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, 172 insertions, 0 deletions

diff --git a/Documentation/gpu/introduction.rst b/Documentation/gpu/introduction.rst
new file mode 100644
index 000000000..64074ac22
--- /dev/null
+++ b/Documentation/gpu/introduction.rst
@@ -0,0 +1,172 @@
+============
+Introduction
+============
+
+The Linux DRM layer contains code intended to support the needs of
+complex graphics devices, usually containing programmable pipelines well
+suited to 3D graphics acceleration. Graphics drivers in the kernel may
+make use of DRM functions to make tasks like memory management,
+interrupt handling and DMA easier, and provide a uniform interface to
+applications.
+
+A note on versions: this guide covers features found in the DRM tree,
+including the TTM memory manager, output configuration and mode setting,
+and the new vblank internals, in addition to all the regular features
+found in current kernels.
+
+[Insert diagram of typical DRM stack here]
+
+.. contents::
+
+Style Guidelines
+================
+
+For consistency this documentation uses American English. Abbreviations
+are written as all-uppercase, for example: DRM, KMS, IOCTL, CRTC, and so
+on. To aid in reading, documentations make full use of the markup
+characters kerneldoc provides: @parameter for function parameters,
+@member for structure members (within the same structure), &struct structure to
+reference structures and function() for functions. These all get automatically
+hyperlinked if kerneldoc for the referenced objects exists. When referencing
+entries in function vtables (and structure members in general) please use
+&vtable_name.vfunc. Unfortunately this does not yet yield a direct link to the
+member, only the structure.
+
+Except in special situations (to separate locked from unlocked variants)
+locking requirements for functions aren't documented in the kerneldoc.
+Instead locking should be check at runtime using e.g.
+``WARN_ON(!mutex_is_locked(...));``. Since it's much easier to ignore
+documentation than runtime noise this provides more value. And on top of
+that runtime checks do need to be updated when the locking rules change,
+increasing the chances that they're correct. Within the documentation
+the locking rules should be explained in the relevant structures: Either
+in the comment for the lock explaining what it protects, or data fields
+need a note about which lock protects them, or both.
+
+Functions which have a non-\ ``void`` return value should have a section
+called "Returns" explaining the expected return values in different
+cases and their meanings. Currently there's no consensus whether that
+section name should be all upper-case or not, and whether it should end
+in a colon or not. Go with the file-local style. Other common section
+names are "Notes" with information for dangerous or tricky corner cases,
+and "FIXME" where the interface could be cleaned up.
+
+Also read the :ref:`guidelines for the kernel documentation at large <doc_guide>`.
+
+Documentation Requirements for kAPI
+-----------------------------------
+
+All kernel APIs exported to other modules must be documented, including their
+datastructures and at least a short introductory section explaining the overall
+concepts. Documentation should be put into the code itself as kerneldoc comments
+as much as reasonable.
+
+Do not blindly document everything, but document only what's relevant for driver
+authors: Internal functions of drm.ko and definitely static functions should not
+have formal kerneldoc comments. Use normal C comments if you feel like a comment
+is warranted. You may use kerneldoc syntax in the comment, but it shall not
+start with a /** kerneldoc marker. Similar for data structures, annotate
+anything entirely private with ``/* private: */`` comments as per the
+documentation guide.
+
+Getting Started
+===============
+
+Developers interested in helping out with the DRM subsystem are very welcome.
+Often people will resort to sending in patches for various issues reported by
+checkpatch or sparse. We welcome such contributions.
+
+Anyone looking to kick it up a notch can find a list of janitorial tasks on
+the :ref:`TODO list <todo>`.
+
+Contribution Process
+====================
+
+Mostly the DRM subsystem works like any other kernel subsystem, see :ref:`the
+main process guidelines and documentation <process_index>` for how things work.
+Here we just document some of the specialities of the GPU subsystem.
+
+Feature Merge Deadlines
+-----------------------
+
+All feature work must be in the linux-next tree by the -rc6 release of the
+current release cycle, otherwise they must be postponed and can't reach the next
+merge window. All patches must have landed in the drm-next tree by latest -rc7,
+but if your branch is not in linux-next then this must have happened by -rc6
+already.
+
+After that point only bugfixes (like after the upstream merge window has closed
+with the -rc1 release) are allowed. No new platform enabling or new drivers are
+allowed.
+
+This means that there's a blackout-period of about one month where feature work
+can't be merged. The recommended way to deal with that is having a -next tree
+that's always open, but making sure to not feed it into linux-next during the
+blackout period. As an example, drm-misc works like that.
+
+Code of Conduct
+---------------
+
+As a freedesktop.org project, dri-devel, and the DRM community, follows the
+Contributor Covenant, found at: https://www.freedesktop.org/wiki/CodeOfConduct
+
+Please conduct yourself in a respectful and civilised manner when
+interacting with community members on mailing lists, IRC, or bug
+trackers. The community represents the project as a whole, and abusive
+or bullying behaviour is not tolerated by the project.
+
+Simple DRM drivers to use as examples
+=====================================
+
+The DRM subsystem contains a lot of helper functions to ease writing drivers for
+simple graphic devices. For example, the `drivers/gpu/drm/tiny/` directory has a
+set of drivers that are simple enough to be implemented in a single source file.
+The tiny DRM drivers are good examples to understand how DRM drivers should look
+like. Since are just a few hundreds lines of code, they are quite easy to read.
+
+External References
+===================
+
+Delving into a Linux kernel subsystem for the first time can be an overwhelming
+experience, one needs to get familiar with all the concepts and learn about the
+subsystem's internals, among other details.
+
+To shallow the learning curve, this section contains a list of presentations
+and documents that can be used to learn about DRM/KMS and graphics in general.
+
+There are different reasons why someone might want to get into DRM: porting an
+existing fbdev driver, write a DRM driver for a new hardware, fixing bugs that
+could face when working on the graphics user-space stack, etc. For this reason,
+the learning material covers many aspects of the Linux graphics stack. From an
+overview of the kernel and user-space stacks to very specific topics.
+
+The list is sorted in reverse chronological order, to keep the most up-to-date
+material at the top. But all of them contain useful information, and it can be
+valuable to go through older material to understand the rationale and context
+in which the changes to the DRM subsystem were made.
+
+Conference talks
+----------------
+
+* `An Overview of the Linux and Userspace Graphics Stack <https://www.youtube.com/watch?v=wjAJmqwg47k>`_ - Paul Kocialkowski (2020)
+* `Getting pixels on screen on Linux: introduction to Kernel Mode Setting <https://www.youtube.com/watch?v=haes4_Xnc5Q>`_ - Simon Ser (2020)
+* `Everything Great about Upstream Graphics <https://www.youtube.com/watch?v=kVzHOgt6WGE>`_ - Simona Vetter (2019)
+* `An introduction to the Linux DRM subsystem <https://www.youtube.com/watch?v=LbDOCJcDRoo>`_ - Maxime Ripard (2017)
+* `Embrace the Atomic (Display) Age <https://www.youtube.com/watch?v=LjiB_JeDn2M>`_ - Simona Vetter (2016)
+* `Anatomy of an Atomic KMS Driver <https://www.youtube.com/watch?v=lihqR9sENpc>`_ - Laurent Pinchart (2015)
+* `Atomic Modesetting for Drivers <https://www.youtube.com/watch?v=kl9suFgbTc8>`_ - Simona Vetter (2015)
+* `Anatomy of an Embedded KMS Driver <https://www.youtube.com/watch?v=Ja8fM7rTae4>`_ - Laurent Pinchart (2013)
+
+Slides and articles
+-------------------
+
+* `The Linux graphics stack in a nutshell, part 1 <https://lwn.net/Articles/955376/>`_ - Thomas Zimmermann (2023)
+* `The Linux graphics stack in a nutshell, part 2 <https://lwn.net/Articles/955708/>`_ - Thomas Zimmermann (2023)
+* `Understanding the Linux Graphics Stack <https://bootlin.com/doc/training/graphics/graphics-slides.pdf>`_ - Bootlin (2022)
+* `DRM KMS overview <https://wiki.st.com/stm32mpu/wiki/DRM_KMS_overview>`_ - STMicroelectronics (2021)
+* `Linux graphic stack <https://studiopixl.com/2017-05-13/linux-graphic-stack-an-overview>`_ - Nathan Gauër (2017)
+* `Atomic mode setting design overview, part 1 <https://lwn.net/Articles/653071/>`_ - Simona Vetter (2015)
+* `Atomic mode setting design overview, part 2 <https://lwn.net/Articles/653466/>`_ - Simona Vetter (2015)
+* `The DRM/KMS subsystem from a newbie’s point of view <https://bootlin.com/pub/conferences/2014/elce/brezillon-drm-kms/brezillon-drm-kms.pdf>`_ - Boris Brezillon (2014)
+* `A brief introduction to the Linux graphics stack <https://blogs.igalia.com/itoral/2014/07/29/a-brief-introduction-to-the-linux-graphics-stack/>`_ - Iago Toral (2014)
+* `The Linux Graphics Stack <https://blog.mecheye.net/2012/06/the-linux-graphics-stack/>`_ - Jasper St. Pierre (2012)