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, 209 insertions, 0 deletions

diff --git a/Documentation/dev-tools/autofdo.rst b/Documentation/dev-tools/autofdo.rst
new file mode 100644
index 000000000..ae03c4dfe
--- /dev/null
+++ b/Documentation/dev-tools/autofdo.rst
@@ -0,0 +1,209 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+Using AutoFDO with the Linux kernel
+===================================
+
+This enables AutoFDO build support for the kernel when using
+the Clang compiler. AutoFDO (Auto-Feedback-Directed Optimization)
+is a type of profile-guided optimization (PGO) used to enhance the
+performance of binary executables. It gathers information about the
+frequency of execution of various code paths within a binary using
+hardware sampling. This data is then used to guide the compiler's
+optimization decisions, resulting in a more efficient binary. AutoFDO
+is a powerful optimization technique, and data indicates that it can
+significantly improve kernel performance. It's especially beneficial
+for workloads affected by front-end stalls.
+
+For AutoFDO builds, unlike non-FDO builds, the user must supply a
+profile. Acquiring an AutoFDO profile can be done in several ways.
+AutoFDO profiles are created by converting hardware sampling using
+the "perf" tool. It is crucial that the workload used to create these
+perf files is representative; they must exhibit runtime
+characteristics similar to the workloads that are intended to be
+optimized. Failure to do so will result in the compiler optimizing
+for the wrong objective.
+
+The AutoFDO profile often encapsulates the program's behavior. If the
+performance-critical codes are architecture-independent, the profile
+can be applied across platforms to achieve performance gains. For
+instance, using the profile generated on Intel architecture to build
+a kernel for AMD architecture can also yield performance improvements.
+
+There are two methods for acquiring a representative profile:
+(1) Sample real workloads using a production environment.
+(2) Generate the profile using a representative load test.
+When enabling the AutoFDO build configuration without providing an
+AutoFDO profile, the compiler only modifies the dwarf information in
+the kernel without impacting runtime performance. It's advisable to
+use a kernel binary built with the same AutoFDO configuration to
+collect the perf profile. While it's possible to use a kernel built
+with different options, it may result in inferior performance.
+
+One can collect profiles using AutoFDO build for the previous kernel.
+AutoFDO employs relative line numbers to match the profiles, offering
+some tolerance for source changes. This mode is commonly used in a
+production environment for profile collection.
+
+In a profile collection based on a load test, the AutoFDO collection
+process consists of the following steps:
+
+#. Initial build: The kernel is built with AutoFDO options
+   without a profile.
+
+#. Profiling: The above kernel is then run with a representative
+   workload to gather execution frequency data. This data is
+   collected using hardware sampling, via perf. AutoFDO is most
+   effective on platforms supporting advanced PMU features like
+   LBR on Intel machines.
+
+#. AutoFDO profile generation: Perf output file is converted to
+   the AutoFDO profile via offline tools.
+
+The support requires a Clang compiler LLVM 17 or later.
+Current supported architectures include x86/x86_64 (via LBR) and
+arm64 (via SPE or ETM).
+
+
+Preparation
+===========
+
+Configure the kernel with::
+
+   CONFIG_AUTOFDO_CLANG=y
+
+Customization
+=============
+
+The default CONFIG_AUTOFDO_CLANG setting covers kernel space objects for
+AutoFDO builds. One can, however, enable or disable AutoFDO build for
+individual files and directories by adding a line similar to the following
+to the respective kernel Makefile:
+
+- For enabling a single file (e.g. foo.o) ::
+
+   AUTOFDO_PROFILE_foo.o := y
+
+- For enabling all files in one directory ::
+
+   AUTOFDO_PROFILE := y
+
+- For disabling one file ::
+
+   AUTOFDO_PROFILE_foo.o := n
+
+- For disabling all files in one directory ::
+
+   AUTOFDO_PROFILE := n
+
+Workflow
+========
+
+Here is an example workflow for AutoFDO kernel:
+
+1)  Build the kernel on the host machine with LLVM enabled,
+    for example, ::
+
+      $ make menuconfig LLVM=1
+
+    Turn on AutoFDO build config::
+
+      CONFIG_AUTOFDO_CLANG=y
+
+    With a configuration that with LLVM enabled, use the following command::
+
+      $ scripts/config -e AUTOFDO_CLANG
+
+    After getting the config, build with ::
+
+      $ make LLVM=1
+
+2) Install the kernel on the test machine.
+
+3) Run the load tests. The '-c' option in perf specifies the sample
+   event period. We suggest using a suitable prime number, like 500009,
+   for this purpose.
+
+   - For Intel platforms::
+
+      $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+   - For AMD platforms:
+
+     The supported systems are: Zen3 with BRS, or Zen4 with amd_lbr_v2. To check,
+
+     For Zen3::
+
+      $ cat /proc/cpuinfo | grep " brs"
+
+     For Zen4::
+
+      $ cat /proc/cpuinfo | grep amd_lbr_v2
+
+     The following command generated the perf data file::
+
+      $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+   - For arm64 with SPE:
+
+     There are a few kernel features that must be enabled to collect SPE profiles on Arm.
+     Below is a list of the required features:
+
+      - CONFIG_ARM_SPE_PMU=y
+      - CONFIG_PID_IN_CONTEXTIDR=y
+      - kpti=off
+
+     Use the following command to generate SPE perf data file::
+
+      $ perf record -e ' arm_spe_0/branch_filter=1,load_filter=0,store_filter=0/'  -a -c <count> -N --no-switch-events -o <perf_file> -- <loadtest>
+
+   - For arm64 with ETM trace:
+
+     Follow the instructions in `Linaro OpenCSD document
+     <https://github.com/Linaro/OpenCSD/blob/master/decoder/tests/auto-fdo/autofdo.md>`_
+     to record ETM traces for AutoFDO::
+
+      $ perf record -e cs_etm/@tmc_etr0/k -a -o <etm_perf_file> -- <loadtest>
+      $ perf inject -i <etm_perf_file> -o <perf_file> --itrace=i500009il
+
+     For ARM platforms running Android, follow the instructions in `Android simpleperf
+     document <https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/gki/aarch64/afdo>`_
+     to record ETM traces for AutoFDO::
+
+      $ simpleperf record -e cs-etm:k -a -o <etm_perf_file> -- <loadtest>
+      $ simpleperf inject -i <etm_perf_file> -o <text_perf_file> --symdir <vmlinux_dir>
+
+4) (Optional) Download the raw perf file to the host machine.
+
+5) To generate an AutoFDO profile, two offline tools are available:
+   create_llvm_prof and llvm_profgen. The create_llvm_prof tool is part
+   of the AutoFDO project and can be found on GitHub
+   (https://github.com/google/autofdo), version v0.30.1 or later.
+   The llvm_profgen tool is included in the LLVM compiler itself. It's
+   important to note that the version of llvm_profgen doesn't need to match
+   the version of Clang. It needs to be the LLVM 19 release of Clang
+   or later, or just from the LLVM trunk. ::
+
+      $ llvm-profgen --kernel --binary=<vmlinux> --perfdata=<perf_file> -o <profile_file>
+
+   or ::
+
+      $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> --format=extbinary --out=<profile_file>
+
+   Note that multiple AutoFDO profile files can be merged into one via::
+
+      $ llvm-profdata merge -o <profile_file> <profile_1> <profile_2> ... <profile_n>
+
+   For arm64 SPE, use the following command::
+
+      $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> --profiler=perf_spe --format=extbinary --out=<profile_file>
+
+   For arm64 ETM, use the following command::
+
+      $ create_llvm_prof --binary=<vmlinux> --profile=<text_perf_file> --profiler=text -format=extbinary -out=<profile_file>
+
+
+6) Rebuild the kernel using the AutoFDO profile file with the same config as step 1,
+   (Note CONFIG_AUTOFDO_CLANG needs to be enabled)::
+
+      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file>