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, 43 insertions, 0 deletions

diff --git a/Documentation/input/devices/cs461x.rst b/Documentation/input/devices/cs461x.rst
new file mode 100644
index 000000000..b1e6d508a
--- /dev/null
+++ b/Documentation/input/devices/cs461x.rst
@@ -0,0 +1,43 @@
+Crystal SoundFusion CS4610/CS4612/CS461 joystick
+================================================
+
+This is a new low-level driver to support analog joystick attached to
+Crystal SoundFusion CS4610/CS4612/CS4615. This code is based upon
+Vortex/Solo drivers as an example of decoration style, and ALSA
+0.5.8a kernel drivers as an chipset documentation and samples.
+
+This version does not have cooked mode support; the basic code
+is present here, but have not tested completely. The button analysis
+is completed in this mode, but the axis movement is not.
+
+Raw mode works fine with analog joystick front-end driver and cs461x
+driver as a backend. I've tested this driver with CS4610, 4-axis and
+4-button joystick; I mean the jstest utility. Also I've tried to
+play in xracer game using joystick, and the result is better than
+keyboard only mode.
+
+The sensitivity and calibrate quality have not been tested; the two
+reasons are performed: the same hardware cannot work under Win95 (blue
+screen in VJOYD); I have no documentation on my chip; and the existing
+behavior in my case was not raised the requirement of joystick calibration.
+So the driver have no code to perform hardware related calibration.
+
+This driver have the basic support for PCI devices only; there is no
+ISA or PnP ISA cards supported.
+
+The driver works with ALSA drivers simultaneously. For example, the xracer
+uses joystick as input device and PCM device as sound output in one time.
+There are no sound or input collisions detected. The source code have
+comments about them; but I've found the joystick can be initialized
+separately of ALSA modules. So, you can use only one joystick driver
+without ALSA drivers. The ALSA drivers are not needed to compile or
+run this driver.
+
+There are no debug information print have been placed in source, and no
+specific options required to work this driver. The found chipset parameters
+are printed via printk(KERN_INFO "..."), see the /var/log/messages to
+inspect cs461x: prefixed messages to determine possible card detection
+errors.
+
+Regards,
+Viktor