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, 109 insertions, 0 deletions

diff --git a/Documentation/admin-guide/media/raspberrypi-pisp-be.rst b/Documentation/admin-guide/media/raspberrypi-pisp-be.rst
new file mode 100644
index 000000000..0fcf46f26
--- /dev/null
+++ b/Documentation/admin-guide/media/raspberrypi-pisp-be.rst
@@ -0,0 +1,109 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=========================================================
+Raspberry Pi PiSP Back End Memory-to-Memory ISP (pisp-be)
+=========================================================
+
+The PiSP Back End
+=================
+
+The PiSP Back End is a memory-to-memory Image Signal Processor (ISP) which reads
+image data from DRAM memory and performs image processing as specified by the
+application through the parameters in a configuration buffer, before writing
+pixel data back to memory through two distinct output channels.
+
+The ISP registers and programming model are documented in the `Raspberry Pi
+Image Signal Processor (PiSP) Specification document`_
+
+The PiSP Back End ISP processes images in tiles. The handling of image
+tessellation and the computation of low-level configuration parameters is
+realized by a free software library called `libpisp
+<https://github.com/raspberrypi/libpisp>`_.
+
+The full image processing pipeline, which involves capturing RAW Bayer data from
+an image sensor through a MIPI CSI-2 compatible capture interface, storing them
+in DRAM memory and processing them in the PiSP Back End to obtain images usable
+by an application is implemented in `libcamera <https://libcamera.org>`_ as
+part of the Raspberry Pi platform support.
+
+The pisp-be driver
+==================
+
+The Raspberry Pi PiSP Back End (pisp-be) driver is located under
+drivers/media/platform/raspberrypi/pisp-be. It uses the `V4L2 API` to register
+a number of video capture and output devices, the `V4L2 subdev API` to register
+a subdevice for the ISP that connects the video devices in a single media graph
+realized using the `Media Controller (MC) API`.
+
+The media topology registered by the `pisp-be` driver is represented below:
+
+.. _pips-be-topology:
+
+.. kernel-figure:: raspberrypi-pisp-be.dot
+    :alt:   Diagram of the default media pipeline topology
+    :align: center
+
+
+The media graph registers the following video device nodes:
+
+- pispbe-input: output device for images to be submitted to the ISP for
+  processing.
+- pispbe-tdn_input: output device for temporal denoise.
+- pispbe-stitch_input: output device for image stitching (HDR).
+- pispbe-output0: first capture device for processed images.
+- pispbe-output1: second capture device for processed images.
+- pispbe-tdn_output: capture device for temporal denoise.
+- pispbe-stitch_output: capture device for image stitching (HDR).
+- pispbe-config: output device for ISP configuration parameters.
+
+pispbe-input
+------------
+
+Images to be processed by the ISP are queued to the `pispbe-input` output device
+node. For a list of image formats supported as input to the ISP refer to the
+`Raspberry Pi Image Signal Processor (PiSP) Specification document`_.
+
+pispbe-tdn_input, pispbe-tdn_output
+-----------------------------------
+
+The `pispbe-tdn_input` output video device receives images to be processed by
+the temporal denoise block which are captured from the `pispbe-tdn_output`
+capture video device. Userspace is responsible for maintaining queues on both
+devices, and ensuring that buffers completed on the output are queued to the
+input.
+
+pispbe-stitch_input, pispbe-stitch_output
+-----------------------------------------
+
+To realize HDR (high dynamic range) image processing the image stitching and
+tonemapping blocks are used. The `pispbe-stitch_output` writes images to memory
+and the `pispbe-stitch_input` receives the previously written frame to process
+it along with the current input image. Userspace is responsible for maintaining
+queues on both devices, and ensuring that buffers completed on the output are
+queued to the input.
+
+pispbe-output0, pispbe-output1
+------------------------------
+
+The two capture devices write to memory the pixel data as processed by the ISP.
+
+pispbe-config
+-------------
+
+The `pispbe-config` output video devices receives a buffer of configuration
+parameters that define the desired image processing to be performed by the ISP.
+
+The format of the ISP configuration parameter is defined by
+:c:type:`pisp_be_tiles_config` C structure and the meaning of each parameter is
+described in the `Raspberry Pi Image Signal Processor (PiSP) Specification
+document`_.
+
+ISP configuration
+=================
+
+The ISP configuration is described solely by the content of the parameters
+buffer. The only parameter that userspace needs to configure using the V4L2 API
+is the image format on the output and capture video devices for validation of
+the content of the parameters buffer.
+
+.. _Raspberry Pi Image Signal Processor (PiSP) Specification document: https://datasheets.raspberrypi.com/camera/raspberry-pi-image-signal-processor-specification.pdf