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  1. 21 Dec, 2011 5 commits
    • Steven Rostedt's avatar
      ftrace: Allocate the mcount record pages as groups · a7900875
      Steven Rostedt authored 
      Allocate the mcount record pages as a group of pages as big
as can be allocated and waste no more than a single page.

Grouping the mcount pages as much as possible helps with cache
locality, as we do not need to redirect with descriptors as we
cross from page to page. It also allows us to do more with the
records later on (sort them with bigger benefits).
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      a7900875
    • Steven Rostedt's avatar
      ftrace: Remove usage of "freed" records · 32082309
      Steven Rostedt authored 
      Records that are added to the function trace table are
permanently there, except for modules. By separating out the
modules to their own pages that can be freed in one shot
we can remove the "freed" flag and simplify some of the record
management.

Another benefit of doing this is that we can also move the
records around; sort them.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      32082309
    • Steven Rostedt's avatar
      ftrace: Allow archs to modify code without stop machine · c88fd863
      Steven Rostedt authored 
      The stop machine method to modify all functions in the kernel
(some 20,000 of them) is the safest way to do so across all archs.
But some archs may not need this big hammer approach to modify code
on SMP machines, and can simply just update the code it needs.

Adding a weak function arch_ftrace_update_code() that now does the
stop machine, will also let any arch override this method.

If the arch needs to check the system and then decide if it can
avoid stop machine, it can still call ftrace_run_stop_machine() to
use the old method.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      c88fd863
    • Steven Rostedt's avatar
      ftrace: Do not function trace inlined functions · 45959ee7
      Steven Rostedt authored 
      When gcc inlines a function, it does not mark it with the mcount
prologue, which in turn means that inlined functions are not traced
by the function tracer. But if CONFIG_OPTIMIZE_INLINING is set, then
gcc is allowed not to inline a function that is marked inline.

Depending on the options and the compiler, a function may or may
not be traced by the function tracer, depending on whether gcc
decides to inline a function or not. This has caused several
problems in the pass becaues gcc is not always consistent with
what it decides to inline between different gcc versions.

Some places should not be traced (like paravirt native_* functions)
and these are mostly marked as inline. When gcc decides not to
inline the function, and if that function should not be traced, then
the ftrace function tracer will suddenly break when it use to work
fine. This becomes even harder to debug when different versions of
gcc will not inline that function, making the same kernel and config
work for some gcc versions and not work for others.

By making all functions marked inline to not be traced will remove
the ambiguity that gcc adds when it comes to tracing functions marked
inline. All gcc versions will be consistent with what functions are
traced and having volatile working code will be removed.

Note, only the inline macro when CONFIG_OPTIMIZE_INLINING is set needs
to have notrace added, as the attribute __always_inline will force
the function to be inlined and then not traced.
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      45959ee7
    • Jiri Olsa's avatar
      ftrace: Fix unregister ftrace_ops accounting · 30fb6aa7
      Jiri Olsa authored 
      Multiple users of the function tracer can register their functions
with the ftrace_ops structure. The accounting within ftrace will
update the counter on each function record that is being traced.
When the ftrace_ops filtering adds or removes functions, the
function records will be updated accordingly if the ftrace_ops is
still registered.

When a ftrace_ops is removed, the counter of the function records,
that the ftrace_ops traces, are decremented. When they reach zero
the functions that they represent are modified to stop calling the
mcount code.

When changes are made, the code is updated via stop_machine() with
a command passed to the function to tell it what to do. There is an
ENABLE and DISABLE command that tells the called function to enable
or disable the functions. But the ENABLE is really a misnomer as it
should just update the records, as records that have been enabled
and now have a count of zero should be disabled.

The DISABLE command is used to disable all functions regardless of
their counter values. This is the big off switch and is not the
complement of the ENABLE command.

To make matters worse, when a ftrace_ops is unregistered and there
is another ftrace_ops registered, neither the DISABLE nor the
ENABLE command are set when calling into the stop_machine() function
and the records will not be updated to match their counter. A command
is passed to that function that will update the mcount code to call
the registered callback directly if it is the only one left. This
means that the ftrace_ops that is still registered will have its callback
called by all functions that have been set for it as well as the ftrace_ops
that was just unregistered.

Here's a way to trigger this bug. Compile the kernel with
CONFIG_FUNCTION_PROFILER set and with CONFIG_FUNCTION_GRAPH not set:

 CONFIG_FUNCTION_PROFILER=y
 # CONFIG_FUNCTION_GRAPH is not set

This will force the function profiler to use the function tracer instead
of the function graph tracer.

  # cd /sys/kernel/debug/tracing
  # echo schedule > set_ftrace_filter
  # echo function > current_tracer
  # cat set_ftrace_filter
 schedule
  # cat trace
 # tracer: nop
 #
 # entries-in-buffer/entries-written: 692/68108025   #P:4
 #
 #                              _-----=> irqs-off
 #                             / _----=> need-resched
 #                            | / _---=> hardirq/softirq
 #                            || / _--=> preempt-depth
 #                            ||| /     delay
 #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
 #              | |       |   ||||       |         |
      kworker/0:2-909   [000] ....   531.235574: schedule <-worker_thread
           <idle>-0     [001] .N..   531.235575: schedule <-cpu_idle
      kworker/0:2-909   [000] ....   531.235597: schedule <-worker_thread
             sshd-2563  [001] ....   531.235647: schedule <-schedule_hrtimeout_range_clock

  # echo 1 > function_profile_enabled
  # echo 0 > function_porfile_enabled
  # cat set_ftrace_filter
 schedule
  # cat trace
 # tracer: function
 #
 # entries-in-buffer/entries-written: 159701/118821262   #P:4
 #
 #                              _-----=> irqs-off
 #                             / _----=> need-resched
 #                            | / _---=> hardirq/softirq
 #                            || / _--=> preempt-depth
 #                            ||| /     delay
 #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
 #              | |       |   ||||       |         |
           <idle>-0     [002] ...1   604.870655: local_touch_nmi <-cpu_idle
           <idle>-0     [002] d..1   604.870655: enter_idle <-cpu_idle
           <idle>-0     [002] d..1   604.870656: atomic_notifier_call_chain <-enter_idle
           <idle>-0     [002] d..1   604.870656: __atomic_notifier_call_chain <-atomic_notifier_call_chain

The same problem could have happened with the trace_probe_ops,
but they are modified with the set_frace_filter file which does the
update at closure of the file.

The simple solution is to change ENABLE to UPDATE and call it every
time an ftrace_ops is unregistered.

Link: http://lkml.kernel.org/r/1323105776-26961-3-git-send-email-jolsa@redhat.com

Cc: stable@vger.kernel.org # 3.0+
Signed-off-by: default avatarJiri Olsa <jolsa@redhat.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
      30fb6aa7
  3. 12 Dec, 2011 3 commits
  5. 06 Dec, 2011 14 commits
  7. 05 Dec, 2011 17 commits
  9. 02 Dec, 2011 1 commit
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