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, 17 insertions, 0 deletions

diff --git a/tools/perf/util/smt.h b/tools/perf/util/smt.h
new file mode 100644
index 000000000..01441fd2c
--- /dev/null
+++ b/tools/perf/util/smt.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __SMT_H
+#define __SMT_H 1
+
+/*
+ * Returns true if SMT (aka hyperthreading) is enabled. Determined via sysfs or
+ * the online topology.
+ */
+bool smt_on(void);
+
+/*
+ * Returns true when system wide and all SMT threads for a core are in the
+ * user_requested_cpus map.
+ */
+bool core_wide(bool system_wide, const char *user_requested_cpu_list);
+
+#endif /* __SMT_H */