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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/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>
Link: https://lore.kernel.org/20241008033159.22459-1-jeff.xie@linux.dev
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jeff Xie <jeff.xie@linux.dev>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.