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, 241 insertions, 0 deletions

diff --git a/Documentation/rust/testing.rst b/Documentation/rust/testing.rst
new file mode 100644
index 000000000..e3943acec
--- /dev/null
+++ b/Documentation/rust/testing.rst
@@ -0,0 +1,241 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+Testing
+=======
+
+This document contains useful information how to test the Rust code in the
+kernel.
+
+There are three sorts of tests:
+
+- The KUnit tests.
+- The ``#[test]`` tests.
+- The Kselftests.
+
+The KUnit tests
+---------------
+
+These are the tests that come from the examples in the Rust documentation. They
+get transformed into KUnit tests.
+
+Usage
+*****
+
+These tests can be run via KUnit. For example via ``kunit_tool`` (``kunit.py``)
+on the command line::
+
+	./tools/testing/kunit/kunit.py run --make_options LLVM=1 --arch x86_64 --kconfig_add CONFIG_RUST=y
+
+Alternatively, KUnit can run them as kernel built-in at boot. Refer to
+Documentation/dev-tools/kunit/index.rst for the general KUnit documentation
+and Documentation/dev-tools/kunit/architecture.rst for the details of kernel
+built-in vs. command line testing.
+
+To use these KUnit doctests, the following must be enabled::
+
+	CONFIG_KUNIT
+	   Kernel hacking -> Kernel Testing and Coverage -> KUnit - Enable support for unit tests
+	CONFIG_RUST_KERNEL_DOCTESTS
+	   Kernel hacking -> Rust hacking -> Doctests for the `kernel` crate
+
+in the kernel config system.
+
+KUnit tests are documentation tests
+***********************************
+
+These documentation tests are typically examples of usage of any item (e.g.
+function, struct, module...).
+
+They are very convenient because they are just written alongside the
+documentation. For instance:
+
+.. code-block:: rust
+
+	/// Sums two numbers.
+	///
+	/// ```
+	/// assert_eq!(mymod::f(10, 20), 30);
+	/// ```
+	pub fn f(a: i32, b: i32) -> i32 {
+	    a + b
+	}
+
+In userspace, the tests are collected and run via ``rustdoc``. Using the tool
+as-is would be useful already, since it allows verifying that examples compile
+(thus enforcing they are kept in sync with the code they document) and as well
+as running those that do not depend on in-kernel APIs.
+
+For the kernel, however, these tests get transformed into KUnit test suites.
+This means that doctests get compiled as Rust kernel objects, allowing them to
+run against a built kernel.
+
+A benefit of this KUnit integration is that Rust doctests get to reuse existing
+testing facilities. For instance, the kernel log would look like::
+
+	KTAP version 1
+	1..1
+	    KTAP version 1
+	    # Subtest: rust_doctests_kernel
+	    1..59
+	    # rust_doctest_kernel_build_assert_rs_0.location: rust/kernel/build_assert.rs:13
+	    ok 1 rust_doctest_kernel_build_assert_rs_0
+	    # rust_doctest_kernel_build_assert_rs_1.location: rust/kernel/build_assert.rs:56
+	    ok 2 rust_doctest_kernel_build_assert_rs_1
+	    # rust_doctest_kernel_init_rs_0.location: rust/kernel/init.rs:122
+	    ok 3 rust_doctest_kernel_init_rs_0
+	    ...
+	    # rust_doctest_kernel_types_rs_2.location: rust/kernel/types.rs:150
+	    ok 59 rust_doctest_kernel_types_rs_2
+	# rust_doctests_kernel: pass:59 fail:0 skip:0 total:59
+	# Totals: pass:59 fail:0 skip:0 total:59
+	ok 1 rust_doctests_kernel
+
+Tests using the `? <https://doc.rust-lang.org/reference/expressions/operator-expr.html#the-question-mark-operator>`_
+operator are also supported as usual, e.g.:
+
+.. code-block:: rust
+
+	/// ```
+	/// # use kernel::{spawn_work_item, workqueue};
+	/// spawn_work_item!(workqueue::system(), || pr_info!("x\n"))?;
+	/// # Ok::<(), Error>(())
+	/// ```
+
+The tests are also compiled with Clippy under ``CLIPPY=1``, just like normal
+code, thus also benefitting from extra linting.
+
+In order for developers to easily see which line of doctest code caused a
+failure, a KTAP diagnostic line is printed to the log. This contains the
+location (file and line) of the original test (i.e. instead of the location in
+the generated Rust file)::
+
+	# rust_doctest_kernel_types_rs_2.location: rust/kernel/types.rs:150
+
+Rust tests appear to assert using the usual ``assert!`` and ``assert_eq!``
+macros from the Rust standard library (``core``). We provide a custom version
+that forwards the call to KUnit instead. Importantly, these macros do not
+require passing context, unlike those for KUnit testing (i.e.
+``struct kunit *``). This makes them easier to use, and readers of the
+documentation do not need to care about which testing framework is used. In
+addition, it may allow us to test third-party code more easily in the future.
+
+A current limitation is that KUnit does not support assertions in other tasks.
+Thus, we presently simply print an error to the kernel log if an assertion
+actually failed. Additionally, doctests are not run for nonpublic functions.
+
+Since these tests are examples, i.e. they are part of the documentation, they
+should generally be written like "real code". Thus, for example, instead of
+using ``unwrap()`` or ``expect()``, use the ``?`` operator. For more background,
+please see:
+
+	https://rust.docs.kernel.org/kernel/error/type.Result.html#error-codes-in-c-and-rust
+
+The ``#[test]`` tests
+---------------------
+
+Additionally, there are the ``#[test]`` tests. Like for documentation tests,
+these are also fairly similar to what you would expect from userspace, and they
+are also mapped to KUnit.
+
+These tests are introduced by the ``kunit_tests`` procedural macro, which takes
+the name of the test suite as an argument.
+
+Each test suite should be guarded by a Kconfig option in
+``rust/kernel/Kconfig.test``.
+
+For instance, assume we want to test the function ``f`` from the documentation
+tests section. We could write, in the same file where we have our function:
+
+.. code-block:: rust
+
+	#[cfg(CONFIG_RUST_MYMOD_KUNIT_TEST)]
+	#[kunit_tests(rust_kernel_mymod)]
+	mod tests {
+	    use super::*;
+
+	    #[test]
+	    fn test_f() {
+	        assert_eq!(f(10, 20), 30);
+	    }
+	}
+
+And if we run it, the kernel log would look like::
+
+	    KTAP version 1
+	    # Subtest: rust_kernel_mymod
+	    # speed: normal
+	    1..1
+	    # test_f.speed: normal
+	    ok 1 test_f
+	ok 1 rust_kernel_mymod
+
+Like documentation tests, the ``assert!`` and ``assert_eq!`` macros are mapped
+back to KUnit and do not panic. Similarly, the
+`? <https://doc.rust-lang.org/reference/expressions/operator-expr.html#the-question-mark-operator>`_
+operator is supported, i.e. the test functions may return either nothing (i.e.
+the unit type ``()``) or ``Result`` (i.e. any ``Result<T, E>``). For instance:
+
+.. code-block:: rust
+
+	#[cfg(CONFIG_RUST_MYMOD_KUNIT_TEST)]
+	#[kunit_tests(rust_kernel_mymod)]
+	mod tests {
+	    use super::*;
+
+	    #[test]
+	    fn test_g() -> Result {
+	        let x = g()?;
+	        assert_eq!(x, 30);
+	        Ok(())
+	    }
+	}
+
+If we run the test and the call to ``g`` fails, then the kernel log would show::
+
+	    KTAP version 1
+	    # Subtest: rust_kernel_mymod
+	    # speed: normal
+	    1..1
+	    # test_g: ASSERTION FAILED at rust/kernel/lib.rs:335
+	    Expected is_test_result_ok(test_g()) to be true, but is false
+	    # test_g.speed: normal
+	    not ok 1 test_g
+	not ok 1 rust_kernel_mymod
+
+If a ``#[test]`` test could be useful as an example for the user, then please
+use a documentation test instead. Even edge cases of an API, e.g. error or
+boundary cases, can be interesting to show in examples.
+
+The ``rusttest`` host tests
+---------------------------
+
+These are userspace tests that can be built and run in the host (i.e. the one
+that performs the kernel build) using the ``rusttest`` Make target::
+
+	make LLVM=1 rusttest
+
+This requires the kernel ``.config``.
+
+Currently, they are mostly used for testing the ``macros`` crate's examples.
+
+The Kselftests
+--------------
+
+Kselftests are also available in the ``tools/testing/selftests/rust`` folder.
+
+The kernel config options required for the tests are listed in the
+``tools/testing/selftests/rust/config`` file and can be included with the aid
+of the ``merge_config.sh`` script::
+
+	./scripts/kconfig/merge_config.sh .config tools/testing/selftests/rust/config
+
+The kselftests are built within the kernel source tree and are intended to
+be executed on a system that is running the same kernel.
+
+Once a kernel matching the source tree has been installed and booted, the
+tests can be compiled and executed using the following command::
+
+	make TARGETS="rust" kselftest
+
+Refer to Documentation/dev-tools/kselftest.rst for the general Kselftest
+documentation.