Merge tag 'trace-v7.0-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull tracing fixes from Steven Rostedt:

- Fix possible dereference of uninitialized pointer

When validating the persistent ring buffer on boot up, if the first
validation fails, a reference to "head_page" is performed in the
error path, but it skips over the initialization of that variable.
Move the initialization before the first validation check.

- Fix use of event length in validation of persistent ring buffer

On boot up, the persistent ring buffer is checked to see if it is
valid by several methods. One being to walk all the events in the
memory location to make sure they are all valid. The length of the
event is used to move to the next event. This length is determined by
the data in the buffer. If that length is corrupted, it could
possibly make the next event to check located at a bad memory
location.

Validate the length field of the event when doing the event walk.

- Fix function graph on archs that do not support use of ftrace_ops

When an architecture defines HAVE_DYNAMIC_FTRACE_WITH_ARGS, it means
that its function graph tracer uses the ftrace_ops of the function
tracer to call its callbacks. This allows a single registered
callback to be called directly instead of checking the callback's
meta data's hash entries against the function being traced.

For architectures that do not support this feature, it must always
call the loop function that tests each registered callback (even if
there's only one). The loop function tests each callback's meta data
against its hash of functions and will call its callback if the
function being traced is in its hash map.

The issue was that there was no check against this and the direct
function was being called even if the architecture didn't support it.
This meant that if function tracing was enabled at the same time as a
callback was registered with the function graph tracer, its callback
would be called for every function that the function tracer also
traced, even if the callback's meta data only wanted to be called
back for a small subset of functions.

Prevent the direct calling for those architectures that do not
support it.

- Fix references to trace_event_file for hist files

The hist files used event_file_data() to get a reference to the
associated trace_event_file the histogram was attached to. This would
return a pointer even if the trace_event_file is about to be freed
(via RCU). Instead it should use the event_file_file() helper that
returns NULL if the trace_event_file is marked to be freed so that no
new references are added to it.

- Wake up hist poll readers when an event is being freed

When polling on a hist file, the task is only awoken when a hist
trigger is triggered. This means that if an event is being freed
while there's a task waiting on its hist file, it will need to wait
until the hist trigger occurs to wake it up and allow the freeing to
happen. Note, the event will not be completely freed until all
references are removed, and a hist poller keeps a reference. But it
should still be woken when the event is being freed.

* tag 'trace-v7.0-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
tracing: Wake up poll waiters for hist files when removing an event
tracing: Fix checking of freed trace_event_file for hist files
fgraph: Do not call handlers direct when not using ftrace_ops
tracing: ring-buffer: Fix to check event length before using
ring-buffer: Fix possible dereference of uninitialized pointer