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Message-ID: <20241007113537.19686-1-jeff.xie@linux.dev>
Date: Mon, 7 Oct 2024 19:35:37 +0800
From: Jeff Xie <jeff.xie@...ux.dev>
To: rostedt@...dmis.org,
mhiramat@...nel.org
Cc: mathieu.desnoyers@...icios.com,
linux-trace-kernel@...r.kernel.org,
linux-kernel@...r.kernel.org,
xiehuan09@...il.com,
dolinux.peng@...il.com,
chensong_2000@....cn,
Jeff Xie <jeff.xie@...ux.dev>
Subject: [PATCH v4] ftrace: Get the true parent ip for function tracer
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@...ux.dev>
---
v4:
https://lore.kernel.org/linux-trace-kernel/20241005101320.766c1100@rorschach.local.home/
- fixed the crash when accessing the "current" if the arch has not implemented noinstr
thanks steve for the testing and the detailed explanation
v3:
https://lore.kernel.org/linux-trace-kernel/20240910001326.87f27e6b312f1d956cf352a2@kernel.org/
- fixed build error when CONFIG_FUNCTION_GRAPH_TRACER=n suggested by Masami
v2:
https://lore.kernel.org/linux-trace-kernel/20240821095910.1888d7fa@gandalf.local.home/
- 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..46b663d22c37 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);
}
+#if defined(CONFIG_FUNCTION_GRAPH_TRACER) && defined(CONFIG_ARCH_WANTS_NO_INSTR)
+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
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