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, 46 insertions, 0 deletions

diff --git a/Documentation/userspace-api/media/intro.rst b/Documentation/userspace-api/media/intro.rst
new file mode 100644
index 000000000..4a6bd665b
--- /dev/null
+++ b/Documentation/userspace-api/media/intro.rst
@@ -0,0 +1,46 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+============
+Introduction
+============
+
+This document covers the Linux Kernel to Userspace API's used by video
+and radio streaming devices, including video cameras, analog and digital
+TV receiver cards, AM/FM receiver cards, Software Defined Radio (SDR),
+streaming capture and output devices, codec devices and remote controllers.
+
+A typical media device hardware is shown at :ref:`typical_media_device`.
+
+.. _typical_media_device:
+
+.. kernel-figure:: typical_media_device.svg
+    :alt:   typical_media_device.svg
+    :align: center
+
+    Typical Media Device
+
+The media infrastructure API was designed to control such devices. It is
+divided into five parts.
+
+1. The :ref:`first part <v4l2spec>` covers radio, video capture and output,
+   cameras, analog TV devices and codecs.
+
+2. The :ref:`second part <dvbapi>` covers the API used for digital TV and
+   Internet reception via one of the several digital tv standards. While it is
+   called as DVB API, in fact it covers several different video standards
+   including DVB-T/T2, DVB-S/S2, DVB-C, ATSC, ISDB-T, ISDB-S, DTMB, etc. The
+   complete list of supported standards can be found at
+   :c:type:`fe_delivery_system`.
+
+3. The :ref:`third part <remote_controllers>` covers the Remote Controller API.
+
+4. The :ref:`fourth part <media_controller>` covers the Media Controller API.
+
+5. The :ref:`fifth part <cec>` covers the CEC (Consumer Electronics Control) API.
+
+It should also be noted that a media device may also have audio components, like
+mixers, PCM capture, PCM playback, etc, which are controlled via ALSA API.  For
+additional information and for the latest development code, see:
+`https://linuxtv.org <https://linuxtv.org>`__.  For discussing improvements,
+reporting troubles, sending new drivers, etc, please mail to: `Linux Media
+Mailing List (LMML) <http://vger.kernel.org/vger-lists.html#linux-media>`__.