fp;
> +	frame.sp = regs->ARM_sp;
> +	frame.lr = regs->ARM_lr;
> +	frame.pc = regs->ARM_pc;
> +
> +	walk_stackframe(&frame, save_trace, &data);
> +	if (trace->nr_entries < trace->max_entries)
> +		trace->entries[trace->nr_entries++] = ULONG_MAX;
> +}
> +
>  void save_stack_trace(struct stack_trace *trace)
>  {
>  	save_stack_trace_tsk(current, trace);

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