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, 107 insertions, 0 deletions

diff --git a/rust/compiler_builtins.rs b/rust/compiler_builtins.rs
new file mode 100644
index 000000000..fc6b54636
--- /dev/null
+++ b/rust/compiler_builtins.rs
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Our own `compiler_builtins`.
+//!
+//! Rust provides [`compiler_builtins`] as a port of LLVM's [`compiler-rt`].
+//! Since we do not need the vast majority of them, we avoid the dependency
+//! by providing this file.
+//!
+//! At the moment, some builtins are required that should not be. For instance,
+//! [`core`] has 128-bit integers functionality which we should not be compiling
+//! in. We will work with upstream [`core`] to provide feature flags to disable
+//! the parts we do not need. For the moment, we define them to [`panic!`] at
+//! runtime for simplicity to catch mistakes, instead of performing surgery
+//! on `core.o`.
+//!
+//! In any case, all these symbols are weakened to ensure we do not override
+//! those that may be provided by the rest of the kernel.
+//!
+//! [`compiler_builtins`]: https://github.com/rust-lang/compiler-builtins
+//! [`compiler-rt`]: https://compiler-rt.llvm.org/
+
+#![allow(internal_features)]
+#![feature(compiler_builtins)]
+#![compiler_builtins]
+#![no_builtins]
+#![no_std]
+
+macro_rules! define_panicking_intrinsics(
+    ($reason: tt, { $($ident: ident, )* }) => {
+        $(
+            #[doc(hidden)]
+            #[export_name = concat!("__rust", stringify!($ident))]
+            pub extern "C" fn $ident() {
+                panic!($reason);
+            }
+        )*
+    }
+);
+
+define_panicking_intrinsics!("`f32` should not be used", {
+    __addsf3,
+    __eqsf2,
+    __extendsfdf2,
+    __gesf2,
+    __lesf2,
+    __ltsf2,
+    __mulsf3,
+    __nesf2,
+    __truncdfsf2,
+    __unordsf2,
+});
+
+define_panicking_intrinsics!("`f64` should not be used", {
+    __adddf3,
+    __eqdf2,
+    __ledf2,
+    __ltdf2,
+    __muldf3,
+    __unorddf2,
+});
+
+define_panicking_intrinsics!("`i128` should not be used", {
+    __ashrti3,
+    __muloti4,
+    __multi3,
+});
+
+define_panicking_intrinsics!("`u128` should not be used", {
+    __ashlti3,
+    __lshrti3,
+    __udivmodti4,
+    __udivti3,
+    __umodti3,
+});
+
+#[cfg(target_arch = "arm")]
+define_panicking_intrinsics!("`f32` should not be used", {
+    __aeabi_fadd,
+    __aeabi_fmul,
+    __aeabi_fcmpeq,
+    __aeabi_fcmple,
+    __aeabi_fcmplt,
+    __aeabi_fcmpun,
+});
+
+#[cfg(target_arch = "arm")]
+define_panicking_intrinsics!("`f64` should not be used", {
+    __aeabi_dadd,
+    __aeabi_dmul,
+    __aeabi_dcmple,
+    __aeabi_dcmplt,
+    __aeabi_dcmpun,
+});
+
+#[cfg(target_arch = "arm")]
+define_panicking_intrinsics!("`u64` division/modulo should not be used", {
+    __aeabi_uldivmod,
+});
+
+#[cfg(target_arch = "powerpc")]
+define_panicking_intrinsics!("`u64` division/modulo should not be used", {
+    __udivdi3,
+    __umoddi3,
+});
+
+// NOTE: if you are adding a new intrinsic here, you should also add it to
+// `redirect-intrinsics` in `rust/Makefile`.