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Since commit 79922b8009c07 ("ftrace: Optimize function graph to be
called directly"), dynamic trampolines should not be calling the
function graph tracer at the end. If they do, it could cause the function
graph tracer to trace functions that it filtered out.
Right now it does not cause a problem because there's a test to check if
the function graph tracer is attached to the same function as the
function tracer, which for now is true. But the function graph tracer is
undergoing changes that can make this no longer true which will cause
the function graph tracer to trace other functions.
For example:
# cd /sys/kernel/tracing/
# echo do_IRQ > set_ftrace_filter
# mkdir instances/foo
# echo ip_rcv > instances/foo/set_ftrace_filter
# echo function_graph > current_tracer
# echo function > instances/foo/current_tracer
Would cause the function graph tracer to trace both do_IRQ and ip_rcv,
if the current tests change.
As the current tests prevent this from being a problem, this code does
not need to be backported. But it does make the code cleaner.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Signed-off-by: Steven Rostedt (VMware) <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 Restructured Text 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.