Re: [PATCH v3] ftrace: Get the true parent ip for function tracer

[jeff.xie@linux.dev]

September 10, 2024 at 9:36 PM, "Jeff Xie" <jeff.xie@linux.dev> wrote:

Kindly ping...

> 
> When using both function tracer and function graph simultaneously,
> 
> it is found that function tracer sometimes captures a fake parent ip
> 
> (return_to_handler) instead of the true parent ip.
> 
> This issue is easy to reproduce. Below are my reproduction steps:
> 
> jeff-labs:~/bin # ./trace-net.sh
> 
> jeff-labs:~/bin # cat /sys/kernel/debug/tracing/instances/foo/trace | grep return_to_handler
> 
>  trace-net.sh-405 [001] ...2. 31.859501: avc_has_perm+0x4/0x190 <-return_to_handler+0x0/0x40
> 
>  trace-net.sh-405 [001] ...2. 31.859503: simple_setattr+0x4/0x70 <-return_to_handler+0x0/0x40
> 
>  trace-net.sh-405 [001] ...2. 31.859503: truncate_pagecache+0x4/0x60 <-return_to_handler+0x0/0x40
> 
>  trace-net.sh-405 [001] ...2. 31.859505: unmap_mapping_range+0x4/0x140 <-return_to_handler+0x0/0x40
> 
>  trace-net.sh-405 [001] ...3. 31.859508: _raw_spin_unlock+0x4/0x30 <-return_to_handler+0x0/0x40
> 
>  [...]
> 
> The following is my simple trace script:
> 
> <snip>
> 
> jeff-labs:~/bin # cat ./trace-net.sh
> 
> TRACE_PATH="/sys/kernel/debug/tracing"
> 
> set_events() {
> 
>  echo 1 > $1/events/net/enable
> 
>  echo 1 > $1/events/tcp/enable
> 
>  echo 1 > $1/events/sock/enable
> 
>  echo 1 > $1/events/napi/enable
> 
>  echo 1 > $1/events/fib/enable
> 
>  echo 1 > $1/events/neigh/enable
> 
> }
> 
> set_events ${TRACE_PATH}
> 
> echo 1 > ${TRACE_PATH}/options/sym-offset
> 
> echo 1 > ${TRACE_PATH}/options/funcgraph-tail
> 
> echo 1 > ${TRACE_PATH}/options/funcgraph-proc
> 
> echo 1 > ${TRACE_PATH}/options/funcgraph-abstime
> 
> echo 'tcp_orphan*' > ${TRACE_PATH}/set_ftrace_notrace
> 
> echo function_graph > ${TRACE_PATH}/current_tracer
> 
> INSTANCE_FOO=${TRACE_PATH}/instances/foo
> 
> if [ ! -e $INSTANCE_FOO ]; then
> 
>  mkdir ${INSTANCE_FOO}
> 
> fi
> 
> set_events ${INSTANCE_FOO}
> 
> echo 1 > ${INSTANCE_FOO}/options/sym-offset
> 
> echo 'tcp_orphan*' > ${INSTANCE_FOO}/set_ftrace_notrace
> 
> echo function > ${INSTANCE_FOO}/current_tracer
> 
> echo 1 > ${TRACE_PATH}/tracing_on
> 
> echo 1 > ${INSTANCE_FOO}/tracing_on
> 
> echo > ${TRACE_PATH}/trace
> 
> echo > ${INSTANCE_FOO}/trace
> 
> </snip>
> 
> Signed-off-by: Jeff Xie <jeff.xie@linux.dev>
> 
> ---
> 
> v3:
> 
> - fixed build error when CONFIG_FUNCTION_GRAPH_TRACER=n suggested by Masami
> 
> v2:
> 
> - Adding __always_inline to function_get_true_parent_ip suggested by Steve
> 
>  kernel/trace/trace_functions.c | 26 ++++++++++++++++++++++++++
> 
>  1 file changed, 26 insertions(+)
> 
> diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
> 
> index 3b0cea37e029..5dc5fcdf4e6f 100644
> 
> --- a/kernel/trace/trace_functions.c
> 
> +++ b/kernel/trace/trace_functions.c
> 
> @@ -176,6 +176,27 @@ static void function_trace_start(struct trace_array *tr)
> 
>  tracing_reset_online_cpus(&tr->array_buffer);
> 
>  }
> 
>  
> 
> +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
> 
> +static __always_inline unsigned long
> 
> +function_get_true_parent_ip(unsigned long parent_ip, struct ftrace_regs *fregs)
> 
> +{
> 
> + unsigned long true_parent_ip;
> 
> + int idx = 0;
> 
> +
> 
> + true_parent_ip = parent_ip;
> 
> + if (unlikely(parent_ip == (unsigned long)&return_to_handler))
> 
> + true_parent_ip = ftrace_graph_ret_addr(current, &idx, parent_ip,
> 
> + (unsigned long *)fregs->regs.sp);
> 
> + return true_parent_ip;
> 
> +}
> 
> +#else
> 
> +static __always_inline unsigned long
> 
> +function_get_true_parent_ip(unsigned long parent_ip, struct ftrace_regs *fregs)
> 
> +{
> 
> + return parent_ip;
> 
> +}
> 
> +#endif
> 
> +
> 
>  static void
> 
>  function_trace_call(unsigned long ip, unsigned long parent_ip,
> 
>  struct ftrace_ops *op, struct ftrace_regs *fregs)
> 
> @@ -193,6 +214,8 @@ function_trace_call(unsigned long ip, unsigned long parent_ip,
> 
>  if (bit < 0)
> 
>  return;
> 
>  
> 
> + parent_ip = function_get_true_parent_ip(parent_ip, fregs);
> 
> +
> 
>  trace_ctx = tracing_gen_ctx();
> 
>  
> 
>  cpu = smp_processor_id();
> 
> @@ -241,6 +264,7 @@ function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
> 
>  * recursive protection is performed.
> 
>  */
> 
>  local_irq_save(flags);
> 
> + parent_ip = function_get_true_parent_ip(parent_ip, fregs);
> 
>  cpu = raw_smp_processor_id();
> 
>  data = per_cpu_ptr(tr->array_buffer.data, cpu);
> 
>  disabled = atomic_inc_return(&data->disabled);
> 
> @@ -309,6 +333,7 @@ function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> 
>  if (bit < 0)
> 
>  return;
> 
>  
> 
> + parent_ip = function_get_true_parent_ip(parent_ip, fregs);
> 
>  cpu = smp_processor_id();
> 
>  data = per_cpu_ptr(tr->array_buffer.data, cpu);
> 
>  if (atomic_read(&data->disabled))
> 
> @@ -356,6 +381,7 @@ function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
> 
>  * recursive protection is performed.
> 
>  */
> 
>  local_irq_save(flags);
> 
> + parent_ip = function_get_true_parent_ip(parent_ip, fregs);
> 
>  cpu = raw_smp_processor_id();
> 
>  data = per_cpu_ptr(tr->array_buffer.data, cpu);
> 
>  disabled = atomic_inc_return(&data->disabled);
> 
> -- 
> 
> 2.43.0
>