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Message-ID: <55A6FA82.9000901@linaro.org>
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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