ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 194 insertions, 0 deletions

diff --git a/tools/perf/util/setup.py b/tools/perf/util/setup.py
new file mode 100644
index 000000000..8380980ad
--- /dev/null
+++ b/tools/perf/util/setup.py
@@ -0,0 +1,194 @@
+# SPDX-License-Identifier: GPL-2.0
+"""Setup script for perf python extension.
+
+This script is used to build and install the perf python binding.
+It handles compiler-specific flags, especially for clang, and configures
+the setuptools Extension.
+"""
+
+import os
+import shlex
+import shutil
+import subprocess
+import sysconfig
+
+from setuptools import setup, Extension
+from setuptools.command.build_ext import build_ext as _build_ext
+from setuptools.command.install_lib import install_lib as _install_lib
+
+
+def clang_has_option(cc: str, cc_args: list[str], src_feature_tests: str, option: str) -> bool:
+    """Check if clang supports a specific option.
+
+    Args:
+        cc: The compiler executable.
+        cc_args: Compiler arguments from CC environment variable.
+        src_feature_tests: Path to the feature tests directory.
+        option: The compiler option to check (e.g., "-mcet").
+
+    Returns:
+        True if the option is supported, False otherwise.
+    """
+    error_substrings = (
+        b"unknown argument",
+        b"is not supported",
+        b"unknown warning option"
+    )
+    cmd = [cc] + cc_args + [
+        option,
+        "-o", "/dev/null",
+        os.path.join(src_feature_tests, "test-hello.c")
+    ]
+    try:
+        res = subprocess.run(cmd, stderr=subprocess.PIPE, stdout=subprocess.DEVNULL, check=False)
+        cc_output = res.stderr.splitlines()
+    except OSError:
+        return False
+    return not any(any(error in line for error in error_substrings) for line in cc_output)
+
+
+def filter_clang_options(cc: str, cc_args: list[str], src_feature_tests: str) -> None:
+    """Filter out unsupported clang options from sysconfig CFLAGS and OPT.
+
+    Args:
+        cc: The compiler executable.
+        cc_args: Compiler arguments from CC environment variable.
+        src_feature_tests: Path to the feature tests directory.
+    """
+    config_vars = sysconfig.get_config_vars()
+    for var in ('CFLAGS', 'OPT'):
+        if var not in config_vars:
+            continue
+
+        # Split into individual flags using shlex to preserve quoted arguments
+        flags = shlex.split(config_vars[var])
+
+        # Remove -specs=...
+        flags = [f for f in flags if not f.startswith("-specs=")]
+
+        options = (
+            "-mcet",
+            "-fcf-protection",
+            "-fstack-clash-protection",
+            "-fstack-protector-strong",
+            "-fno-semantic-interposition",
+            "-ffat-lto-objects",
+            "-ftree-loop-distribute-patterns",
+            "-gno-variable-location-views"
+        )
+        for option in options:
+            if not clang_has_option(cc, cc_args, src_feature_tests, option):
+                # Remove the option and any variant (e.g. -option=...)
+                flags = [f for f in flags if not f.startswith(option)]
+
+        # Re-join flags preserving quoting
+        config_vars[var] = shlex.join(flags)
+
+
+class BuildExt(_build_ext):
+    """Custom build_ext command to set output directories."""
+
+    def __init__(self, *args, **kwargs):
+        self.build_lib = None
+        self.build_temp = None
+        super().__init__(*args, **kwargs)
+
+    def finalize_options(self) -> None:
+        _build_ext.finalize_options(self)
+        build_lib = os.getenv('PYTHON_EXTBUILD_LIB')
+        build_tmp = os.getenv('PYTHON_EXTBUILD_TMP')
+        if build_lib:
+            self.build_lib = build_lib
+        if build_tmp:
+            self.build_temp = build_tmp
+
+
+class InstallLib(_install_lib):
+    """Custom install_lib command to set output directory."""
+
+    def __init__(self, *args, **kwargs):
+        self.build_dir = None
+        super().__init__(*args, **kwargs)
+
+    def finalize_options(self) -> None:
+        _install_lib.finalize_options(self)
+        build_lib = os.getenv('PYTHON_EXTBUILD_LIB')
+        if build_lib:
+            self.build_dir = build_lib
+
+    def run(self):
+        _install_lib.run(self)
+        srctree = os.getenv('srctree', '.')
+        src_perf = os.path.join(srctree, 'tools/perf')
+        shutil.copy2(os.path.join(src_perf, 'python/perf.pyi'), self.install_dir)
+
+
+def main() -> None:
+    """Main entry point for the setup script."""
+    cc_env = os.getenv("CC")
+    assert cc_env, "Environment variable CC not set"
+
+    # Safe parsing of CC environment variable which might contain options/quotes
+    cc_tokens = shlex.split(cc_env)
+    cc = cc_tokens[0]
+    cc_args = cc_tokens[1:]
+
+    # Run CC -v to check if it is clang.
+    try:
+        cc_info = subprocess.run(
+            [cc, "-v"], stderr=subprocess.PIPE, stdout=subprocess.DEVNULL, check=False
+        )
+        cc_is_clang = b"clang version" in cc_info.stderr
+    except OSError as e:
+        raise RuntimeError(f"Failed to execute compiler '{cc}': {e}") from e
+
+    srctree = os.getenv('srctree')
+    assert srctree, "Environment variable srctree, for the Linux sources, not set"
+    src_feature_tests = f'{srctree}/tools/build/feature'
+
+    if cc_is_clang:
+        filter_clang_options(cc, cc_args, src_feature_tests)
+
+    # switch off several checks (need to be at the end of cflags list)
+    cflags = [
+        '-fno-strict-aliasing',
+        '-Wno-write-strings',
+        '-Wno-unused-parameter',
+        '-Wno-redundant-decls'
+    ]
+    if cc_is_clang:
+        cflags += ["-Wno-unused-command-line-argument"]
+        if clang_has_option(
+            cc, cc_args, src_feature_tests, "-Wno-cast-function-type-mismatch"
+        ):
+            cflags += ["-Wno-cast-function-type-mismatch"]
+    else:
+        cflags += ['-Wno-cast-function-type']
+
+    # The python headers have mixed code with declarations (decls after asserts, for instance)
+    cflags += ["-Wno-declaration-after-statement"]
+
+    src_perf = f'{srctree}/tools/perf'
+
+    perf = Extension(
+        'perf',
+        sources=[os.path.join(src_perf, 'util/python.c')],
+        include_dirs=['util/include'],
+        extra_compile_args=cflags,
+    )
+
+    setup(
+        name='perf',
+        version='0.1',
+        description='Interface with the Linux profiling infrastructure',
+        author='Arnaldo Carvalho de Melo',
+        author_email='acme@redhat.com',
+        license='GPLv2',
+        url='http://perf.wiki.kernel.org',
+        ext_modules=[perf],
+        cmdclass={'build_ext': BuildExt, 'install_lib': InstallLib},
+    )
+
+
+if __name__ == '__main__':
+    main()