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, 160 insertions, 0 deletions

diff --git a/tools/perf/tests/kallsyms-split.c b/tools/perf/tests/kallsyms-split.c
new file mode 100644
index 000000000..244daa01b
--- /dev/null
+++ b/tools/perf/tests/kallsyms-split.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include "util/dso.h"
+#include "util/map.h"
+#include "util/symbol.h"
+#include "util/debug.h"
+#include "util/machine.h"
+#include "tests.h"
+
+/*
+ * This test is to check whether a bad symbol in a module won't split kallsyms maps.
+ * The main_symbol[1-3] should belong to the main [kernel.kallsyms] map even if the
+ * bad_symbol from the module is found in the middle.
+ */
+static char root_template[] = "/tmp/perf-test.XXXXXX";
+static char *root_dir;
+
+static const char proc_version[] = "Linux version X.Y.Z (just for perf test)\n";
+static const char proc_modules[] = "module 4096 1 - Live 0xffffffffcd000000\n";
+static const char proc_kallsyms[] =
+	"ffffffffab200000 T _stext\n"
+	"ffffffffab200010 T good_symbol\n"
+	"ffffffffab200020 t bad_symbol\n"
+	"ffffffffab200030 t main_symbol1\n"
+	"ffffffffab200040 t main_symbol2\n"
+	"ffffffffab200050 t main_symbol3\n"
+	"ffffffffab200060 T _etext\n"
+	"ffffffffcd000000 T start_module\t[module]\n"
+	"ffffffffab200020 u bad_symbol\t[module]\n"
+	"ffffffffcd000040 T end_module\t[module]\n";
+
+static struct {
+	const char *name;
+	const char *contents;
+	long len;
+} proc_files[] = {
+	{ "version", proc_version, sizeof(proc_version) - 1 },
+	{ "modules", proc_modules, sizeof(proc_modules) - 1 },
+	{ "kallsyms", proc_kallsyms, sizeof(proc_kallsyms) - 1 },
+};
+
+static void remove_proc_dir(int sig __maybe_unused)
+{
+	char buf[128];
+
+	if (root_dir == NULL)
+		return;
+
+	for (unsigned i = 0; i < ARRAY_SIZE(proc_files); i++) {
+		scnprintf(buf, sizeof(buf), "%s/proc/%s", root_dir, proc_files[i].name);
+		remove(buf);
+	}
+
+	scnprintf(buf, sizeof(buf), "%s/proc", root_dir);
+	rmdir(buf);
+
+	rmdir(root_dir);
+	root_dir = NULL;
+}
+
+static int create_proc_dir(void)
+{
+	char buf[128];
+
+	root_dir = mkdtemp(root_template);
+	if (root_dir == NULL)
+		return -1;
+
+	scnprintf(buf, sizeof(buf), "%s/proc", root_dir);
+	if (mkdir(buf, 0700) < 0)
+		goto err;
+
+	for (unsigned i = 0; i < ARRAY_SIZE(proc_files); i++) {
+		int fd, len;
+
+		scnprintf(buf, sizeof(buf), "%s/proc/%s", root_dir, proc_files[i].name);
+		fd = open(buf, O_RDWR | O_CREAT, 0600);
+		if (fd < 0)
+			goto err;
+
+		len = write(fd, proc_files[i].contents, proc_files[i].len);
+		close(fd);
+		if (len != proc_files[i].len)
+			goto err;
+	}
+	return 0;
+
+err:
+	remove_proc_dir(0);
+	return -1;
+}
+
+static int test__kallsyms_split(struct test_suite *test __maybe_unused,
+				int subtest __maybe_unused)
+{
+	struct machine m = { 0 };
+	struct map *map = NULL;
+	int ret = TEST_FAIL;
+
+	pr_debug("try to create fake root directory\n");
+	if (create_proc_dir() < 0) {
+		pr_debug("SKIP: cannot create a fake root directory\n");
+		return TEST_SKIP;
+	}
+
+	signal(SIGINT, remove_proc_dir);
+	signal(SIGPIPE, remove_proc_dir);
+	signal(SIGSEGV, remove_proc_dir);
+	signal(SIGTERM, remove_proc_dir);
+
+	pr_debug("create kernel maps from the fake root directory\n");
+	if (machine__init(&m, root_dir, HOST_KERNEL_ID)) {
+		pr_debug("FAIL: failed to init machine\n");
+		goto out;
+	}
+	if (machine__create_kernel_maps(&m) < 0) {
+		pr_debug("FAIL: failed to create kernel maps\n");
+		goto out;
+	}
+
+	/* force to use /proc/kallsyms */
+	symbol_conf.ignore_vmlinux = true;
+	symbol_conf.ignore_vmlinux_buildid = true;
+	symbol_conf.allow_aliases = true;
+
+	if (map__load(machine__kernel_map(&m)) < 0) {
+		pr_debug("FAIL: failed to load kallsyms\n");
+		goto out;
+	}
+
+	pr_debug("kernel map loaded - check symbol and map\n");
+	if (maps__nr_maps(machine__kernel_maps(&m)) != 2) {
+		pr_debug("FAIL: it should have the kernel and a module, but has %u maps\n",
+			 maps__nr_maps(machine__kernel_maps(&m)));
+		goto out;
+	}
+
+	if (machine__find_kernel_symbol_by_name(&m, "main_symbol3", &map) == NULL) {
+		pr_debug("FAIL: failed to find a symbol\n");
+		goto out;
+	}
+
+	if (!RC_CHK_EQUAL(map, machine__kernel_map(&m))) {
+		pr_debug("FAIL: the symbol is not in the kernel map\n");
+		goto out;
+	}
+	ret = TEST_OK;
+
+out:
+	map__put(map);
+	remove_proc_dir(0);
+	machine__exit(&m);
+	return ret;
+}
+
+DEFINE_SUITE("split kallsyms", kallsyms_split);