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, 195 insertions, 0 deletions

diff --git a/Documentation/filesystems/adding-new-filesystems.rst b/Documentation/filesystems/adding-new-filesystems.rst
new file mode 100644
index 000000000..a3d0bf16f
--- /dev/null
+++ b/Documentation/filesystems/adding-new-filesystems.rst
@@ -0,0 +1,195 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+.. _adding_new_filesystems:
+
+Adding New Filesystems
+======================
+
+This document describes what is involved in adding a new filesystem to the
+Linux kernel.
+
+Every filesystem merged into the kernel becomes the collective responsibility
+of the VFS maintainers and the wider filesystem development community.
+Experience has shown that filesystems which become unmaintained impose a
+significant and ongoing burden: they are hard or impossible to test, they
+block infrastructure changes because someone must update or preserve old APIs
+for code that nobody is actively looking after, and they accumulate unfixed
+bugs.  The requirements and expectations described here are informed by this
+experience and are intended to ensure that new filesystems enter the kernel
+on a sustainable footing.
+
+
+Do You Need a New In-Kernel Filesystem?
+---------------------------------------
+
+Before proposing a new in-kernel filesystem, consider whether one of the
+alternatives might be more appropriate.
+
+ - If an existing in-kernel filesystem covers the same use case, improving it
+   is generally preferred over adding a new implementation.  The kernel
+   community favors incremental improvement over parallel implementations.
+
+ - If the filesystem serves a niche audience or has a small user base, a FUSE
+   (Filesystem in Userspace) implementation may be a better fit.  FUSE
+   filesystems avoid the long-term kernel maintenance commitment and can be
+   developed and released on their own schedule.
+
+ - If kernel-level performance, reliability, or integration is genuinely
+   required, make the case explicitly.  Explain who the users are, what the
+   use case is, and why a FUSE implementation would not be sufficient.
+
+
+Technical Requirements
+----------------------
+
+New filesystems must use current kernel interfaces and practices.
+Submitting a filesystem built on outdated APIs creates an unacceptable
+maintenance debt and is likely to face pushback during review.
+
+Use modern VFS interfaces
+  Do not use interfaces listed in
+  :ref:`Documentation/process/deprecated.rst <deprecated>`.
+
+  Use folios rather than raw page operations for page cache management and
+  iomap rather than buffer heads for block mapping and I/O.  See
+  ``Documentation/filesystems/iomap/index.rst`` for iomap documentation.
+
+  Block-based filesystems that need functionality not currently provided by
+  iomap should be prepared to explain why adding that functionality to iomap
+  is infeasible, rather than reimplementing their own block mapping layer.
+
+  Network filesystems should consider using the netfs library
+  (``Documentation/filesystems/netfs_library.rst``), or be prepared to explain
+  why it is not a good fit.
+
+Provide userspace utilities
+  A ``mkfs`` tool is expected so that the filesystem can be created and used
+  by testers and users.  A ``fsck`` tool is strongly recommended; while not
+  strictly required for every filesystem type, the ability to verify
+  consistency and repair corruption is an important part of a mature
+  filesystem.
+
+Be testable
+  The filesystem must be testable in a meaningful way.  The
+  `fstests <https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git>`_
+  framework (also known as xfstests) is the standard testing infrastructure
+  for Linux filesystems and its use is highly recommended.  At a minimum,
+  there must be a credible and documented way to test the filesystem and
+  detect regressions.  When submitting, include a summary of test results
+  indicating which tests pass, fail, or are not applicable.
+
+Provide documentation
+  A documentation file under ``Documentation/filesystems/`` describing the
+  filesystem, its on-disk format, mount options, and any notable design
+  decisions is recommended.
+
+
+Community and Maintainership Expectations
+-----------------------------------------
+
+Merging a filesystem is a long-term commitment.  The kernel community
+needs confidence that the filesystem will be actively maintained after it
+is merged.
+
+Identified maintainers
+  The submission must include a ``MAINTAINERS`` entry with at least one
+  maintainer (``M:``), a mailing list (``L:``), and a git tree (``T:``).
+  Having two or more maintainers is strongly preferred so that coverage
+  does not depend on a single person.  The maintainers are expected to be
+  the primary points of contact for the filesystem going forward.
+
+Demonstrated commitment
+  A track record of maintaining kernel code -- for example, in other
+  subsystems -- significantly strengthens the case for a new filesystem.
+  Maintainers who are already known and trusted within the community face
+  less friction during review.
+
+Sustained backing
+  Major filesystems in Linux have organizational or corporate support behind
+  their development.  Filesystems that depend entirely on volunteer effort
+  face higher scrutiny about their long-term viability.
+
+Responsiveness
+  The maintainer is expected to respond to bug reports, address review
+  feedback, and adapt the filesystem to VFS infrastructure changes such as
+  folio conversions, iomap migration, and mount API updates.  Unresponsive
+  maintainership is one of the primary reasons filesystems end up on the
+  path to deprecation.
+
+User base
+  Clearly describe who the users of this filesystem are and the scale of the
+  user base.  Filesystems with a very small or unclear user base face a
+  harder path to acceptance and a higher risk of future deprecation.
+
+Building your track record
+  A practical way to demonstrate many of the qualities above is to maintain
+  the filesystem out-of-tree for a period before requesting a merge.  This
+  shows sustained commitment, builds a visible user base, and gives reviewers
+  confidence that the code and its maintainer will persist after merging.
+  That said, it is recognized that for some filesystems the user base grows
+  significantly only after upstreaming, so a compelling case for expected
+  adoption can substitute for a large existing user base.
+
+
+Submission Process
+------------------
+
+This section covers what is specific to filesystem submissions, over and
+above the normal submission advice in
+:ref:`Documentation/process/submitting-patches.rst <submittingpatches>` and
+:ref:`Documentation/process/submit-checklist.rst <submitchecklist>`.
+
+ - Send patches to the linux-fsdevel mailing list
+   (``linux-fsdevel@vger.kernel.org``).  CC the relevant VFS maintainers as
+   listed in the ``MAINTAINERS`` file under
+   ``FILESYSTEMS (VFS and infrastructure)``.
+
+ - Structure the submission logically.  It is neither acceptable to send one
+   large patch containing the entire filesystem, nor is a replay of the full
+   development history helpful to reviewers.  Instead, split the series by
+   topic -- for example: superblock and mount handling, inode operations,
+   directory operations, address space operations, and so on -- so that each
+   patch is reviewable in isolation.
+
+ - Separate any filesystem-specific ioctls into their own patches with
+   dedicated justification.  Interfaces beyond those already common across
+   other filesystems will receive additional scrutiny because they are hard
+   to maintain and may conflict with future generic interfaces.
+
+ - Expect thorough review.  Filesystem code interacts deeply with the VFS,
+   memory management, and block layers, so reviewers will examine the code
+   carefully.  Address all review feedback and be prepared for multiple
+   revision cycles.
+
+ - It may be appropriate to mark the filesystem as experimental in its Kconfig
+   help text for the first few releases to set expectations while the code
+   stabilizes in-tree.
+
+
+Ongoing Obligations
+-------------------
+
+Merging is not the finish line.  Maintaining a filesystem in the kernel is an
+ongoing commitment.
+
+ - Adapt to VFS infrastructure changes.  The VFS layer evolves continuously;
+   maintainers are expected to keep up with conversions such as folio
+   migration, iomap adoption, and mount API updates.
+
+ - Maintain test coverage.  As test suites evolve, the filesystem's test
+   results should be kept current.
+
+ - Handle security issues and regression promptly.  Both those reported
+   by ordinary users and those reported by test bots and fuzzing tools.
+   The filesystem must handle corrupted input gracefully without corrupting
+   memory, hanging, or crashing the kernel.
+
+ - Engage with the wider filesystem community.  Participate on linux-fsdevel,
+   share approaches to common problems, and look for opportunities to reuse
+   shared infrastructure.  It is inappropriate to develop in isolation on a
+   private list and surface patches only at merge time.
+
+ - Filesystems that become unmaintained -- where the maintainer stops
+   responding, infrastructure changes go unadapted, and testing becomes
+   impossible -- are candidates for deprecation and eventual removal from
+   the kernel.