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, 320 insertions, 0 deletions

diff --git a/Documentation/driver-api/device_link.rst b/Documentation/driver-api/device_link.rst
new file mode 100644
index 000000000..ee913ae16
--- /dev/null
+++ b/Documentation/driver-api/device_link.rst
@@ -0,0 +1,320 @@
+.. _device_link:
+
+============
+Device links
+============
+
+By default, the driver core only enforces dependencies between devices
+that are borne out of a parent/child relationship within the device
+hierarchy: When suspending, resuming or shutting down the system, devices
+are ordered based on this relationship, i.e. children are always suspended
+before their parent, and the parent is always resumed before its children.
+
+Sometimes there is a need to represent device dependencies beyond the
+mere parent/child relationship, e.g. between siblings, and have the
+driver core automatically take care of them.
+
+Secondly, the driver core by default does not enforce any driver presence
+dependencies, i.e. that one device must be bound to a driver before
+another one can probe or function correctly.
+
+Often these two dependency types come together, so a device depends on
+another one both with regards to driver presence *and* with regards to
+suspend/resume and shutdown ordering.
+
+Device links allow representation of such dependencies in the driver core.
+
+In its standard or *managed* form, a device link combines *both* dependency
+types:  It guarantees correct suspend/resume and shutdown ordering between a
+"supplier" device and its "consumer" devices, and it guarantees driver
+presence on the supplier.  The consumer devices are not probed before the
+supplier is bound to a driver, and they're unbound before the supplier
+is unbound.
+
+When driver presence on the supplier is irrelevant and only correct
+suspend/resume and shutdown ordering is needed, the device link may
+simply be set up with the ``DL_FLAG_STATELESS`` flag.  In other words,
+enforcing driver presence on the supplier is optional.
+
+Another optional feature is runtime PM integration:  By setting the
+``DL_FLAG_PM_RUNTIME`` flag on addition of the device link, the PM core
+is instructed to runtime resume the supplier and keep it active
+whenever and for as long as the consumer is runtime resumed.
+
+Usage
+=====
+
+The earliest point in time when device links can be added is after
+:c:func:`device_add()` has been called for the supplier and
+:c:func:`device_initialize()` has been called for the consumer.
+
+It is legal to add them later, but care must be taken that the system
+remains in a consistent state:  E.g. a device link cannot be added in
+the midst of a suspend/resume transition, so either commencement of
+such a transition needs to be prevented with :c:func:`lock_system_sleep()`,
+or the device link needs to be added from a function which is guaranteed
+not to run in parallel to a suspend/resume transition, such as from a
+device ``->probe`` callback or a boot-time PCI quirk.
+
+Another example for an inconsistent state would be a device link that
+represents a driver presence dependency, yet is added from the consumer's
+``->probe`` callback while the supplier hasn't started to probe yet:  Had the
+driver core known about the device link earlier, it wouldn't have probed the
+consumer in the first place.  The onus is thus on the consumer to check
+presence of the supplier after adding the link, and defer probing on
+non-presence.  [Note that it is valid to create a link from the consumer's
+``->probe`` callback while the supplier is still probing, but the consumer must
+know that the supplier is functional already at the link creation time (that is
+the case, for instance, if the consumer has just acquired some resources that
+would not have been available had the supplier not been functional then).]
+
+If a device link with ``DL_FLAG_STATELESS`` set (i.e. a stateless device link)
+is added in the ``->probe`` callback of the supplier or consumer driver, it is
+typically deleted in its ``->remove`` callback for symmetry.  That way, if the
+driver is compiled as a module, the device link is added on module load and
+orderly deleted on unload.  The same restrictions that apply to device link
+addition (e.g. exclusion of a parallel suspend/resume transition) apply equally
+to deletion.  Device links managed by the driver core are deleted automatically
+by it.
+
+Several flags may be specified on device link addition, two of which
+have already been mentioned above:  ``DL_FLAG_STATELESS`` to express that no
+driver presence dependency is needed (but only correct suspend/resume and
+shutdown ordering) and ``DL_FLAG_PM_RUNTIME`` to express that runtime PM
+integration is desired.
+
+Two other flags are specifically targeted at use cases where the device
+link is added from the consumer's ``->probe`` callback:  ``DL_FLAG_RPM_ACTIVE``
+can be specified to runtime resume the supplier and prevent it from suspending
+before the consumer is runtime suspended.  ``DL_FLAG_AUTOREMOVE_CONSUMER``
+causes the device link to be automatically purged when the consumer fails to
+probe or later unbinds.
+
+Similarly, when the device link is added from supplier's ``->probe`` callback,
+``DL_FLAG_AUTOREMOVE_SUPPLIER`` causes the device link to be automatically
+purged when the supplier fails to probe or later unbinds.
+
+If neither ``DL_FLAG_AUTOREMOVE_CONSUMER`` nor ``DL_FLAG_AUTOREMOVE_SUPPLIER``
+is set, ``DL_FLAG_AUTOPROBE_CONSUMER`` can be used to request the driver core
+to probe for a driver for the consumer driver on the link automatically after
+a driver has been bound to the supplier device.
+
+Note, however, that any combinations of ``DL_FLAG_AUTOREMOVE_CONSUMER``,
+``DL_FLAG_AUTOREMOVE_SUPPLIER`` or ``DL_FLAG_AUTOPROBE_CONSUMER`` with
+``DL_FLAG_STATELESS`` are invalid and cannot be used.
+
+Limitations
+===========
+
+Driver authors should be aware that a driver presence dependency for managed
+device links (i.e. when ``DL_FLAG_STATELESS`` is not specified on link addition)
+may cause probing of the consumer to be deferred indefinitely.  This can become
+a problem if the consumer is required to probe before a certain initcall level
+is reached.  Worse, if the supplier driver is blacklisted or missing, the
+consumer will never be probed.
+
+Moreover, managed device links cannot be deleted directly.  They are deleted
+by the driver core when they are not necessary any more in accordance with the
+``DL_FLAG_AUTOREMOVE_CONSUMER`` and ``DL_FLAG_AUTOREMOVE_SUPPLIER`` flags.
+However, stateless device links (i.e. device links with ``DL_FLAG_STATELESS``
+set) are expected to be removed by whoever called :c:func:`device_link_add()`
+to add them with the help of either :c:func:`device_link_del()` or
+:c:func:`device_link_remove()`.
+
+Passing ``DL_FLAG_RPM_ACTIVE`` along with ``DL_FLAG_STATELESS`` to
+:c:func:`device_link_add()` may cause the PM-runtime usage counter of the
+supplier device to remain nonzero after a subsequent invocation of either
+:c:func:`device_link_del()` or :c:func:`device_link_remove()` to remove the
+device link returned by it.  This happens if :c:func:`device_link_add()` is
+called twice in a row for the same consumer-supplier pair without removing the
+link between these calls, in which case allowing the PM-runtime usage counter
+of the supplier to drop on an attempt to remove the link may cause it to be
+suspended while the consumer is still PM-runtime-active and that has to be
+avoided.  [To work around this limitation it is sufficient to let the consumer
+runtime suspend at least once, or call :c:func:`pm_runtime_set_suspended()` for
+it with PM-runtime disabled, between the :c:func:`device_link_add()` and
+:c:func:`device_link_del()` or :c:func:`device_link_remove()` calls.]
+
+Sometimes drivers depend on optional resources.  They are able to operate
+in a degraded mode (reduced feature set or performance) when those resources
+are not present.  An example is an SPI controller that can use a DMA engine
+or work in PIO mode.  The controller can determine presence of the optional
+resources at probe time but on non-presence there is no way to know whether
+they will become available in the near future (due to a supplier driver
+probing) or never.  Consequently it cannot be determined whether to defer
+probing or not.  It would be possible to notify drivers when optional
+resources become available after probing, but it would come at a high cost
+for drivers as switching between modes of operation at runtime based on the
+availability of such resources would be much more complex than a mechanism
+based on probe deferral.  In any case optional resources are beyond the
+scope of device links.
+
+Examples
+========
+
+* An MMU device exists alongside a busmaster device, both are in the same
+  power domain.  The MMU implements DMA address translation for the busmaster
+  device and shall be runtime resumed and kept active whenever and as long
+  as the busmaster device is active.  The busmaster device's driver shall
+  not bind before the MMU is bound.  To achieve this, a device link with
+  runtime PM integration is added from the busmaster device (consumer)
+  to the MMU device (supplier).  The effect with regards to runtime PM
+  is the same as if the MMU was the parent of the master device.
+
+  The fact that both devices share the same power domain would normally
+  suggest usage of a struct dev_pm_domain or struct generic_pm_domain,
+  however these are not independent devices that happen to share a power
+  switch, but rather the MMU device serves the busmaster device and is
+  useless without it.  A device link creates a synthetic hierarchical
+  relationship between the devices and is thus more apt.
+
+* A Thunderbolt host controller comprises a number of PCIe hotplug ports
+  and an NHI device to manage the PCIe switch.  On resume from system sleep,
+  the NHI device needs to re-establish PCI tunnels to attached devices
+  before the hotplug ports can resume.  If the hotplug ports were children
+  of the NHI, this resume order would automatically be enforced by the
+  PM core, but unfortunately they're aunts.  The solution is to add
+  device links from the hotplug ports (consumers) to the NHI device
+  (supplier).  A driver presence dependency is not necessary for this
+  use case.
+
+* Discrete GPUs in hybrid graphics laptops often feature an HDA controller
+  for HDMI/DP audio.  In the device hierarchy the HDA controller is a sibling
+  of the VGA device, yet both share the same power domain and the HDA
+  controller is only ever needed when an HDMI/DP display is attached to the
+  VGA device.  A device link from the HDA controller (consumer) to the
+  VGA device (supplier) aptly represents this relationship.
+
+* ACPI allows definition of a device start order by way of _DEP objects.
+  A classical example is when ACPI power management methods on one device
+  are implemented in terms of I\ :sup:`2`\ C accesses and require a specific
+  I\ :sup:`2`\ C controller to be present and functional for the power
+  management of the device in question to work.
+
+* In some SoCs a functional dependency exists from display, video codec and
+  video processing IP cores on transparent memory access IP cores that handle
+  burst access and compression/decompression.
+
+Alternatives
+============
+
+* A struct dev_pm_domain can be used to override the bus,
+  class or device type callbacks.  It is intended for devices sharing
+  a single on/off switch, however it does not guarantee a specific
+  suspend/resume ordering, this needs to be implemented separately.
+  It also does not by itself track the runtime PM status of the involved
+  devices and turn off the power switch only when all of them are runtime
+  suspended.  Furthermore it cannot be used to enforce a specific shutdown
+  ordering or a driver presence dependency.
+
+* A struct generic_pm_domain is a lot more heavyweight than a
+  device link and does not allow for shutdown ordering or driver presence
+  dependencies.  It also cannot be used on ACPI systems.
+
+Implementation
+==============
+
+The device hierarchy, which -- as the name implies -- is a tree,
+becomes a directed acyclic graph once device links are added.
+
+Ordering of these devices during suspend/resume is determined by the
+dpm_list.  During shutdown it is determined by the devices_kset.  With
+no device links present, the two lists are a flattened, one-dimensional
+representations of the device tree such that a device is placed behind
+all its ancestors.  That is achieved by traversing the ACPI namespace
+or OpenFirmware device tree top-down and appending devices to the lists
+as they are discovered.
+
+Once device links are added, the lists need to satisfy the additional
+constraint that a device is placed behind all its suppliers, recursively.
+To ensure this, upon addition of the device link the consumer and the
+entire sub-graph below it (all children and consumers of the consumer)
+are moved to the end of the list.  (Call to :c:func:`device_reorder_to_tail()`
+from :c:func:`device_link_add()`.)
+
+To prevent introduction of dependency loops into the graph, it is
+verified upon device link addition that the supplier is not dependent
+on the consumer or any children or consumers of the consumer.
+(Call to :c:func:`device_is_dependent()` from :c:func:`device_link_add()`.)
+If that constraint is violated, :c:func:`device_link_add()` will return
+``NULL`` and a ``WARNING`` will be logged.
+
+Notably this also prevents the addition of a device link from a parent
+device to a child.  However the converse is allowed, i.e. a device link
+from a child to a parent.  Since the driver core already guarantees
+correct suspend/resume and shutdown ordering between parent and child,
+such a device link only makes sense if a driver presence dependency is
+needed on top of that.  In this case driver authors should weigh
+carefully if a device link is at all the right tool for the purpose.
+A more suitable approach might be to simply use deferred probing or
+add a device flag causing the parent driver to be probed before the
+child one.
+
+State machine
+=============
+
+.. kernel-doc:: include/linux/device.h
+   :functions: device_link_state
+
+::
+
+                 .=============================.
+                 |                             |
+                 v                             |
+ DORMANT <=> AVAILABLE <=> CONSUMER_PROBE => ACTIVE
+    ^                                          |
+    |                                          |
+    '============ SUPPLIER_UNBIND <============'
+
+* The initial state of a device link is automatically determined by
+  :c:func:`device_link_add()` based on the driver presence on the supplier
+  and consumer.  If the link is created before any devices are probed, it
+  is set to ``DL_STATE_DORMANT``.
+
+* When a supplier device is bound to a driver, links to its consumers
+  progress to ``DL_STATE_AVAILABLE``.
+  (Call to :c:func:`device_links_driver_bound()` from
+  :c:func:`driver_bound()`.)
+
+* Before a consumer device is probed, presence of supplier drivers is
+  verified by checking the consumer device is not in the wait_for_suppliers
+  list and by checking that links to suppliers are in ``DL_STATE_AVAILABLE``
+  state.  The state of the links is updated to ``DL_STATE_CONSUMER_PROBE``.
+  (Call to :c:func:`device_links_check_suppliers()` from
+  :c:func:`really_probe()`.)
+  This prevents the supplier from unbinding.
+  (Call to :c:func:`wait_for_device_probe()` from
+  :c:func:`device_links_unbind_consumers()`.)
+
+* If the probe fails, links to suppliers revert back to ``DL_STATE_AVAILABLE``.
+  (Call to :c:func:`device_links_no_driver()` from :c:func:`really_probe()`.)
+
+* If the probe succeeds, links to suppliers progress to ``DL_STATE_ACTIVE``.
+  (Call to :c:func:`device_links_driver_bound()` from :c:func:`driver_bound()`.)
+
+* When the consumer's driver is later on removed, links to suppliers revert
+  back to ``DL_STATE_AVAILABLE``.
+  (Call to :c:func:`__device_links_no_driver()` from
+  :c:func:`device_links_driver_cleanup()`, which in turn is called from
+  :c:func:`__device_release_driver()`.)
+
+* Before a supplier's driver is removed, links to consumers that are not
+  bound to a driver are updated to ``DL_STATE_SUPPLIER_UNBIND``.
+  (Call to :c:func:`device_links_busy()` from
+  :c:func:`__device_release_driver()`.)
+  This prevents the consumers from binding.
+  (Call to :c:func:`device_links_check_suppliers()` from
+  :c:func:`really_probe()`.)
+  Consumers that are bound are freed from their driver; consumers that are
+  probing are waited for until they are done.
+  (Call to :c:func:`device_links_unbind_consumers()` from
+  :c:func:`__device_release_driver()`.)
+  Once all links to consumers are in ``DL_STATE_SUPPLIER_UNBIND`` state,
+  the supplier driver is released and the links revert to ``DL_STATE_DORMANT``.
+  (Call to :c:func:`device_links_driver_cleanup()` from
+  :c:func:`__device_release_driver()`.)
+
+API
+===
+
+See device_link_add(), device_link_del() and device_link_remove().