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, 41 insertions, 0 deletions

diff --git a/Documentation/arch/powerpc/elfnote.rst b/Documentation/arch/powerpc/elfnote.rst
new file mode 100644
index 000000000..3ec8d61e9
--- /dev/null
+++ b/Documentation/arch/powerpc/elfnote.rst
@@ -0,0 +1,41 @@
+==========================
+ELF Note PowerPC Namespace
+==========================
+
+The PowerPC namespace in an ELF Note of the kernel binary is used to store
+capabilities and information which can be used by a bootloader or userland.
+
+Types and Descriptors
+---------------------
+
+The types to be used with the "PowerPC" namespace are defined in [#f1]_.
+
+	1) PPC_ELFNOTE_CAPABILITIES
+
+Define the capabilities supported/required by the kernel. This type uses a
+bitmap as "descriptor" field. Each bit is described below:
+
+- Ultravisor-capable bit (PowerNV only).
+
+.. code-block:: c
+
+	#define PPCCAP_ULTRAVISOR_BIT (1 << 0)
+
+Indicate that the powerpc kernel binary knows how to run in an
+ultravisor-enabled system.
+
+In an ultravisor-enabled system, some machine resources are now controlled
+by the ultravisor. If the kernel is not ultravisor-capable, but it ends up
+being run on a machine with ultravisor, the kernel will probably crash
+trying to access ultravisor resources. For instance, it may crash in early
+boot trying to set the partition table entry 0.
+
+In an ultravisor-enabled system, a bootloader could warn the user or prevent
+the kernel from being run if the PowerPC ultravisor capability doesn't exist
+or the Ultravisor-capable bit is not set.
+
+References
+----------
+
+.. [#f1] arch/powerpc/include/asm/elfnote.h
+