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, 146 insertions, 0 deletions

diff --git a/Documentation/driver-api/media/v4l2-device.rst b/Documentation/driver-api/media/v4l2-device.rst
new file mode 100644
index 000000000..7bd9c45f5
--- /dev/null
+++ b/Documentation/driver-api/media/v4l2-device.rst
@@ -0,0 +1,146 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+V4L2 device instance
+--------------------
+
+Each device instance is represented by a struct v4l2_device.
+Very simple devices can just allocate this struct, but most of the time you
+would embed this struct inside a larger struct.
+
+You must register the device instance by calling:
+
+	:c:func:`v4l2_device_register <v4l2_device_register>`
+	(dev, :c:type:`v4l2_dev <v4l2_device>`).
+
+Registration will initialize the :c:type:`v4l2_device` struct. If the
+dev->driver_data field is ``NULL``, it will be linked to
+:c:type:`v4l2_dev <v4l2_device>` argument.
+
+Drivers that want integration with the media device framework need to set
+dev->driver_data manually to point to the driver-specific device structure
+that embed the struct v4l2_device instance. This is achieved by a
+``dev_set_drvdata()`` call before registering the V4L2 device instance.
+They must also set the struct v4l2_device mdev field to point to a
+properly initialized and registered :c:type:`media_device` instance.
+
+If :c:type:`v4l2_dev <v4l2_device>`\ ->name is empty then it will be set to a
+value derived from dev (driver name followed by the bus_id, to be precise).
+If you set it up before  calling :c:func:`v4l2_device_register` then it will
+be untouched. If dev is ``NULL``, then you **must** setup
+:c:type:`v4l2_dev <v4l2_device>`\ ->name before calling
+:c:func:`v4l2_device_register`.
+
+You can use :c:func:`v4l2_device_set_name` to set the name based on a driver
+name and a driver-global atomic_t instance. This will generate names like
+``ivtv0``, ``ivtv1``, etc. If the name ends with a digit, then it will insert
+a dash: ``cx18-0``, ``cx18-1``, etc. This function returns the instance number.
+
+The first ``dev`` argument is normally the ``struct device`` pointer of a
+``pci_dev``, ``usb_interface`` or ``platform_device``. It is rare for dev to
+be ``NULL``, but it happens with ISA devices or when one device creates
+multiple PCI devices, thus making it impossible to associate
+:c:type:`v4l2_dev <v4l2_device>` with a particular parent.
+
+You can also supply a ``notify()`` callback that can be called by sub-devices
+to notify you of events. Whether you need to set this depends on the
+sub-device. Any notifications a sub-device supports must be defined in a header
+in ``include/media/subdevice.h``.
+
+V4L2 devices are unregistered by calling:
+
+	:c:func:`v4l2_device_unregister`
+	(:c:type:`v4l2_dev <v4l2_device>`).
+
+If the dev->driver_data field points to :c:type:`v4l2_dev <v4l2_device>`,
+it will be reset to ``NULL``. Unregistering will also automatically unregister
+all subdevs from the device.
+
+If you have a hotpluggable device (e.g. a USB device), then when a disconnect
+happens the parent device becomes invalid. Since :c:type:`v4l2_device` has a
+pointer to that parent device it has to be cleared as well to mark that the
+parent is gone. To do this call:
+
+	:c:func:`v4l2_device_disconnect`
+	(:c:type:`v4l2_dev <v4l2_device>`).
+
+This does *not* unregister the subdevs, so you still need to call the
+:c:func:`v4l2_device_unregister` function for that. If your driver is not
+hotpluggable, then there is no need to call :c:func:`v4l2_device_disconnect`.
+
+Sometimes you need to iterate over all devices registered by a specific
+driver. This is usually the case if multiple device drivers use the same
+hardware. E.g. the ivtvfb driver is a framebuffer driver that uses the ivtv
+hardware. The same is true for alsa drivers for example.
+
+You can iterate over all registered devices as follows:
+
+.. code-block:: c
+
+	static int callback(struct device *dev, void *p)
+	{
+		struct v4l2_device *v4l2_dev = dev_get_drvdata(dev);
+
+		/* test if this device was inited */
+		if (v4l2_dev == NULL)
+			return 0;
+		...
+		return 0;
+	}
+
+	int iterate(void *p)
+	{
+		struct device_driver *drv;
+		int err;
+
+		/* Find driver 'ivtv' on the PCI bus.
+		pci_bus_type is a global. For USB buses use usb_bus_type. */
+		drv = driver_find("ivtv", &pci_bus_type);
+		/* iterate over all ivtv device instances */
+		err = driver_for_each_device(drv, NULL, p, callback);
+		put_driver(drv);
+		return err;
+	}
+
+Sometimes you need to keep a running counter of the device instance. This is
+commonly used to map a device instance to an index of a module option array.
+
+The recommended approach is as follows:
+
+.. code-block:: c
+
+	static atomic_t drv_instance = ATOMIC_INIT(0);
+
+	static int drv_probe(struct pci_dev *pdev, const struct pci_device_id *pci_id)
+	{
+		...
+		state->instance = atomic_inc_return(&drv_instance) - 1;
+	}
+
+If you have multiple device nodes then it can be difficult to know when it is
+safe to unregister :c:type:`v4l2_device` for hotpluggable devices. For this
+purpose :c:type:`v4l2_device` has refcounting support. The refcount is
+increased whenever :c:func:`video_register_device` is called and it is
+decreased whenever that device node is released. When the refcount reaches
+zero, then the :c:type:`v4l2_device` release() callback is called. You can
+do your final cleanup there.
+
+If other device nodes (e.g. ALSA) are created, then you can increase and
+decrease the refcount manually as well by calling:
+
+	:c:func:`v4l2_device_get`
+	(:c:type:`v4l2_dev <v4l2_device>`).
+
+or:
+
+	:c:func:`v4l2_device_put`
+	(:c:type:`v4l2_dev <v4l2_device>`).
+
+Since the initial refcount is 1 you also need to call
+:c:func:`v4l2_device_put` in the ``disconnect()`` callback (for USB devices)
+or in the ``remove()`` callback (for e.g. PCI devices), otherwise the refcount
+will never reach 0.
+
+v4l2_device functions and data structures
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+.. kernel-doc:: include/media/v4l2-device.h