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SubjectRe: [RFC][PATCH 02/14] fgraph: Have set_graph_notrace only affect function_graph tracer
Hi Steve,

On Wed, Nov 21, 2018 at 08:27:10PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
>
> In order to make the function graph infrastructure more generic, there can
> not be code specific for the function_graph tracer in the generic code. This
> includes the set_graph_notrace logic, that stops all graph calls when a
> function in the set_graph_notrace is hit.
>
> By using the trace_recursion mask, we can use a bit in the current
> task_struct to implement the notrace code, and move the logic out of
> fgraph.c and into trace_functions_graph.c and keeps it affecting only the
> tracer and not all call graph callbacks.
>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung


> ---
> kernel/trace/fgraph.c | 21 ---------------------
> kernel/trace/trace.h | 6 ++++++
> kernel/trace/trace_functions_graph.c | 21 +++++++++++++++++++++
> 3 files changed, 27 insertions(+), 21 deletions(-)
>
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index e8fcf1b2b38c..c684968b87e7 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -64,30 +64,9 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func,
> return -EBUSY;
> }
>
> - /*
> - * The curr_ret_stack is an index to ftrace return stack of
> - * current task. Its value should be in [0, FTRACE_RETFUNC_
> - * DEPTH) when the function graph tracer is used. To support
> - * filtering out specific functions, it makes the index
> - * negative by subtracting huge value (FTRACE_NOTRACE_DEPTH)
> - * so when it sees a negative index the ftrace will ignore
> - * the record. And the index gets recovered when returning
> - * from the filtered function by adding the FTRACE_NOTRACE_
> - * DEPTH and then it'll continue to record functions normally.
> - *
> - * The curr_ret_stack is initialized to -1 and get increased
> - * in this function. So it can be less than -1 only if it was
> - * filtered out via ftrace_graph_notrace_addr() which can be
> - * set from set_graph_notrace file in tracefs by user.
> - */
> - if (current->curr_ret_stack < -1)
> - return -EBUSY;
> -
> calltime = trace_clock_local();
>
> index = ++current->curr_ret_stack;
> - if (ftrace_graph_notrace_addr(func))
> - current->curr_ret_stack -= FTRACE_NOTRACE_DEPTH;
> barrier();
> current->ret_stack[index].ret = ret;
> current->ret_stack[index].func = func;
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 3b8c0e24ab30..f3ad85830961 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -512,6 +512,12 @@ enum {
> * can only be modified by current, we can reuse trace_recursion.
> */
> TRACE_IRQ_BIT,
> +/*
> + * To implement set_graph_notrace, if this bit is set, we ignore
> + * function graph tracing of called functions, until the return
> + * function is called to clear it.
> + */
> + TRACE_GRAPH_NOTRACE_BIT,
> };
>
> #define trace_recursion_set(bit) do { (current)->trace_recursion |= (1<<(bit)); } while (0)
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index af1759cd6eab..4748dc1bf5e1 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -188,6 +188,18 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)
> int cpu;
> int pc;
>
> + if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT))
> + return 0;
> +
> + if (ftrace_graph_notrace_addr(trace->func)) {
> + trace_recursion_set(TRACE_GRAPH_NOTRACE_BIT);
> + /*
> + * Need to return 1 to have the return called
> + * that will clear the NOTRACE bit.
> + */
> + return 1;
> + }
> +
> if (!ftrace_trace_task(tr))
> return 0;
>
> @@ -288,6 +300,11 @@ void trace_graph_return(struct ftrace_graph_ret *trace)
> int cpu;
> int pc;
>
> + if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT)) {
> + trace_recursion_clear(TRACE_GRAPH_NOTRACE_BIT);
> + return;
> + }
> +
> local_irq_save(flags);
> cpu = raw_smp_processor_id();
> data = per_cpu_ptr(tr->trace_buffer.data, cpu);
> @@ -311,6 +328,10 @@ void set_graph_array(struct trace_array *tr)
>
> static void trace_graph_thresh_return(struct ftrace_graph_ret *trace)
> {
> + if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT)) {
> + trace_recursion_clear(TRACE_GRAPH_NOTRACE_BIT);
> + return;
> + }
> if (tracing_thresh &&
> (trace->rettime - trace->calltime < tracing_thresh))
> return;
> --
> 2.19.1
>
>

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