Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Don't destroy user event fields when removal fails

   User event fields are destroyed before the event is removed from
   visibility. But that can fail leaving the still visible event with no
   fields. Move the destroying of the fields to after the event is
   successfully removed from visibility.

 - Initialize function graph state is fork before calling
   copy_exec_state()

   For non-CLONE_VM forks, copy_exec_state() allocates a new
   task_exec_state. If that allocation fails, ftrace_graph_exit_task()
   will free the tasks ret_stack pointer. Since that pointer is still
   using the parent's ret_stack, it mistakenly frees the parent's
   pointer too.

   Call ftrace_graph_init() on the task first which will NULL out the
   new tasks's ret_stack and if the copy fails, it will not free
   anything.

 - Remove FGRAPH_MAX_INDEX

   The macro FGRAPH_MAX_INDEX was added but never used. Remove it.

 - Save ent_size in function graph printing of nested functions

   The function graph tracer needs to look at the next event to see if
   the next event is the return of the current function entry. If it is,
   it prints a single line:

	ktime_get();

   Otherwise it prints it like a nested function:

	tick_nohz_irq_exit() {
	    ktime_get();
	    kcpustat_irq_exit();
	}

   In order to look at the next event, it must save the current event so
   that it has the information to print from it. It saves the event in
   the iterator descriptor called "ent". What it doesn't save is the
   ent_size of the event which is now used to know if the function graph
   arguments are to be printed. The peek doesn't save the size so the
   size used happens to be that of the size of the last event that was
   seen.

   Save the entry event size in the iterator descriptor so that the
   correct size is used.

 - Fix several errors with freeing data in the histogram code

   The histogram code had a lot of leaked or or incorrect accounting
   when failures happen. Correct them.

 - Fix histogram regression of .percent and .graph modifiers

   Up until 6.3 histogram values could have "percent" or "graph"
   modifiers that changed how they were printed. But a change that added
   restricting histograms values from being strings, stack traces and
   other modifiers inadvertently prevented them from using the percent
   and graph modifiers, which were legal use cases for values.

   Put back the percent and graph modifiers.

 - Fix various typos in the comments

 - Set the trace_clock before initializing a histogram with clock
   argument

   The histogram API allows the user to specific which trace clock to
   use via a "clock=" string. The histogram is set up first before the
   clock is checked. If the passed in clock is not valid, it exits
   without fully fixing up the histogram leaving it on the list and a
   use-after-free can trigger.

   Update the clock argument first and if it fails then exit gracefully
   before the histogram trigger is placed on any lists.

 - Restore :mod: trailer after parsing in ftrace_set_clr_event

   The function ftrace_set_clr_event() modifies the parse string and
   needs to put it back to what was passed in. It searches for ":mod:"
   via a strsep() but fails to put back the first ':' in the string.

   Add back the ':' in the passed in string.

 - Take trace_array reference when opening a tracer options file

   The options files are dynamically created and some tracers add their
   own options. When a tracer adds their own list of options, the
   trace_array holding them has an array to hold the list of options for
   each tracer. This array increases in size via a krealloc(), and the
   new entry gets a newly allocated array to hold the options of the new
   tracer being added.

   The element in each entry of the tracer's option array holds a
   pointer back to the trace_array, a pointer to the tracer it is
   associated to, a pointer to the flags of the option.

   The issue is that these arrays are freed when the trace_array is
   freed when its instance it represents is removed from the instances
   directory. There's a race that an open of one of these options files
   can happen when the instance is being removed.

   Add a new helper function to be called by the open function of the
   options file to iterate all existing trace_arrays under a lock and
   find the one that has the given option element in one of it's tracer
   arrays. If found, then update the associated trace_array's reference
   counter to keep it from being freed. If not found, have the open call
   return -ENODEV.

 - Disable interrupts when acquiring the lock in rb_wake_up_waiters()

   The function rb_wake_up_waiters() assumes it will be called in
   interrupt context and does not disable irqs when taking
   cpu_buffer->reader_lock, which can be called in hard interrupt
   context. The issue is in PREEMPT_RT, this function is called in
   thread context leaving this lock open to a deadlock.

   Take the lock with interrupts disabled.

 - Use rcu_assign_pointer() for tmp_ops filter hash

   The tmp_ops used in update_ftrace_direct_mod() assigns its
   filter_hash field directly, but that field is annotated as __rcu and
   sparse complains. Assign it with rcu_assign_pointer()

 - Fix use-after-free in enable_trigger_private_data_free()

   The trace_event_call is accessed through the event_trigger_data's
   trace_event_file pointer to put the trace_event_call on freeing. The
   issue is that the trace_event_file data may have been freed already
   causing a use-after-free. Add a field to the event_trigger_data that
   points directly to the trace_event_call so that it can decrement its
   reference directly without needing to go through the
   trace_event_file.

 - Fix accounting of buffer data remote headers

   trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount
   the number of pages is needed for the asked for size as it doesn't
   take into account the meta data on each page. Add a helper function
   to do the calculation properly and use that in these functions.

 - Catch nr_page_va overflow in ring_buffer_desc sizing

   The number of pages per remote ring buffer is capped by
   ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to
   overflow that field would silently allocate a descriptor smaller than
   what was asked for.

 - Do not resize the subbuf order if any per_cpu buffer is disabled

   The mmapping of ring buffers disables resizing the subbuffers, but it
   is done per-cpu whereas the subbuf size change is done for all the
   per_cpu buffers under the buffer->mutex. It could change the size of
   some while the mapping is happening on others. Have the resize of the
   subbuf order check all the per_cpu buffers under the lock to see if
   any of them is disabled before starting and causing an inconsistency
   between buffers that are being mapped.

* tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits)
  ring-buffer: Check resize_disabled before publishing the new subbuf order
  tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing
  tracing/remotes: Account for ring buffer page header in size calculation
  tracing: Don't dereference trace_event_file in deferred trigger free
  ftrace: Use rcu_assign_pointer() for tmp_ops filter hash
  ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters()
  tracing: Take trace_array reference when opening a tracer options file
  tracing: Fix ring_buffer_read_page_size() kernel-doc
  tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event()
  tracing: Fix memory corruption from a "STACKTRACE" histogram key
  tracing: Fix memory corruption from the histogram stacktrace modifier
  tracing: Undo the registration when enabling the histogram trigger fails
  tracing: Take the reference before publishing the named histogram trigger
  tracing: Set the trace clock before registering the histogram trigger
  tracing: Fix typo "preceeded" in comment
  tracing: Fix typo "availabe" in comment
  tracing: Let histogram values keep the percent and graph modifiers
  tracing: Keep the entry count when the histogram stats allocation fails
  tracing: Free histogram the field rejected for a bad modifier
  tracing: Free histogram the var ref when its initialization fails
  ...

1 files changed, 167 insertions, 0 deletions

diff --git a/Documentation/livepatch/system-state.rst b/Documentation/livepatch/system-state.rst
new file mode 100644
index 000000000..7a3935fd8
--- /dev/null
+++ b/Documentation/livepatch/system-state.rst
@@ -0,0 +1,167 @@
+====================
+System State Changes
+====================
+
+Some users are really reluctant to reboot a system. This brings the need
+to provide more livepatches and maintain some compatibility between them.
+
+Maintaining more livepatches is much easier with cumulative livepatches.
+Each new livepatch completely replaces any older one. It can keep,
+add, and even remove fixes. And it is typically safe to replace any version
+of the livepatch with any other one thanks to the atomic replace feature.
+
+The problems might come with shadow variables and callbacks. They might
+change the system behavior or state so that it is no longer safe to
+go back and use an older livepatch or the original kernel code. Also
+any new livepatch must be able to detect what changes have already been
+done by the already installed livepatches.
+
+This is where the livepatch system state tracking gets useful. It
+allows to:
+
+  - store data needed to manipulate and restore the system state
+
+  - define compatibility between livepatches using a change id
+    and version
+
+
+1. Livepatch system state API
+=============================
+
+The state of the system might get modified either by several livepatch callbacks
+or by the newly used code. Also it must be possible to find changes done by
+already installed livepatches.
+
+Each modified state is described by struct klp_state, see
+include/linux/livepatch.h.
+
+Each livepatch defines an array of struct klp_states. They mention
+all states that the livepatch modifies.
+
+The livepatch author must define the following two fields for each
+struct klp_state:
+
+  - *id*
+
+    - Non-zero number used to identify the affected system state.
+
+  - *version*
+
+    - Number describing the variant of the system state change that
+      is supported by the given livepatch.
+
+The state can be manipulated using two functions:
+
+  - klp_get_state()
+
+    - Get struct klp_state associated with the given livepatch
+      and state id.
+
+  - klp_get_prev_state()
+
+    - Get struct klp_state associated with the given feature id and
+      already installed livepatches.
+
+2. Livepatch compatibility
+==========================
+
+The system state version is used to prevent loading incompatible livepatches.
+The check is done when the livepatch is enabled. The rules are:
+
+  - Any completely new system state modification is allowed.
+
+  - System state modifications with the same or higher version are allowed
+    for already modified system states.
+
+  - Cumulative livepatches must handle all system state modifications from
+    already installed livepatches.
+
+  - Non-cumulative livepatches are allowed to touch already modified
+    system states.
+
+3. Supported scenarios
+======================
+
+Livepatches have their life-cycle and the same is true for the system
+state changes. Every compatible livepatch has to support the following
+scenarios:
+
+  - Modify the system state when the livepatch gets enabled and the state
+    has not been already modified by a livepatches that are being
+    replaced.
+
+  - Take over or update the system state modification when is has already
+    been done by a livepatch that is being replaced.
+
+  - Restore the original state when the livepatch is disabled.
+
+  - Restore the previous state when the transition is reverted.
+    It might be the original system state or the state modification
+    done by livepatches that were being replaced.
+
+  - Remove any already made changes when error occurs and the livepatch
+    cannot get enabled.
+
+4. Expected usage
+=================
+
+System states are usually modified by livepatch callbacks. The expected
+role of each callback is as follows:
+
+*pre_patch()*
+
+  - Allocate *state->data* when necessary. The allocation might fail
+    and *pre_patch()* is the only callback that could stop loading
+    of the livepatch. The allocation is not needed when the data
+    are already provided by previously installed livepatches.
+
+  - Do any other preparatory action that is needed by
+    the new code even before the transition gets finished.
+    For example, initialize *state->data*.
+
+    The system state itself is typically modified in *post_patch()*
+    when the entire system is able to handle it.
+
+  - Clean up its own mess in case of error. It might be done by a custom
+    code or by calling *post_unpatch()* explicitly.
+
+*post_patch()*
+
+  - Copy *state->data* from the previous livepatch when they are
+    compatible.
+
+  - Do the actual system state modification. Eventually allow
+    the new code to use it.
+
+  - Make sure that *state->data* has all necessary information.
+
+  - Free *state->data* from replaces livepatches when they are
+    not longer needed.
+
+*pre_unpatch()*
+
+  - Prevent the code, added by the livepatch, relying on the system
+    state change.
+
+  - Revert the system state modification..
+
+*post_unpatch()*
+
+  - Distinguish transition reverse and livepatch disabling by
+    checking *klp_get_prev_state()*.
+
+  - In case of transition reverse, restore the previous system
+    state. It might mean doing nothing.
+
+  - Remove any not longer needed setting or data.
+
+.. note::
+
+   *pre_unpatch()* typically does symmetric operations to *post_patch()*.
+   Except that it is called only when the livepatch is being disabled.
+   Therefore it does not need to care about any previously installed
+   livepatch.
+
+   *post_unpatch()* typically does symmetric operations to *pre_patch()*.
+   It might be called also during the transition reverse. Therefore it
+   has to handle the state of the previously installed livepatches.