When print_graph_entry() computes a function call entry event, it needs
to also check the next entry to guess if it matches the return event of
the current function entry.
In order to look at this next event, it needs to consume the current
entry before going ahead in the ring buffer.

However, if the current event that gets consumed is the last one in the
ring buffer head page, the ring_buffer may reuse the page for writers.
The consumed entry will then become invalid because of possible
racy overwriting.

Me must then handle this entry by making a copy of it.

The fix also applies on 2.6.30

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: stable@kernel.org
LKML-Reference: <4A6EEAEC.3050508@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

In case gcc does something funny with the stack frames, or the return
from function code, we would like to detect that.

An arch may implement passing of a variable that is unique to the
function and can be saved on entering a function and can be tested
when exiting the function. Usually the frame pointer can be used for
this purpose.

This patch also implements this for x86. Where it passes in the stack
frame of the parent function, and will test that frame on exit.

There was a case in x86_32 with optimize for size (-Os) where, for a
few functions, gcc would align the stack frame and place a copy of the
return address into it. The function graph tracer modified the copy and
not the actual return address. On return from the funtion, it did not go
to the tracer hook, but returned to the parent. This broke the function
graph tracer, because the return of the parent (where gcc did not do
this funky manipulation) returned to the location that the child function
was suppose to. This caused strange kernel crashes.

This test detected the problem and pointed out where the issue was.

This modifies the parameters of one of the functions that the arch
specific code calls, so it includes changes to arch code to accommodate
the new prototype.

Note, I notice that the parsic arch implements its own push_return_trace.
This is now a generic function and the ftrace_push_return_trace should be
used instead. This patch does not touch that code.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Kyle McMartin <kyle@mcmartin.ca>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

* 'tracing-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  function-graph: always initialize task ret_stack
  function-graph: move initialization of new tasks up in fork
  function-graph: add memory barriers for accessing task's ret_stack
  function-graph: enable the stack after initialization of other variables
  function-graph: only allocate init tasks if it was not already done

Manually fix trivial conflict in kernel/trace/ftrace.c

The function graph tracer checks if the task_struct has ret_stack defined
to know if it is OK or not to use it. The initialization is done for
all tasks by one process, but the idle tasks use the same initialization
used by new tasks.

If an interrupt happens on an idle task that just had the ret_stack
created, but before the rest of the initialization took place, then
we can corrupt the return address of the functions.

This patch moves the setting of the task_struct's ret_stack to after
the other variables have been initialized.

[ Impact: prevent kernel panic on idle task when starting function graph ]

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

graph time is the time that a function is executing another function.
Thus if function A calls B, if graph-time is set, then the time for
A includes B. This is the default behavior. But if graph-time is off,
then the time spent executing B is subtracted from A.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

If the function graph trace is enabled, the function profiler will
use it to take the timing of the functions.

 cat /debug/tracing/trace_stat/functions

  Function                               Hit    Time
  --------                               ---    ----
  mwait_idle                             127    183028.4 us
  schedule                                26    151997.7 us
  __schedule                              31    151975.1 us
  sys_wait4                                2    74080.53 us
  do_wait                                  2    74077.80 us
  sys_newlstat                           138    39929.16 us
  do_path_lookup                         179    39845.79 us
  vfs_lstat_fd                           138    39761.97 us
  user_path_at                           153    39469.58 us
  path_walk                              179    39435.76 us
  __link_path_walk                       189    39143.73 us
[...]

Note the times are skewed due to the function graph tracer not taking
into account schedules.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

This patch move the timestamp from happening in the arch specific
code into the general code. This allows for better control by the tracer
to time manipulation.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

With the added TRACE_EVENT macro, the events no longer appear in
the function graph tracer. This was because the function graph
did not know how to display the entries. The graph tracer was
only aware of its own entries and the printk entries.

By using the event call back feature, the graph tracer can now display
the events.

 # echo irq > /debug/tracing/set_event

Which can show:

 0)               |          handle_IRQ_event() {
 0)               |            /* irq_handler_entry: irq=48 handler=eth0 */
 0)               |            e1000_intr() {
 0)   0.926 us    |              __napi_schedule();
 0)   3.888 us    |            }
 0)               |            /* irq_handler_exit: irq=48 return=handled */
 0)   0.655 us    |            runqueue_is_locked();
 0)               |            __wake_up() {
 0)   0.831 us    |              _spin_lock_irqsave();

The irq entry and exit events show up as comments.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

Currently, the function graph tracer depends on the trace_printk
to record the depth. All the information is already there in the trace
to calculate function depth, with the exception of having the printk
be the first item. But as soon as a entry or exit is reached, then
we know the depth.

This patch changes the iter->private data from recording a per cpu
last_pid, to a structure that holds both the last_pid and the current
depth. This data is used to determine the function depth for the
printks.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

Impact: clean up

The prologue of the function graph entry, return and comments all
start out pretty much the same. Each of these duplicate code and
do so slightly differently.

This patch consolidates the printing of the pid, absolute time,
cpu and proc (and for entry, the interrupt).

Signed-off-by: Steven Rostedt <srostedt@redhat.com>