Merge tag 'trace-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing updates from Steven Rostedt:

 - The biggest news in that the tracing ring buffer can now time events
   that interrupted other ring buffer events.

   Before this change, if an interrupt came in while recording another
   event, and that interrupt also had an event, those events would all
   have the same time stamp as the event it interrupted.

   Now, with the new design, those events will have a unique time stamp
   and rightfully display the time for those events that were recorded
   while interrupting another event.

 - Bootconfig how has an "override" operator that lets the users have a
   default config, but then add options to override the default.

 - A fix was made to properly filter function graph tracing to the
   ftrace PIDs. This came in at the end of the -rc cycle, and needs to
   be backported.

 - Several clean ups, performance updates, and minor fixes as well.

* tag 'trace-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace: (39 commits)
  tracing: Add trace_array_init_printk() to initialize instance trace_printk() buffers
  kprobes: Fix compiler warning for !CONFIG_KPROBES_ON_FTRACE
  tracing: Use trace_sched_process_free() instead of exit() for pid tracing
  bootconfig: Fix to find the initargs correctly
  Documentation: bootconfig: Add bootconfig override operator
  tools/bootconfig: Add testcases for value override operator
  lib/bootconfig: Add override operator support
  kprobes: Remove show_registers() function prototype
  tracing/uprobe: Remove dead code in trace_uprobe_register()
  kprobes: Fix NULL pointer dereference at kprobe_ftrace_handler
  ftrace: Fix ftrace_trace_task return value
  tracepoint: Use __used attribute definitions from compiler_attributes.h
  tracepoint: Mark __tracepoint_string's __used
  trace : Have tracing buffer info use kvzalloc instead of kzalloc
  tracing: Remove outdated comment in stack handling
  ftrace: Do not let direct or IPMODIFY ftrace_ops be added to module and set trampolines
  ftrace: Setup correct FTRACE_FL_REGS flags for module
  tracing/hwlat: Honor the tracing_cpumask
  tracing/hwlat: Drop the duplicate assignment in start_kthread()
  tracing: Save one trace_event->type by using __TRACE_LAST_TYPE
  ...

1 files changed, 11 insertions, 0 deletions

diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
index d6b3b77a4129..a22024f9175e 100644
--- a/Documentation/admin-guide/bootconfig.rst
+++ b/Documentation/admin-guide/bootconfig.rst
@@ -71,6 +71,16 @@ For example,::
  foo = bar, baz
  foo = qux  # !ERROR! we can not re-define same key
 
+If you want to update the value, you must use the override operator
+``:=`` explicitly. For example::
+
+ foo = bar, baz
+ foo := qux
+
+then, the ``qux`` is assigned to ``foo`` key. This is useful for
+overriding the default value by adding (partial) custom bootconfigs
+without parsing the default bootconfig.
+
 If you want to append the value to existing key as an array member,
 you can use ``+=`` operator. For example::
 
@@ -84,6 +94,7 @@ For example, following config is NOT allowed.::
 
  foo = value1
  foo.bar = value2 # !ERROR! subkey "bar" and value "value1" can NOT co-exist
+ foo.bar := value2 # !ERROR! even with the override operator, this is NOT allowed.
 
 
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