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, 109 insertions, 0 deletions

diff --git a/Documentation/tools/rtla/rtla-hwnoise.rst b/Documentation/tools/rtla/rtla-hwnoise.rst
new file mode 100644
index 000000000..5930bbca4
--- /dev/null
+++ b/Documentation/tools/rtla/rtla-hwnoise.rst
@@ -0,0 +1,109 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. |tool| replace:: hwnoise
+
+============
+rtla-hwnoise
+============
+------------------------------------------
+Detect and quantify hardware-related noise
+------------------------------------------
+
+:Manual section: 1
+
+SYNOPSIS
+========
+
+**rtla hwnoise** [*OPTIONS*]
+
+DESCRIPTION
+===========
+
+**rtla hwnoise** collects the periodic summary from the *osnoise* tracer
+running with *interrupts disabled*. By disabling interrupts, and the scheduling
+of threads as a consequence, only non-maskable interrupts and hardware-related
+noise is allowed.
+
+The tool also allows the configurations of the *osnoise* tracer and the
+collection of the tracer output.
+
+OPTIONS
+=======
+.. include:: common_osnoise_options.txt
+
+.. include:: common_top_options.txt
+
+.. include:: common_options.txt
+
+EXAMPLE
+=======
+In the example below, the **rtla hwnoise** tool is set to run on CPUs *1-7*
+on a system with 8 cores/16 threads with hyper-threading enabled.
+
+The tool is set to detect any noise higher than *one microsecond*,
+to run for *ten minutes*, displaying a summary of the report at the
+end of the session::
+
+  # rtla hwnoise -c 1-7 -T 1 -d 10m -q
+                                          Hardware-related Noise
+  duration:   0 00:10:00 | time is in us
+  CPU Period       Runtime        Noise  % CPU Aval   Max Noise   Max Single          HW          NMI
+    1 #599       599000000          138    99.99997           3            3           4           74
+    2 #599       599000000           85    99.99998           3            3           4           75
+    3 #599       599000000           86    99.99998           4            3           6           75
+    4 #599       599000000           81    99.99998           4            4           2           75
+    5 #599       599000000           85    99.99998           2            2           2           75
+    6 #599       599000000           76    99.99998           2            2           0           75
+    7 #599       599000000           77    99.99998           3            3           0           75
+
+
+The first column shows the *CPU*, and the second column shows how many
+*Periods* the tool ran during the session. The *Runtime* is the time
+the tool effectively runs on the CPU. The *Noise* column is the sum of
+all noise that the tool observed, and the *% CPU Aval* is the relation
+between the *Runtime* and *Noise*.
+
+The *Max Noise* column is the maximum hardware noise the tool detected in a
+single period, and the *Max Single* is the maximum single noise seen.
+
+The *HW* and *NMI* columns show the total number of *hardware* and *NMI* noise
+occurrence observed by the tool.
+
+For example, *CPU 3* ran *599* periods of *1 second Runtime*. The CPU received
+*86 us* of noise during the entire execution, leaving *99.99997 %* of CPU time
+for the application. In the worst single period, the CPU caused *4 us* of
+noise to the application, but it was certainly caused by more than one single
+noise, as the *Max Single* noise was of *3 us*. The CPU has *HW noise,* at a
+rate of *six occurrences*/*ten minutes*. The CPU also has *NMIs*, at a higher
+frequency: around *seven per second*.
+
+The tool should report *0* hardware-related noise in the ideal situation.
+For example, by disabling hyper-threading to remove the hardware noise,
+and disabling the TSC watchdog to remove the NMI (it is possible to identify
+this using tracing options of **rtla hwnoise**), it was possible to reach
+the ideal situation in the same hardware::
+
+  # rtla hwnoise -c 1-7 -T 1 -d 10m -q
+                                          Hardware-related Noise
+  duration:   0 00:10:00 | time is in us
+  CPU Period       Runtime        Noise  % CPU Aval   Max Noise   Max Single          HW          NMI
+    1 #599       599000000            0   100.00000           0            0           0            0
+    2 #599       599000000            0   100.00000           0            0           0            0
+    3 #599       599000000            0   100.00000           0            0           0            0
+    4 #599       599000000            0   100.00000           0            0           0            0
+    5 #599       599000000            0   100.00000           0            0           0            0
+    6 #599       599000000            0   100.00000           0            0           0            0
+    7 #599       599000000            0   100.00000           0            0           0            0
+
+SEE ALSO
+========
+
+**rtla-osnoise**\(1)
+
+`Osnoise tracer <https://docs.kernel.org/trace/osnoise-tracer.html>`__
+
+AUTHOR
+======
+Written by Daniel Bristot de Oliveira <bristot@kernel.org>
+
+.. include:: common_appendix.txt