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, 42 insertions, 0 deletions

diff --git a/Documentation/rust/index.rst b/Documentation/rust/index.rst
new file mode 100644
index 000000000..b78ed0efa
--- /dev/null
+++ b/Documentation/rust/index.rst
@@ -0,0 +1,42 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Rust
+====
+
+Documentation related to Rust within the kernel. To start using Rust
+in the kernel, please read the quick-start.rst guide.
+
+
+Code documentation
+------------------
+
+Given a kernel configuration, the kernel may generate Rust code documentation,
+i.e. HTML rendered by the ``rustdoc`` tool.
+
+.. only:: rustdoc and html
+
+	This kernel documentation was built with `Rust code documentation
+	<rustdoc/kernel/index.html>`_.
+
+.. only:: not rustdoc and html
+
+	This kernel documentation was not built with Rust code documentation.
+
+A pregenerated version is provided at:
+
+	https://rust.docs.kernel.org
+
+Please see the :ref:`Code documentation <rust_code_documentation>` section for
+more details.
+
+.. toctree::
+    :maxdepth: 1
+
+    quick-start
+    general-information
+    coding-guidelines
+    arch-support
+    testing
+
+You can also find learning materials for Rust in its section in
+:doc:`../process/kernel-docs`.