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, 39 insertions, 0 deletions

diff --git a/Documentation/usb/functionfs-desc.rst b/Documentation/usb/functionfs-desc.rst
new file mode 100644
index 000000000..39649774d
--- /dev/null
+++ b/Documentation/usb/functionfs-desc.rst
@@ -0,0 +1,39 @@
+======================
+FunctionFS Descriptors
+======================
+
+Some of the descriptors that can be written to the FFS gadget are
+described below. Device and configuration descriptors are handled
+by the composite gadget and are not written by the user to the
+FFS gadget.
+
+Descriptors are written to the "ep0" file in the FFS gadget
+following the descriptor header.
+
+.. kernel-doc:: include/uapi/linux/usb/functionfs.h
+   :doc: descriptors
+
+Interface Descriptors
+---------------------
+
+Standard USB interface descriptors may be written. The class/subclass of the
+most recent interface descriptor determines what type of class-specific
+descriptors are accepted.
+
+Class-Specific Descriptors
+--------------------------
+
+Class-specific descriptors are accepted only for the class/subclass of the
+most recent interface descriptor. The following are some of the
+class-specific descriptors that are supported.
+
+DFU Functional Descriptor
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When the interface class is USB_CLASS_APP_SPEC and the interface subclass
+is USB_SUBCLASS_DFU, a DFU functional descriptor can be provided.
+The DFU functional descriptor is a described in the USB specification for
+Device Firmware Upgrade (DFU), version 1.1 as of this writing.
+
+.. kernel-doc:: include/uapi/linux/usb/functionfs.h
+   :doc: usb_dfu_functional_descriptor