From 4617721c502b2ddaa4e324e86da4997edf738fa5 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 2 Sep 2026 09:55:01 -0400 Subject: ftrace: Synchronize the initialization of ftrace_ops 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 --- Documentation/driver-api/gpio/using-gpio.rst | 50 ++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 Documentation/driver-api/gpio/using-gpio.rst (limited to 'Documentation/driver-api/gpio/using-gpio.rst') diff --git a/Documentation/driver-api/gpio/using-gpio.rst b/Documentation/driver-api/gpio/using-gpio.rst new file mode 100644 index 000000000..894d88855 --- /dev/null +++ b/Documentation/driver-api/gpio/using-gpio.rst @@ -0,0 +1,50 @@ +========================= +Using GPIO Lines in Linux +========================= + +The Linux kernel exists to abstract and present hardware to users. GPIO lines +as such are normally not user facing abstractions. The most obvious, natural +and preferred way to use GPIO lines is to let kernel hardware drivers deal +with them. + +For examples of already existing generic drivers that will also be good +examples for any other kernel drivers you want to author, refer to +Documentation/driver-api/gpio/drivers-on-gpio.rst + +For any kind of mass produced system you want to support, such as servers, +laptops, phones, tablets, routers, and any consumer or office or business goods +using appropriate kernel drivers is paramount. Submit your code for inclusion +in the upstream Linux kernel when you feel it is mature enough and you will get +help to refine it, see Documentation/process/submitting-patches.rst. + +In Linux GPIO lines also have a userspace ABI. + +The userspace ABI is intended for one-off deployments. Examples are prototypes, +factory lines, maker community projects, workshop specimen, production tools, +industrial automation, PLC-type use cases, door controllers, in short a piece +of specialized equipment that is not produced by the numbers, requiring +operators to have a deep knowledge of the equipment and knows about the +software-hardware interface to be set up. They should not have a natural fit +to any existing kernel subsystem and not be a good fit for an operating system, +because of not being reusable or abstract enough, or involving a lot of non +computer hardware related policy. + +Applications that have a good reason to use the industrial I/O (IIO) subsystem +from userspace will likely be a good fit for using GPIO lines from userspace as +well. + +Do not under any circumstances abuse the GPIO userspace ABI to cut corners in +any product development projects. If you use it for prototyping, then do not +productify the prototype: rewrite it using proper kernel drivers. Do not under +any circumstances deploy any uniform products using GPIO from userspace. + +The userspace ABI is a character device for each GPIO hardware unit (GPIO chip). +These devices will appear on the system as ``/dev/gpiochip0`` thru +``/dev/gpiochipN``. Examples of how to directly use the userspace ABI can be +found in the kernel tree ``tools/gpio`` subdirectory. + +For structured and managed applications, we recommend that you make use of the +libgpiod_ library. This provides helper abstractions, command line utilities +and arbitration for multiple simultaneous consumers on the same GPIO chip. + +.. _libgpiod: https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/ -- cgit v1.3.1