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, 26 insertions, 0 deletions

diff --git a/Documentation/i2c/slave-eeprom-backend.rst b/Documentation/i2c/slave-eeprom-backend.rst
new file mode 100644
index 000000000..38d951f10
--- /dev/null
+++ b/Documentation/i2c/slave-eeprom-backend.rst
@@ -0,0 +1,26 @@
+==============================
+Linux I2C slave EEPROM backend
+==============================
+
+by Wolfram Sang <wsa@sang-engineering.com> in 2014-20
+
+This backend simulates an EEPROM on the connected I2C bus. Its memory contents
+can be accessed from userspace via this file located in sysfs::
+
+	/sys/bus/i2c/devices/<device-directory>/slave-eeprom
+
+The following types are available: 24c02, 24c32, 24c64, and 24c512. Read-only
+variants are also supported. The name needed for instantiating has the form
+'slave-<type>[ro]'. Examples follow:
+
+24c02, read/write, address 0x64:
+  # echo slave-24c02 0x1064 > /sys/bus/i2c/devices/i2c-1/new_device
+
+24c512, read-only, address 0x42:
+  # echo slave-24c512ro 0x1042 > /sys/bus/i2c/devices/i2c-1/new_device
+
+You can also preload data during boot if a device-property named
+'firmware-name' contains a valid filename (DT or ACPI only).
+
+As of 2015, Linux doesn't support poll on binary sysfs files, so there is no
+notification when another master changed the content.