linux-kernel - Re: [RFC 2/3] arm64: refactor save_stack

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Date:	Thu, 16 Jul 2015 09:27:46 +0900
From:	AKASHI Takahiro <takahiro.akashi@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Jungseok Lee <jungseoklee85@...il.com>, catalin.marinas@....com,
	will.deacon@....com, olof@...om.net, broonie@...nel.org,
	david.griego@...aro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/3] arm64: refactor save_stack_trace()

On 07/16/2015 01:13 AM, Steven Rostedt wrote:
> On Wed, 15 Jul 2015 10:55:36 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
>
>
>> I'll take a look at it and try to clean up the code.
>
> Does the  following patch make sense for you?

Looks nice. The patch greatly simplifies changes on arm64 side.

- Takahiro AKASHI

> -- Steve
>
> diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
> index 3f34496244e9..9384647d07c3 100644
> --- a/kernel/trace/trace_stack.c
> +++ b/kernel/trace/trace_stack.c
> @@ -18,12 +18,6 @@
>
>   #define STACK_TRACE_ENTRIES 500
>
> -#ifdef CC_USING_FENTRY
> -# define fentry		1
> -#else
> -# define fentry		0
> -#endif
> -
>   static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES+1] =
>   	 { [0 ... (STACK_TRACE_ENTRIES)] = ULONG_MAX };
>   static unsigned stack_dump_index[STACK_TRACE_ENTRIES];
> @@ -35,7 +29,7 @@ static unsigned stack_dump_index[STACK_TRACE_ENTRIES];
>    */
>   static struct stack_trace max_stack_trace = {
>   	.max_entries		= STACK_TRACE_ENTRIES - 1,
> -	.entries		= &stack_dump_trace[1],
> +	.entries		= &stack_dump_trace[0],
>   };
>
>   static unsigned long max_stack_size;
> @@ -77,7 +71,7 @@ check_stack(unsigned long ip, unsigned long *stack)
>   	unsigned long this_size, flags; unsigned long *p, *top, *start;
>   	static int tracer_frame;
>   	int frame_size = ACCESS_ONCE(tracer_frame);
> -	int i;
> +	int i, x;
>
>   	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
>   	this_size = THREAD_SIZE - this_size;
> @@ -105,26 +99,20 @@ check_stack(unsigned long ip, unsigned long *stack)
>   	max_stack_size = this_size;
>
>   	max_stack_trace.nr_entries = 0;
> -
> -	if (using_ftrace_ops_list_func())
> -		max_stack_trace.skip = 4;
> -	else
> -		max_stack_trace.skip = 3;
> +	max_stack_trace.skip = 0;
>
>   	save_stack_trace(&max_stack_trace);
>
> -	/*
> -	 * Add the passed in ip from the function tracer.
> -	 * Searching for this on the stack will skip over
> -	 * most of the overhead from the stack tracer itself.
> -	 */
> -	stack_dump_trace[0] = ip;
> -	max_stack_trace.nr_entries++;
> +	/* Skip over the overhead of the stack tracer itself */
> +	for (i = 0; i < max_stack_trace.nr_entries; i++) {
> +		if (stack_dump_trace[i] == ip)
> +			break;
> +	}
>
>   	/*
>   	 * Now find where in the stack these are.
>   	 */
> -	i = 0;
> +	x = 0;
>   	start = stack;
>   	top = (unsigned long *)
>   		(((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);
> @@ -139,12 +127,13 @@ check_stack(unsigned long ip, unsigned long *stack)
>   	while (i < max_stack_trace.nr_entries) {
>   		int found = 0;
>
> -		stack_dump_index[i] = this_size;
> +		stack_dump_index[x] = this_size;
>   		p = start;
>
>   		for (; p < top && i < max_stack_trace.nr_entries; p++) {
>   			if (*p == stack_dump_trace[i]) {
> -				this_size = stack_dump_index[i++] =
> +				stack_dump_trace[x] = stack_dump_trace[i++];
> +				this_size = stack_dump_index[x++] =
>   					(top - p) * sizeof(unsigned long);
>   				found = 1;
>   				/* Start the search from here */
> @@ -168,6 +157,9 @@ check_stack(unsigned long ip, unsigned long *stack)
>   			i++;
>   	}
>
> +	for (; x < max_stack_trace.nr_entries; x++)
> +		stack_dump_trace[x] = ULONG_MAX;
> +
>   	if (task_stack_end_corrupted(current)) {
>   		print_max_stack();
>   		BUG();
> @@ -192,24 +184,7 @@ stack_trace_call(unsigned long ip, unsigned long parent_ip,
>   	if (per_cpu(trace_active, cpu)++ != 0)
>   		goto out;
>
> -	/*
> -	 * When fentry is used, the traced function does not get
> -	 * its stack frame set up, and we lose the parent.
> -	 * The ip is pretty useless because the function tracer
> -	 * was called before that function set up its stack frame.
> -	 * In this case, we use the parent ip.
> -	 *
> -	 * By adding the return address of either the parent ip
> -	 * or the current ip we can disregard most of the stack usage
> -	 * caused by the stack tracer itself.
> -	 *
> -	 * The function tracer always reports the address of where the
> -	 * mcount call was, but the stack will hold the return address.
> -	 */
> -	if (fentry)
> -		ip = parent_ip;
> -	else
> -		ip += MCOUNT_INSN_SIZE;
> +	ip += MCOUNT_INSN_SIZE;
>
>   	check_stack(ip, &stack);
>
>
--
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