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, 285 insertions, 0 deletions

diff --git a/Documentation/dev-tools/gcov.rst b/Documentation/dev-tools/gcov.rst
new file mode 100644
index 000000000..075df6a45
--- /dev/null
+++ b/Documentation/dev-tools/gcov.rst
@@ -0,0 +1,285 @@
+Using gcov with the Linux kernel
+================================
+
+gcov profiling kernel support enables the use of GCC's coverage testing
+tool gcov_ with the Linux kernel. Coverage data of a running kernel
+is exported in gcov-compatible format via the "gcov" debugfs directory.
+To get coverage data for a specific file, change to the kernel build
+directory and use gcov with the ``-o`` option as follows (requires root)::
+
+    # cd /tmp/linux-out
+    # gcov -o /sys/kernel/debug/gcov/tmp/linux-out/kernel spinlock.c
+
+This will create source code files annotated with execution counts
+in the current directory. In addition, graphical gcov front-ends such
+as lcov_ can be used to automate the process of collecting data
+for the entire kernel and provide coverage overviews in HTML format.
+
+Possible uses:
+
+* debugging (has this line been reached at all?)
+* test improvement (how do I change my test to cover these lines?)
+* minimizing kernel configurations (do I need this option if the
+  associated code is never run?)
+
+.. _gcov: https://gcc.gnu.org/onlinedocs/gcc/Gcov.html
+.. _lcov: https://github.com/linux-test-project/lcov
+
+
+Preparation
+-----------
+
+Configure the kernel with::
+
+        CONFIG_DEBUG_FS=y
+        CONFIG_GCOV_KERNEL=y
+
+and to get coverage data for the entire kernel::
+
+        CONFIG_GCOV_PROFILE_ALL=y
+
+Note that kernels compiled with profiling flags will be significantly
+larger and run slower. Also CONFIG_GCOV_PROFILE_ALL may not be supported
+on all architectures.
+
+Profiling data will only become accessible once debugfs has been
+mounted::
+
+        mount -t debugfs none /sys/kernel/debug
+
+
+Customization
+-------------
+
+To enable profiling for specific files or directories, add a line
+similar to the following to the respective kernel Makefile:
+
+- For a single file (e.g. main.o)::
+
+	GCOV_PROFILE_main.o := y
+
+- For all files in one directory::
+
+	GCOV_PROFILE := y
+
+To exclude files from being profiled even when CONFIG_GCOV_PROFILE_ALL
+is specified, use::
+
+	GCOV_PROFILE_main.o := n
+
+and::
+
+	GCOV_PROFILE := n
+
+Only files which are linked to the main kernel image or are compiled as
+kernel modules are supported by this mechanism.
+
+
+Module specific configs
+-----------------------
+
+Gcov kernel configs for specific modules are described below:
+
+CONFIG_GCOV_PROFILE_RDS:
+        Enables GCOV profiling on RDS for checking which functions or
+        lines are executed. This config is used by the rds selftest to
+        generate coverage reports. If left unset the report is omitted.
+
+
+Files
+-----
+
+The gcov kernel support creates the following files in debugfs:
+
+``/sys/kernel/debug/gcov``
+	Parent directory for all gcov-related files.
+
+``/sys/kernel/debug/gcov/reset``
+	Global reset file: resets all coverage data to zero when
+        written to.
+
+``/sys/kernel/debug/gcov/path/to/compile/dir/file.gcda``
+	The actual gcov data file as understood by the gcov
+        tool. Resets file coverage data to zero when written to.
+
+``/sys/kernel/debug/gcov/path/to/compile/dir/file.gcno``
+	Symbolic link to a static data file required by the gcov
+        tool. This file is generated by gcc when compiling with
+        option ``-ftest-coverage``.
+
+
+Modules
+-------
+
+Kernel modules may contain cleanup code which is only run during
+module unload time. The gcov mechanism provides a means to collect
+coverage data for such code by keeping a copy of the data associated
+with the unloaded module. This data remains available through debugfs.
+Once the module is loaded again, the associated coverage counters are
+initialized with the data from its previous instantiation.
+
+This behavior can be deactivated by specifying the gcov_persist kernel
+parameter::
+
+        gcov_persist=0
+
+At run-time, a user can also choose to discard data for an unloaded
+module by writing to its data file or the global reset file.
+
+
+Separated build and test machines
+---------------------------------
+
+The gcov kernel profiling infrastructure is designed to work out-of-the
+box for setups where kernels are built and run on the same machine. In
+cases where the kernel runs on a separate machine, special preparations
+must be made, depending on where the gcov tool is used:
+
+.. _gcov-test:
+
+a) gcov is run on the TEST machine
+
+    The gcov tool version on the test machine must be compatible with the
+    gcc version used for kernel build. Also the following files need to be
+    copied from build to test machine:
+
+    from the source tree:
+      - all C source files + headers
+
+    from the build tree:
+      - all C source files + headers
+      - all .gcda and .gcno files
+      - all links to directories
+
+    It is important to note that these files need to be placed into the
+    exact same file system location on the test machine as on the build
+    machine. If any of the path components is symbolic link, the actual
+    directory needs to be used instead (due to make's CURDIR handling).
+
+.. _gcov-build:
+
+b) gcov is run on the BUILD machine
+
+    The following files need to be copied after each test case from test
+    to build machine:
+
+    from the gcov directory in sysfs:
+      - all .gcda files
+      - all links to .gcno files
+
+    These files can be copied to any location on the build machine. gcov
+    must then be called with the -o option pointing to that directory.
+
+    Example directory setup on the build machine::
+
+      /tmp/linux:    kernel source tree
+      /tmp/out:      kernel build directory as specified by make O=
+      /tmp/coverage: location of the files copied from the test machine
+
+      [user@build] cd /tmp/out
+      [user@build] gcov -o /tmp/coverage/tmp/out/init main.c
+
+
+Note on compilers
+-----------------
+
+GCC and LLVM gcov tools are not necessarily compatible. Use gcov_ to work with
+GCC-generated .gcno and .gcda files, and use llvm-cov_ for Clang.
+
+.. _gcov: https://gcc.gnu.org/onlinedocs/gcc/Gcov.html
+.. _llvm-cov: https://llvm.org/docs/CommandGuide/llvm-cov.html
+
+Build differences between GCC and Clang gcov are handled by Kconfig. It
+automatically selects the appropriate gcov format depending on the detected
+toolchain.
+
+
+Troubleshooting
+---------------
+
+Problem
+    Compilation aborts during linker step.
+
+Cause
+    Profiling flags are specified for source files which are not
+    linked to the main kernel or which are linked by a custom
+    linker procedure.
+
+Solution
+    Exclude affected source files from profiling by specifying
+    ``GCOV_PROFILE := n`` or ``GCOV_PROFILE_basename.o := n`` in the
+    corresponding Makefile.
+
+Problem
+    Files copied from sysfs appear empty or incomplete.
+
+Cause
+    Due to the way seq_file works, some tools such as cp or tar
+    may not correctly copy files from sysfs.
+
+Solution
+    Use ``cat`` to read ``.gcda`` files and ``cp -d`` to copy links.
+    Alternatively use the mechanism shown in Appendix B.
+
+
+Appendix A: gather_on_build.sh
+------------------------------
+
+Sample script to gather coverage meta files on the build machine
+(see :ref:`Separated build and test machines a. <gcov-test>`):
+
+.. code-block:: sh
+
+    #!/bin/bash
+
+    KSRC=$1
+    KOBJ=$2
+    DEST=$3
+
+    if [ -z "$KSRC" ] || [ -z "$KOBJ" ] || [ -z "$DEST" ]; then
+      echo "Usage: $0 <ksrc directory> <kobj directory> <output.tar.gz>" >&2
+      exit 1
+    fi
+
+    KSRC=$(cd $KSRC; printf "all:\n\t@echo \${CURDIR}\n" | make -f -)
+    KOBJ=$(cd $KOBJ; printf "all:\n\t@echo \${CURDIR}\n" | make -f -)
+
+    find $KSRC $KOBJ \( -name '*.gcno' -o -name '*.[ch]' -o -type l \) -a \
+                     -perm /u+r,g+r | tar cfz $DEST -P -T -
+
+    if [ $? -eq 0 ] ; then
+      echo "$DEST successfully created, copy to test system and unpack with:"
+      echo "  tar xfz $DEST -P"
+    else
+      echo "Could not create file $DEST"
+    fi
+
+
+Appendix B: gather_on_test.sh
+-----------------------------
+
+Sample script to gather coverage data files on the test machine
+(see :ref:`Separated build and test machines b. <gcov-build>`):
+
+.. code-block:: sh
+
+    #!/bin/bash -e
+
+    DEST=$1
+    GCDA=/sys/kernel/debug/gcov
+
+    if [ -z "$DEST" ] ; then
+      echo "Usage: $0 <output.tar.gz>" >&2
+      exit 1
+    fi
+
+    TEMPDIR=$(mktemp -d)
+    echo Collecting data..
+    find $GCDA -type d -exec mkdir -p $TEMPDIR/\{\} \;
+    find $GCDA -name '*.gcda' -exec sh -c 'cat < $0 > '$TEMPDIR'/$0' {} \;
+    find $GCDA -name '*.gcno' -exec sh -c 'cp -d $0 '$TEMPDIR'/$0' {} \;
+    tar czf $DEST -C $TEMPDIR sys
+    rm -rf $TEMPDIR
+
+    echo "$DEST successfully created, copy to build system and unpack with:"
+    echo "  tar xfz $DEST"