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, 53 insertions, 0 deletions

diff --git a/Documentation/driver-api/spi.rst b/Documentation/driver-api/spi.rst
new file mode 100644
index 000000000..74eca6735
--- /dev/null
+++ b/Documentation/driver-api/spi.rst
@@ -0,0 +1,53 @@
+Serial Peripheral Interface (SPI)
+=================================
+
+SPI is the "Serial Peripheral Interface", widely used with embedded
+systems because it is a simple and efficient interface: basically a
+multiplexed shift register. Its three signal wires hold a clock (SCK,
+often in the range of 1-20 MHz), a "Master Out, Slave In" (MOSI) data
+line, and a "Master In, Slave Out" (MISO) data line. SPI is a full
+duplex protocol; for each bit shifted out the MOSI line (one per clock)
+another is shifted in on the MISO line. Those bits are assembled into
+words of various sizes on the way to and from system memory. An
+additional chipselect line is usually active-low (nCS); four signals are
+normally used for each peripheral, plus sometimes an interrupt.
+
+The SPI bus facilities listed here provide a generalized interface to
+declare SPI buses and devices, manage them according to the standard
+Linux driver model, and perform input/output operations. At this time,
+only "master" side interfaces are supported, where Linux talks to SPI
+peripherals and does not implement such a peripheral itself. (Interfaces
+to support implementing SPI slaves would necessarily look different.)
+
+The programming interface is structured around two kinds of driver, and
+two kinds of device. A "Controller Driver" abstracts the controller
+hardware, which may be as simple as a set of GPIO pins or as complex as
+a pair of FIFOs connected to dual DMA engines on the other side of the
+SPI shift register (maximizing throughput). Such drivers bridge between
+whatever bus they sit on (often the platform bus) and SPI, and expose
+the SPI side of their device as a :c:type:`struct spi_controller
+<spi_controller>`. SPI devices are children of that master,
+represented as a :c:type:`struct spi_device <spi_device>` and
+manufactured from :c:type:`struct spi_board_info
+<spi_board_info>` descriptors which are usually provided by
+board-specific initialization code. A :c:type:`struct spi_driver
+<spi_driver>` is called a "Protocol Driver", and is bound to a
+spi_device using normal driver model calls.
+
+The I/O model is a set of queued messages. Protocol drivers submit one
+or more :c:type:`struct spi_message <spi_message>` objects,
+which are processed and completed asynchronously. (There are synchronous
+wrappers, however.) Messages are built from one or more
+:c:type:`struct spi_transfer <spi_transfer>` objects, each of
+which wraps a full duplex SPI transfer. A variety of protocol tweaking
+options are needed, because different chips adopt very different
+policies for how they use the bits transferred with SPI.
+
+.. kernel-doc:: include/linux/spi/spi.h
+   :internal:
+
+.. kernel-doc:: drivers/spi/spi.c
+   :functions: spi_register_board_info
+
+.. kernel-doc:: drivers/spi/spi.c
+   :export: