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, 100 insertions, 0 deletions

diff --git a/tools/perf/tests/thread-maps-share.c b/tools/perf/tests/thread-maps-share.c
new file mode 100644
index 000000000..0431bff31
--- /dev/null
+++ b/tools/perf/tests/thread-maps-share.c
@@ -0,0 +1,100 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "tests.h"
+#include "machine.h"
+#include "thread.h"
+#include "debug.h"
+
+static int test__thread_maps_share(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct machines machines;
+	struct machine *machine;
+
+	/* thread group */
+	struct thread *leader;
+	struct thread *t1, *t2, *t3;
+	struct maps *maps;
+
+	/* other process */
+	struct thread *other, *other_leader;
+	struct maps *other_maps;
+
+	/*
+	 * This test create 2 processes abstractions (struct thread)
+	 * with several threads and checks they properly share and
+	 * maintain maps info (struct maps).
+	 *
+	 * thread group (pid: 0, tids: 0, 1, 2, 3)
+	 * other  group (pid: 4, tids: 4, 5)
+	*/
+
+	TEST_ASSERT_VAL("failed to init machines", machines__init(&machines) == 0);
+	machine = &machines.host;
+
+	/* create process with 4 threads */
+	leader = machine__findnew_thread(machine, 0, 0);
+	t1     = machine__findnew_thread(machine, 0, 1);
+	t2     = machine__findnew_thread(machine, 0, 2);
+	t3     = machine__findnew_thread(machine, 0, 3);
+
+	/* and create 1 separated process, without thread leader */
+	other  = machine__findnew_thread(machine, 4, 5);
+
+	TEST_ASSERT_VAL("failed to create threads",
+			leader && t1 && t2 && t3 && other);
+
+	maps = thread__maps(leader);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 4);
+
+	/* test the maps pointer is shared */
+	TEST_ASSERT_VAL("maps don't match", maps__equal(maps, thread__maps(t1)));
+	TEST_ASSERT_VAL("maps don't match", maps__equal(maps, thread__maps(t2)));
+	TEST_ASSERT_VAL("maps don't match", maps__equal(maps, thread__maps(t3)));
+
+	/*
+	 * Verify the other leader was created by previous call.
+	 * It should have shared maps with no change in
+	 * refcnt.
+	 */
+	other_leader = machine__find_thread(machine, 4, 4);
+	TEST_ASSERT_VAL("failed to find other leader", other_leader);
+
+	/*
+	 * Ok, now that all the rbtree related operations were done,
+	 * lets remove all of them from there so that we can do the
+	 * refcounting tests.
+	 */
+	machine__remove_thread(machine, leader);
+	machine__remove_thread(machine, t1);
+	machine__remove_thread(machine, t2);
+	machine__remove_thread(machine, t3);
+	machine__remove_thread(machine, other);
+	machine__remove_thread(machine, other_leader);
+
+	other_maps = thread__maps(other);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(other_maps)), 2);
+
+	TEST_ASSERT_VAL("maps don't match", maps__equal(other_maps, thread__maps(other_leader)));
+
+	/* release thread group */
+	thread__put(t3);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 3);
+
+	thread__put(t2);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 2);
+
+	thread__put(t1);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 1);
+
+	thread__put(leader);
+
+	/* release other group  */
+	thread__put(other_leader);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(other_maps)), 1);
+
+	thread__put(other);
+
+	machines__exit(&machines);
+	return 0;
+}
+
+DEFINE_SUITE("Share thread maps", thread_maps_share);