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, 354 insertions, 0 deletions

diff --git a/Documentation/rust/quick-start.rst b/Documentation/rust/quick-start.rst
new file mode 100644
index 000000000..f79aa3c71
--- /dev/null
+++ b/Documentation/rust/quick-start.rst
@@ -0,0 +1,354 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Quick Start
+===========
+
+This document describes how to get started with kernel development in Rust.
+
+There are a few ways to install a Rust toolchain needed for kernel development.
+A simple way is to use the packages from your Linux distribution if they are
+suitable -- the first section below explains this approach. An advantage of this
+approach is that, typically, the distribution will match the LLVM used by Rust
+and Clang.
+
+Another way is using the prebuilt stable versions of LLVM+Rust provided on
+`kernel.org <https://kernel.org/pub/tools/llvm/rust/>`_. These are the same slim
+and fast LLVM toolchains from :ref:`Getting LLVM <getting_llvm>` with versions
+of Rust added to them that Rust for Linux supports. Two sets are provided: the
+"latest LLVM" and "matching LLVM" (please see the link for more information).
+
+Alternatively, the next two "Requirements" sections explain each component and
+how to install them through ``rustup``, the standalone installers from Rust
+and/or building them.
+
+The rest of the document explains other aspects on how to get started.
+
+
+Distributions
+-------------
+
+Arch Linux
+**********
+
+Arch Linux provides recent Rust releases and thus it should generally work out
+of the box, e.g.::
+
+	pacman -S rust rust-src rust-bindgen
+
+
+Debian
+******
+
+Debian 13 (Trixie), as well as Testing and Debian Unstable (Sid) provide recent
+Rust releases and thus they should generally work out of the box, e.g.::
+
+	apt install rustc rust-src bindgen rustfmt rust-clippy
+
+
+Fedora Linux
+************
+
+Fedora Linux provides recent Rust releases and thus it should generally work out
+of the box, e.g.::
+
+	dnf install rust rust-src bindgen-cli rustfmt clippy
+
+
+Gentoo Linux
+************
+
+Gentoo Linux provides recent Rust releases and thus it should generally work out
+of the box, e.g.::
+
+	USE='rust-src rustfmt clippy' emerge dev-lang/rust dev-util/bindgen
+
+``LIBCLANG_PATH`` may need to be set.
+
+
+Nix
+***
+
+Nix provides recent Rust releases and thus it should generally work out of the
+box, e.g.::
+
+	{ pkgs ? import <nixpkgs> {} }:
+	pkgs.mkShell {
+	  nativeBuildInputs = with pkgs; [ rustc rust-bindgen rustfmt clippy ];
+	  RUST_LIB_SRC = "${pkgs.rust.packages.stable.rustPlatform.rustLibSrc}";
+	}
+
+
+openSUSE
+********
+
+openSUSE Slowroll and openSUSE Tumbleweed provide recent Rust releases and thus
+they should generally work out of the box, e.g.::
+
+	zypper install rust rust-src rust-bindgen clang
+
+
+Ubuntu
+******
+
+Ubuntu 26.04 LTS provides recent Rust releases and thus it should
+generally work out of the box, e.g.::
+
+	apt install rustc rust-src bindgen rustfmt rust-clippy
+
+In addition, ``RUST_LIB_SRC`` needs to be set, e.g.::
+
+	RUST_LIB_SRC=/usr/src/rustc-$(rustc --version | cut -d' ' -f2)/library
+
+For convenience, ``RUST_LIB_SRC`` can be exported to the global environment.
+
+
+24.04 LTS and older
+~~~~~~~~~~~~~~~~~~~
+
+Though Ubuntu 24.04 LTS and older versions still provide recent Rust
+releases, they require some additional configuration to be set, using
+the versioned packages, e.g.::
+
+	apt install rustc-1.85 rust-1.85-src bindgen-0.71 rustfmt-1.85 \
+		rust-1.85-clippy
+	ln -s /usr/lib/rust-1.85/bin/rustfmt /usr/bin/rustfmt-1.85
+	ln -s /usr/lib/rust-1.85/bin/clippy-driver /usr/bin/clippy-driver-1.85
+
+None of these packages set their tools as defaults; therefore they should be
+specified explicitly, e.g.::
+
+	make LLVM=1 RUSTC=rustc-1.85 RUSTDOC=rustdoc-1.85 RUSTFMT=rustfmt-1.85 \
+		CLIPPY_DRIVER=clippy-driver-1.85 BINDGEN=bindgen-0.71
+
+Alternatively, modify the ``PATH`` variable to place the Rust 1.85 binaries
+first and set ``bindgen`` as the default, e.g.::
+
+	PATH=/usr/lib/rust-1.85/bin:$PATH
+	update-alternatives --install /usr/bin/bindgen bindgen \
+		/usr/bin/bindgen-0.71 100
+	update-alternatives --set bindgen /usr/bin/bindgen-0.71
+
+``RUST_LIB_SRC`` may need to be set when using the versioned packages, e.g.::
+
+	RUST_LIB_SRC=/usr/src/rustc-$(rustc-1.85 --version | cut -d' ' -f2)/library
+
+For convenience, ``RUST_LIB_SRC`` can be exported to the global environment.
+
+In addition, ``bindgen-0.71`` is available in newer releases (24.04 LTS),
+but it may not be available in older ones (20.04 LTS and 22.04 LTS),
+thus ``bindgen`` may need to be built manually (please see below).
+
+
+Requirements: Building
+----------------------
+
+This section explains how to fetch the tools needed for building.
+
+To easily check whether the requirements are met, the following target
+can be used::
+
+	make LLVM=1 rustavailable
+
+This triggers the same logic used by Kconfig to determine whether
+``RUST_IS_AVAILABLE`` should be enabled; but it also explains why not
+if that is the case.
+
+
+rustc
+*****
+
+A recent version of the Rust compiler is required.
+
+If ``rustup`` is being used, enter the kernel build directory (or use
+``--path=<build-dir>`` argument to the ``set`` sub-command) and run,
+for instance::
+
+	rustup override set stable
+
+This will configure your working directory to use the given version of
+``rustc`` without affecting your default toolchain.
+
+Note that the override applies to the current working directory (and its
+sub-directories).
+
+If you are not using ``rustup``, fetch a standalone installer from:
+
+	https://forge.rust-lang.org/infra/other-installation-methods.html#standalone
+
+
+Rust standard library source
+****************************
+
+The Rust standard library source is required because the build system will
+cross-compile ``core``.
+
+If ``rustup`` is being used, run::
+
+	rustup component add rust-src
+
+The components are installed per toolchain, thus upgrading the Rust compiler
+version later on requires re-adding the component.
+
+Otherwise, if a standalone installer is used, the Rust source tree may be
+downloaded into the toolchain's installation folder::
+
+	curl -L "https://static.rust-lang.org/dist/rust-src-$(rustc --version | cut -d' ' -f2).tar.gz" |
+		tar -xzf - -C "$(rustc --print sysroot)/lib" \
+		"rust-src-$(rustc --version | cut -d' ' -f2)/rust-src/lib/" \
+		--strip-components=3
+
+In this case, upgrading the Rust compiler version later on requires manually
+updating the source tree (this can be done by removing ``$(rustc --print
+sysroot)/lib/rustlib/src/rust`` then rerunning the above command).
+
+
+libclang
+********
+
+``libclang`` (part of LLVM) is used by ``bindgen`` to understand the C code
+in the kernel, which means LLVM needs to be installed; like when the kernel
+is compiled with ``LLVM=1``.
+
+Linux distributions are likely to have a suitable one available, so it is
+best to check that first.
+
+There are also some binaries for several systems and architectures uploaded at:
+
+	https://releases.llvm.org/download.html
+
+Otherwise, building LLVM takes quite a while, but it is not a complex process:
+
+	https://llvm.org/docs/GettingStarted.html#getting-the-source-code-and-building-llvm
+
+Please see Documentation/kbuild/llvm.rst for more information and further ways
+to fetch pre-built releases and distribution packages.
+
+
+bindgen
+*******
+
+The bindings to the C side of the kernel are generated at build time using
+the ``bindgen`` tool.
+
+Install it, for instance, via (note that this will download and build the tool
+from source)::
+
+	cargo install --locked bindgen-cli
+
+``bindgen`` uses the ``clang-sys`` crate to find a suitable ``libclang`` (which
+may be linked statically, dynamically or loaded at runtime). By default, the
+``cargo`` command above will produce a ``bindgen`` binary that will load
+``libclang`` at runtime. If it is not found (or a different ``libclang`` than
+the one found should be used), the process can be tweaked, e.g. by using the
+``LIBCLANG_PATH`` environment variable. For details, please see ``clang-sys``'s
+documentation at:
+
+	https://github.com/KyleMayes/clang-sys#linking
+
+	https://github.com/KyleMayes/clang-sys#environment-variables
+
+
+Requirements: Developing
+------------------------
+
+This section explains how to fetch the tools needed for developing. That is,
+they are not needed when just building the kernel.
+
+
+rustfmt
+*******
+
+The ``rustfmt`` tool is used to automatically format all the Rust kernel code,
+including the generated C bindings (for details, please see
+coding-guidelines.rst).
+
+If ``rustup`` is being used, its ``default`` profile already installs the tool,
+thus nothing needs to be done. If another profile is being used, the component
+can be installed manually::
+
+	rustup component add rustfmt
+
+The standalone installers also come with ``rustfmt``.
+
+
+clippy
+******
+
+``clippy`` is a Rust linter. Running it provides extra warnings for Rust code.
+It can be run by passing ``CLIPPY=1`` to ``make`` (for details, please see
+general-information.rst).
+
+If ``rustup`` is being used, its ``default`` profile already installs the tool,
+thus nothing needs to be done. If another profile is being used, the component
+can be installed manually::
+
+	rustup component add clippy
+
+The standalone installers also come with ``clippy``.
+
+
+rustdoc
+*******
+
+``rustdoc`` is the documentation tool for Rust. It generates pretty HTML
+documentation for Rust code (for details, please see
+general-information.rst).
+
+``rustdoc`` is also used to test the examples provided in documented Rust code
+(called doctests or documentation tests). The ``rusttest`` Make target uses
+this feature.
+
+If ``rustup`` is being used, all the profiles already install the tool,
+thus nothing needs to be done.
+
+The standalone installers also come with ``rustdoc``.
+
+
+rust-analyzer
+*************
+
+The `rust-analyzer <https://rust-analyzer.github.io/>`_ language server can
+be used with many editors to enable syntax highlighting, completion, go to
+definition, and other features.
+
+``rust-analyzer`` needs a configuration file, ``rust-project.json``, which
+can be generated by the ``rust-analyzer`` Make target::
+
+	make LLVM=1 rust-analyzer
+
+
+Configuration
+-------------
+
+``Rust support`` (``CONFIG_RUST``) needs to be enabled in the ``General setup``
+menu. The option is only shown if a suitable Rust toolchain is found (see
+above), as long as the other requirements are met. In turn, this will make
+visible the rest of options that depend on Rust.
+
+Afterwards, go to::
+
+	Kernel hacking
+	    -> Sample kernel code
+	        -> Rust samples
+
+And enable some sample modules either as built-in or as loadable.
+
+
+Building
+--------
+
+Building a kernel with a complete LLVM toolchain is the best supported setup
+at the moment. That is::
+
+	make LLVM=1
+
+Using GCC also works for some configurations, but it is very experimental at
+the moment.
+
+
+Hacking
+-------
+
+To dive deeper, take a look at the source code of the samples
+at ``samples/rust/``, the Rust support code under ``rust/`` and
+the ``Rust hacking`` menu under ``Kernel hacking``.