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/tools/rtla/rtla-timerlat-top.rst b/Documentation/tools/rtla/rtla-timerlat-top.rst
new file mode 100644
index 000000000..05959f1a4
--- /dev/null
+++ b/Documentation/tools/rtla/rtla-timerlat-top.rst
@@ -0,0 +1,136 @@
+.. |tool| replace:: timerlat top
+
+====================
+rtla-timerlat-top
+====================
+-------------------------------------------
+Measures the operating system timer latency
+-------------------------------------------
+
+:Manual section: 1
+
+SYNOPSIS
+========
+**rtla timerlat top** [*OPTIONS*] ...
+
+DESCRIPTION
+===========
+
+.. include:: common_timerlat_description.txt
+
+The **rtla timerlat top** displays a summary of the periodic output
+from the *timerlat* tracer. It also provides information for each
+operating system noise via the **osnoise:** tracepoints that can be
+seen with the option **-T**.
+
+OPTIONS
+=======
+
+.. include:: common_timerlat_options.txt
+
+.. include:: common_top_options.txt
+
+.. include:: common_options.txt
+
+.. include:: common_timerlat_aa.txt
+
+**--aa-only** *us*
+
+        Set stop tracing conditions and run without collecting and displaying statistics.
+        Print the auto-analysis if the system hits the stop tracing condition. This option
+        is useful to reduce rtla timerlat CPU, enabling the debug without the overhead of
+        collecting the statistics.
+
+EXAMPLE
+=======
+
+In the example below, the timerlat tracer is dispatched in cpus *1-23* in the
+automatic trace mode, instructing the tracer to stop if a *40 us* latency or
+higher is found::
+
+  # timerlat -a 40 -c 1-23 -q
+                                     Timer Latency
+    0 00:00:12   |          IRQ Timer Latency (us)        |         Thread Timer Latency (us)
+  CPU COUNT      |      cur       min       avg       max |      cur       min       avg       max
+    1 #12322     |        0         0         1        15 |       10         3         9        31
+    2 #12322     |        3         0         1        12 |       10         3         9        23
+    3 #12322     |        1         0         1        21 |        8         2         8        34
+    4 #12322     |        1         0         1        17 |       10         2        11        33
+    5 #12322     |        0         0         1        12 |        8         3         8        25
+    6 #12322     |        1         0         1        14 |       16         3        11        35
+    7 #12322     |        0         0         1        14 |        9         2         8        29
+    8 #12322     |        1         0         1        22 |        9         3         9        34
+    9 #12322     |        0         0         1        14 |        8         2         8        24
+   10 #12322     |        1         0         0        12 |        9         3         8        24
+   11 #12322     |        0         0         0        15 |        6         2         7        29
+   12 #12321     |        1         0         0        13 |        5         3         8        23
+   13 #12319     |        0         0         1        14 |        9         3         9        26
+   14 #12321     |        1         0         0        13 |        6         2         8        24
+   15 #12321     |        1         0         1        15 |       12         3        11        27
+   16 #12318     |        0         0         1        13 |        7         3        10        24
+   17 #12319     |        0         0         1        13 |       11         3         9        25
+   18 #12318     |        0         0         0        12 |        8         2         8        20
+   19 #12319     |        0         0         1        18 |       10         2         9        28
+   20 #12317     |        0         0         0        20 |        9         3         8        34
+   21 #12318     |        0         0         0        13 |        8         3         8        28
+   22 #12319     |        0         0         1        11 |        8         3        10        22
+   23 #12320     |       28         0         1        28 |       41         3        11        41
+  rtla timerlat hit stop tracing
+  ## CPU 23 hit stop tracing, analyzing it ##
+  IRQ handler delay:                                        27.49 us (65.52 %)
+  IRQ latency:                                              28.13 us
+  Timerlat IRQ duration:                                     9.59 us (22.85 %)
+  Blocking thread:                                           3.79 us (9.03 %)
+                         objtool:49256                       3.79 us
+    Blocking thread stacktrace
+                -> timerlat_irq
+                -> __hrtimer_run_queues
+                -> hrtimer_interrupt
+                -> __sysvec_apic_timer_interrupt
+                -> sysvec_apic_timer_interrupt
+                -> asm_sysvec_apic_timer_interrupt
+                -> _raw_spin_unlock_irqrestore
+                -> cgroup_rstat_flush_locked
+                -> cgroup_rstat_flush_irqsafe
+                -> mem_cgroup_flush_stats
+                -> mem_cgroup_wb_stats
+                -> balance_dirty_pages
+                -> balance_dirty_pages_ratelimited_flags
+                -> btrfs_buffered_write
+                -> btrfs_do_write_iter
+                -> vfs_write
+                -> __x64_sys_pwrite64
+                -> do_syscall_64
+                -> entry_SYSCALL_64_after_hwframe
+  ------------------------------------------------------------------------
+    Thread latency:                                          41.96 us (100%)
+
+  The system has exit from idle latency!
+    Max timerlat IRQ latency from idle: 17.48 us in cpu 4
+  Saving trace to timerlat_trace.txt
+
+In this case, the major factor was the delay suffered by the *IRQ handler*
+that handles **timerlat** wakeup: *65.52%*. This can be caused by the
+current thread masking interrupts, which can be seen in the blocking
+thread stacktrace: the current thread (*objtool:49256*) disabled interrupts
+via *raw spin lock* operations inside mem cgroup, while doing write
+syscall in a btrfs file system.
+
+The raw trace is saved in the **timerlat_trace.txt** file for further analysis.
+
+Note that **rtla timerlat** was dispatched without changing *timerlat* tracer
+threads' priority. That is generally not needed because these threads have
+priority *FIFO:95* by default, which is a common priority used by real-time
+kernel developers to analyze scheduling delays.
+
+SEE ALSO
+--------
+**rtla-timerlat**\(1), **rtla-timerlat-hist**\(1)
+
+`Timerlat tracer <https://docs.kernel.org/trace/timerlat-tracer.html>`__
+
+AUTHOR
+------
+Written by Daniel Bristot de Oliveira <bristot@kernel.org>
+
+.. include:: common_appendix.txt