Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

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.