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, 287 insertions, 0 deletions

diff --git a/Documentation/gpu/vkms.rst b/Documentation/gpu/vkms.rst
new file mode 100644
index 000000000..1e79e62a6
--- /dev/null
+++ b/Documentation/gpu/vkms.rst
@@ -0,0 +1,287 @@
+.. _vkms:
+
+==========================================
+ drm/vkms Virtual Kernel Modesetting
+==========================================
+
+.. kernel-doc:: drivers/gpu/drm/vkms/vkms_drv.c
+   :doc: vkms (Virtual Kernel Modesetting)
+
+Setup
+=====
+
+The VKMS driver can be setup with the following steps:
+
+To check if VKMS is loaded, run::
+
+  lsmod | grep vkms
+
+This should list the VKMS driver. If no output is obtained, then
+you need to enable and/or load the VKMS driver.
+Ensure that the VKMS driver has been set as a loadable module in your
+kernel config file. Do::
+
+  make nconfig
+
+  Go to `Device Drivers> Graphics support`
+
+  Enable `Virtual KMS (EXPERIMENTAL)`
+
+Compile and build the kernel for the changes to get reflected.
+Now, to load the driver, use::
+
+  sudo modprobe vkms
+
+On running the lsmod command now, the VKMS driver will appear listed.
+You can also observe the driver being loaded in the dmesg logs.
+
+The VKMS driver has optional features to simulate different kinds of hardware,
+which are exposed as module options. You can use the `modinfo` command
+to see the module options for vkms::
+
+  modinfo vkms
+
+Module options are helpful when testing, and enabling modules
+can be done while loading vkms. For example, to load vkms with cursor enabled,
+use::
+
+  sudo modprobe vkms enable_cursor=1
+
+To disable the driver, use ::
+
+  sudo modprobe -r vkms
+
+Configuring With Configfs
+=========================
+
+It is possible to create and configure multiple VKMS instances via configfs.
+
+Start by mounting configfs and loading VKMS::
+
+  sudo mount -t configfs none /config
+  sudo modprobe vkms
+
+Once VKMS is loaded, ``/config/vkms`` is created automatically. Each directory
+under ``/config/vkms`` represents a VKMS instance, create a new one::
+
+  sudo mkdir /config/vkms/my-vkms
+
+By default, the instance is disabled::
+
+  cat /config/vkms/my-vkms/enabled
+  0
+
+And directories are created for each configurable item of the display pipeline::
+
+  tree /config/vkms/my-vkms
+  ├── connectors
+  ├── crtcs
+  ├── enabled
+  ├── encoders
+  └── planes
+
+To add items to the display pipeline, create one or more directories under the
+available paths.
+
+Start by creating one or more planes::
+
+  sudo mkdir /config/vkms/my-vkms/planes/plane0
+
+Planes have 1 configurable attribute:
+
+- type: Plane type: 0 overlay, 1 primary, 2 cursor (same values as those
+  exposed by the "type" property of a plane)
+
+Continue by creating one or more CRTCs::
+
+  sudo mkdir /config/vkms/my-vkms/crtcs/crtc0
+
+CRTCs have 1 configurable attribute:
+
+- writeback: Enable or disable writeback connector support by writing 1 or 0
+
+Next, create one or more encoders::
+
+  sudo mkdir /config/vkms/my-vkms/encoders/encoder0
+
+Last but not least, create one or more connectors::
+
+  sudo mkdir /config/vkms/my-vkms/connectors/connector0
+
+Connectors have 1 configurable attribute:
+
+- status: Connection status: 1 connected, 2 disconnected, 3 unknown (same values
+  as those exposed by the "status" property of a connector)
+
+To finish the configuration, link the different pipeline items::
+
+  sudo ln -s /config/vkms/my-vkms/crtcs/crtc0 /config/vkms/my-vkms/planes/plane0/possible_crtcs
+  sudo ln -s /config/vkms/my-vkms/crtcs/crtc0 /config/vkms/my-vkms/encoders/encoder0/possible_crtcs
+  sudo ln -s /config/vkms/my-vkms/encoders/encoder0 /config/vkms/my-vkms/connectors/connector0/possible_encoders
+
+Since at least one primary plane is required, make sure to set the right type::
+
+  echo "1" | sudo tee /config/vkms/my-vkms/planes/plane0/type
+
+Once you are done configuring the VKMS instance, enable it::
+
+  echo "1" | sudo tee /config/vkms/my-vkms/enabled
+
+Finally, you can remove the VKMS instance disabling it::
+
+  echo "0" | sudo tee /config/vkms/my-vkms/enabled
+
+And removing the top level directory and its subdirectories::
+
+  sudo rm /config/vkms/my-vkms/planes/*/possible_crtcs/*
+  sudo rm /config/vkms/my-vkms/encoders/*/possible_crtcs/*
+  sudo rm /config/vkms/my-vkms/connectors/*/possible_encoders/*
+  sudo rmdir /config/vkms/my-vkms/planes/*
+  sudo rmdir /config/vkms/my-vkms/crtcs/*
+  sudo rmdir /config/vkms/my-vkms/encoders/*
+  sudo rmdir /config/vkms/my-vkms/connectors/*
+  sudo rmdir /config/vkms/my-vkms
+
+Testing With IGT
+================
+
+The IGT GPU Tools is a test suite used specifically for debugging and
+development of the DRM drivers.
+The IGT Tools can be installed from
+`here <https://gitlab.freedesktop.org/drm/igt-gpu-tools>`_ .
+
+The tests need to be run without a compositor, so you need to switch to text
+only mode. You can do this by::
+
+  sudo systemctl isolate multi-user.target
+
+To return to graphical mode, do::
+
+  sudo systemctl isolate graphical.target
+
+Once you are in text only mode, you can run tests using the IGT_FORCE_DRIVER
+variable to specify the device filter for the driver we want to test.
+IGT_FORCE_DRIVER can also be used with the run-tests.sh script to run the
+tests for a specific driver::
+
+  sudo IGT_FORCE_DRIVER="vkms" ./build/tests/<name of test>
+  sudo IGT_FORCE_DRIVER="vkms" ./scripts/run-tests.sh -t <name of test>
+
+For example, to test the functionality of the writeback library,
+we can run the kms_writeback test::
+
+  sudo IGT_FORCE_DRIVER="vkms" ./build/tests/kms_writeback
+  sudo IGT_FORCE_DRIVER="vkms" ./scripts/run-tests.sh -t kms_writeback
+
+You can also run subtests if you do not want to run the entire test::
+
+  sudo IGT_FORCE_DRIVER="vkms" ./build/tests/kms_flip --run-subtest basic-plain-flip
+
+Testing With KUnit
+==================
+
+KUnit (Kernel unit testing framework) provides a common framework for unit tests
+within the Linux kernel.
+More information in ../dev-tools/kunit/index.rst .
+
+To run the VKMS KUnit tests::
+
+  tools/testing/kunit/kunit.py run --kunitconfig=drivers/gpu/drm/vkms/tests
+
+TODO
+====
+
+If you want to do any of the items listed below, please share your interest
+with VKMS maintainers.
+
+IGT better support
+------------------
+
+Debugging:
+
+- kms_plane: some test cases are failing due to timeout on capturing CRC;
+
+Virtual hardware (vblank-less) mode:
+
+- VKMS already has support for vblanks simulated via hrtimers, which can be
+  tested with kms_flip test; in some way, we can say that VKMS already mimics
+  the real hardware vblank. However, we also have virtual hardware that does
+  not support vblank interrupt and completes page_flip events right away; in
+  this case, compositor developers may end up creating a busy loop on virtual
+  hardware. It would be useful to support Virtual Hardware behavior in VKMS
+  because this can help compositor developers to test their features in
+  multiple scenarios.
+
+Add Plane Features
+------------------
+
+There's lots of plane features we could add support for:
+
+- Add background color KMS property[Good to get started].
+
+- Scaling.
+
+- Additional buffer formats. Low/high bpp RGB formats would be interesting
+  [Good to get started].
+
+- Async updates (currently only possible on cursor plane using the legacy
+  cursor api).
+
+For all of these, we also want to review the igt test coverage and make sure
+all relevant igt testcases work on vkms. They are good options for internship
+project.
+
+Runtime Configuration
+---------------------
+
+We want to be able to reconfigure vkms instance without having to reload the
+module through configfs. Use/Test-cases:
+
+- Hotplug/hotremove connectors on the fly (to be able to test DP MST handling
+  of compositors).
+
+- Change output configuration: Plug/unplug screens, change EDID, allow changing
+  the refresh rate.
+
+Writeback support
+-----------------
+
+- The writeback and CRC capture operations share the use of composer_enabled
+  boolean to ensure vblanks. Probably, when these operations work together,
+  composer_enabled needs to refcounting the composer state to proper work.
+  [Good to get started]
+
+- Add support for cloned writeback outputs and related test cases using a
+  cloned output in the IGT kms_writeback.
+
+- As a v4l device. This is useful for debugging compositors on special vkms
+  configurations, so that developers see what's really going on.
+
+Output Features
+---------------
+
+- Variable refresh rate/freesync support. This probably needs prime buffer
+  sharing support, so that we can use vgem fences to simulate rendering in
+  testing. Also needs support to specify the EDID.
+
+- Add support for link status, so that compositors can validate their runtime
+  fallbacks when e.g. a Display Port link goes bad.
+
+CRC API Improvements
+--------------------
+
+- Optimize CRC computation ``compute_crc()`` and plane blending ``blend()``
+
+Atomic Check using eBPF
+-----------------------
+
+Atomic drivers have lots of restrictions which are not exposed to userspace in
+any explicit form through e.g. possible property values. Userspace can only
+inquiry about these limits through the atomic IOCTL, possibly using the
+TEST_ONLY flag. Trying to add configurable code for all these limits, to allow
+compositors to be tested against them, would be rather futile exercise. Instead
+we could add support for eBPF to validate any kind of atomic state, and
+implement a library of different restrictions.
+
+This needs a bunch of features (plane compositing, multiple outputs, ...)
+enabled already to make sense.