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, 136 insertions, 0 deletions

diff --git a/Documentation/misc-devices/max6875.rst b/Documentation/misc-devices/max6875.rst
new file mode 100644
index 000000000..ad419ac22
--- /dev/null
+++ b/Documentation/misc-devices/max6875.rst
@@ -0,0 +1,136 @@
+=====================
+Kernel driver max6875
+=====================
+
+Supported chips:
+
+  * Maxim MAX6874, MAX6875
+
+    Prefix: 'max6875'
+
+    Addresses scanned: None (see below)
+
+    Datasheet: http://pdfserv.maxim-ic.com/en/ds/MAX6874-MAX6875.pdf
+
+Author: Ben Gardner <bgardner@wabtec.com>
+
+
+Description
+-----------
+
+The Maxim MAX6875 is an EEPROM-programmable power-supply sequencer/supervisor.
+It provides timed outputs that can be used as a watchdog, if properly wired.
+It also provides 512 bytes of user EEPROM.
+
+At reset, the MAX6875 reads the configuration EEPROM into its configuration
+registers.  The chip then begins to operate according to the values in the
+registers.
+
+The Maxim MAX6874 is a similar, mostly compatible device, with more inputs
+and outputs:
+
+===========  ===     ===    ====
+-            vin     gpi    vout
+===========  ===     ===    ====
+MAX6874        6       4       8
+MAX6875        4       3       5
+===========  ===     ===    ====
+
+See the datasheet for more information.
+
+
+Sysfs entries
+-------------
+
+eeprom        - 512 bytes of user-defined EEPROM space.
+
+
+General Remarks
+---------------
+
+Valid addresses for the MAX6875 are 0x50 and 0x52.
+
+Valid addresses for the MAX6874 are 0x50, 0x52, 0x54 and 0x56.
+
+The driver does not probe any address, so you explicitly instantiate the
+devices.
+
+Example::
+
+  $ modprobe max6875
+  $ echo max6875 0x50 > /sys/bus/i2c/devices/i2c-0/new_device
+
+The MAX6874/MAX6875 ignores address bit 0, so this driver attaches to multiple
+addresses.  For example, for address 0x50, it also reserves 0x51.
+The even-address instance is called 'max6875', the odd one is 'dummy'.
+
+
+Programming the chip using i2c-dev
+----------------------------------
+
+Use the i2c-dev interface to access and program the chips.
+
+Reads and writes are performed differently depending on the address range.
+
+The configuration registers are at addresses 0x00 - 0x45.
+
+Use i2c_smbus_write_byte_data() to write a register and
+i2c_smbus_read_byte_data() to read a register.
+
+The command is the register number.
+
+Examples:
+
+To write a 1 to register 0x45::
+
+  i2c_smbus_write_byte_data(fd, 0x45, 1);
+
+To read register 0x45::
+
+  value = i2c_smbus_read_byte_data(fd, 0x45);
+
+
+The configuration EEPROM is at addresses 0x8000 - 0x8045.
+
+The user EEPROM is at addresses 0x8100 - 0x82ff.
+
+Use i2c_smbus_write_word_data() to write a byte to EEPROM.
+
+The command is the upper byte of the address: 0x80, 0x81, or 0x82.
+The data word is the lower part of the address or'd with data << 8::
+
+  cmd = address >> 8;
+  val = (address & 0xff) | (data << 8);
+
+Example:
+
+To write 0x5a to address 0x8003::
+
+  i2c_smbus_write_word_data(fd, 0x80, 0x5a03);
+
+
+Reading data from the EEPROM is a little more complicated.
+
+Use i2c_smbus_write_byte_data() to set the read address and then
+i2c_smbus_read_byte() or i2c_smbus_read_i2c_block_data() to read the data.
+
+Example:
+
+To read data starting at offset 0x8100, first set the address::
+
+  i2c_smbus_write_byte_data(fd, 0x81, 0x00);
+
+And then read the data::
+
+  value = i2c_smbus_read_byte(fd);
+
+or::
+
+  count = i2c_smbus_read_i2c_block_data(fd, 0x84, 16, buffer);
+
+The block read should read 16 bytes.
+
+0x84 is the block read command.
+
+See the datasheet for more details.
+