diff options
Diffstat (limited to 'Documentation/process')
| -rw-r--r-- | Documentation/process/5.Posting.rst | 5 | ||||
| -rw-r--r-- | Documentation/process/backporting.rst | 8 | ||||
| -rw-r--r-- | Documentation/process/changes.rst | 2 | ||||
| -rw-r--r-- | Documentation/process/code-of-conduct-interpretation.rst | 87 | ||||
| -rw-r--r-- | Documentation/process/debugging/driver_development_debugging_guide.rst | 223 | ||||
| -rw-r--r-- | Documentation/process/debugging/index.rst | 78 | ||||
| -rw-r--r-- | Documentation/process/debugging/media_specific_debugging_guide.rst | 180 | ||||
| -rw-r--r-- | Documentation/process/debugging/userspace_debugging_guide.rst | 280 | ||||
| -rw-r--r-- | Documentation/process/index.rst | 8 | ||||
| -rw-r--r-- | Documentation/process/kernel-docs.rst | 163 | ||||
| -rw-r--r-- | Documentation/process/license-rules.rst | 18 | ||||
| -rw-r--r-- | Documentation/process/maintainer-tip.rst | 4 |
12 files changed, 1022 insertions, 34 deletions
diff --git a/Documentation/process/5.Posting.rst b/Documentation/process/5.Posting.rst index de4edd42d5c0..b3eff03ea249 100644 --- a/Documentation/process/5.Posting.rst +++ b/Documentation/process/5.Posting.rst @@ -191,11 +191,6 @@ change to a revision control system. It will be followed by: option to diff will associate function names with changes, making the resulting patch easier for others to read. -You should avoid including changes to irrelevant files (those generated by -the build process, for example, or editor backup files) in the patch. The -file "dontdiff" in the Documentation directory can help in this regard; -pass it to diff with the "-X" option. - The tags already briefly mentioned above are used to provide insights how the patch came into being. They are described in detail in the :ref:`Documentation/process/submitting-patches.rst <submittingpatches>` diff --git a/Documentation/process/backporting.rst b/Documentation/process/backporting.rst index a71480fcf3b4..c42779fbcd33 100644 --- a/Documentation/process/backporting.rst +++ b/Documentation/process/backporting.rst @@ -74,7 +74,7 @@ your source tree. Don't forget to cherry-pick with ``-x`` if you want a written record of where the patch came from! Note that if you are submitting a patch for stable, the format is -slightly different; the first line after the subject line needs tobe +slightly different; the first line after the subject line needs to be either:: commit <upstream commit> upstream @@ -553,7 +553,7 @@ Submitting backports to stable ============================== As the stable maintainers try to cherry-pick mainline fixes onto their -stable kernels, they may send out emails asking for backports when when +stable kernels, they may send out emails asking for backports when encountering conflicts, see e.g. <https://lore.kernel.org/stable/2023101528-jawed-shelving-071a@gregkh/>. These emails typically include the exact steps you need to cherry-pick @@ -563,9 +563,9 @@ One thing to make sure is that your changelog conforms to the expected format:: <original patch title> - + [ Upstream commit <mainline rev> ] - + <rest of the original changelog> [ <summary of the conflicts and their resolutions> ] Signed-off-by: <your name and email> diff --git a/Documentation/process/changes.rst b/Documentation/process/changes.rst index 00f1ed7c59c3..82b5e378eebf 100644 --- a/Documentation/process/changes.rst +++ b/Documentation/process/changes.rst @@ -46,7 +46,7 @@ jfsutils 1.1.3 fsck.jfs -V reiserfsprogs 3.6.3 reiserfsck -V xfsprogs 2.6.0 xfs_db -V squashfs-tools 4.0 mksquashfs -version -btrfs-progs 0.18 btrfsck +btrfs-progs 0.18 btrfs --version pcmciautils 004 pccardctl -V quota-tools 3.09 quota -V PPP 2.4.0 pppd --version diff --git a/Documentation/process/code-of-conduct-interpretation.rst b/Documentation/process/code-of-conduct-interpretation.rst index 66b07f14714c..1d1150954be3 100644 --- a/Documentation/process/code-of-conduct-interpretation.rst +++ b/Documentation/process/code-of-conduct-interpretation.rst @@ -156,3 +156,90 @@ overridden decisions including complete and identifiable voting details. Because how we interpret and enforce the Code of Conduct will evolve over time, this document will be updated when necessary to reflect any changes. + +Enforcement for Unacceptable Behavior Code of Conduct Violations +---------------------------------------------------------------- + +The Code of Conduct committee works to ensure that our community continues +to be inclusive and fosters diverse discussions and viewpoints, and works +to improve those characteristics over time. A majority of the reports the +Code of Conduct Committee receives stem from incorrect understanding regarding +the development process and maintainers' roles, responsibilities, and their +right to make decisions on code acceptance. These are resolved through +clarification of the development process and the scope of the Code of Conduct. + +Unacceptable behaviors could interrupt respectful collaboration for a short +period of time and negatively impact the health of the community longer term. +Unacceptable behaviors often get resolved when individuals acknowledge their +behavior and make amends for it in the setting the violation has taken place. + +The Code of Conduct Committee receives reports about unacceptable behaviors +when they don't get resolved through community discussions. The Code of +Conduct committee takes measures to restore productive and respectful +collaboration when an unacceptable behavior has negatively impacted that +relationship. + +The Code of Conduct Committee has the obligation to keep the reports and +reporters' information private. Reports could come from injured parties +and community members who are observers of unacceptable behaviors. The +Code of Conduct Committee has the responsibility to investigate and resolve +these reports, working with all involved parties. + +The Code of Conduct Committee works with the individual to bring about +change in their understanding of the importance to repair the damage caused +by their behavior to the injured party and the long term negative impact +on the community. + +The goal is to reach a resolution which is agreeable to all parties. If +working with the individual fails to bring about the desired outcome, the +Code of Conduct Committee will evaluate other measures such as seeking +public apology to repair the damage. + +Seek public apology for the violation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The Code of Conduct Committee publicly calls out the behavior in the +setting in which the violation has taken place, seeking public apology +for the violation. + +A public apology for the violation is the first step towards rebuilding +the trust. Trust is essential for the continued success and health of the +community which operates on trust and respect. + +Remedial measures if there is no public apology for the violation +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +The Code of Conduct Committee determines the next course of action to restore +the healthy collaboration by recommending remedial measure(s) to the TAB for +approval. + +- Ban violator from participating in the kernel development process for + a period of up to a full kernel development cycle. The Code of Conduct + Committee could require public apology as a condition for lifting the + ban. + +The scope of the ban for a period of time could include: + + a. denying patch contributions and pull requests + b. pausing collaboration with the violator by ignoring their + contributions and/or blocking their email account(s) + c. restricting their ability to communicate via kernel.org platforms, + such as mailing lists and social media sites + +Once the TAB approves one or more of the measures outlined in the scope of +the ban by a two-thirds vote, the Code of Conduct Committee will enforce +the TAB approved measure(s) in collaboration with the community, maintainers, +sub-maintainers, and kernel.org administrators. + +The Code of Conduct Committee is mindful of the negative impact of seeking +public apology and instituting ban could have on individuals. It is also +mindful of the longer term harm to the community that could result from +not taking action when such serious public violations occur. + +The effectiveness of the remedial measure(s) approved by the TAB depends +on the trust and cooperation from the community, maintainers, sub-maintainers, +and kernel.org administrators in enforcing them. + +The Code of Conduct Committee sincerely hopes that unacceptable behaviors +that require seeking public apologies continue to be exceedingly rare +occurrences in the future. diff --git a/Documentation/process/debugging/driver_development_debugging_guide.rst b/Documentation/process/debugging/driver_development_debugging_guide.rst new file mode 100644 index 000000000000..aef204094205 --- /dev/null +++ b/Documentation/process/debugging/driver_development_debugging_guide.rst @@ -0,0 +1,223 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================================== +Debugging advice for driver development +======================================== + +This document serves as a general starting point and lookup for debugging +device drivers. +While this guide focuses on debugging that requires re-compiling the +module/kernel, the :doc:`userspace debugging guide +</process/debugging/userspace_debugging_guide>` will guide +you through tools like dynamic debug, ftrace and other tools useful for +debugging issues and behavior. +For general debugging advice, see the :doc:`general advice document +</process/debugging/index>`. + +.. contents:: + :depth: 3 + +The following sections show you the available tools. + +printk() & friends +------------------ + +These are derivatives of printf() with varying destinations and support for +being dynamically turned on or off, or lack thereof. + +Simple printk() +~~~~~~~~~~~~~~~ + +The classic, can be used to great effect for quick and dirty development +of new modules or to extract arbitrary necessary data for troubleshooting. + +Prerequisite: ``CONFIG_PRINTK`` (usually enabled by default) + +**Pros**: + +- No need to learn anything, simple to use +- Easy to modify exactly to your needs (formatting of the data (See: + :doc:`/core-api/printk-formats`), visibility in the log) +- Can cause delays in the execution of the code (beneficial to confirm whether + timing is a factor) + +**Cons**: + +- Requires rebuilding the kernel/module +- Can cause delays in the execution of the code (which can cause issues to be + not reproducible) + +For the full documentation see :doc:`/core-api/printk-basics` + +Trace_printk +~~~~~~~~~~~~ + +Prerequisite: ``CONFIG_DYNAMIC_FTRACE`` & ``#include <linux/ftrace.h>`` + +It is a tiny bit less comfortable to use than printk(), because you will have +to read the messages from the trace file (See: :ref:`read_ftrace_log` +instead of from the kernel log, but very useful when printk() adds unwanted +delays into the code execution, causing issues to be flaky or hidden.) + +If the processing of this still causes timing issues then you can try +trace_puts(). + +For the full Documentation see trace_printk() + +dev_dbg +~~~~~~~ + +Print statement, which can be targeted by +:ref:`process/debugging/userspace_debugging_guide:dynamic debug` that contains +additional information about the device used within the context. + +**When is it appropriate to leave a debug print in the code?** + +Permanent debug statements have to be useful for a developer to troubleshoot +driver misbehavior. Judging that is a bit more of an art than a science, but +some guidelines are in the :ref:`Coding style guidelines +<process/coding-style:13) printing kernel messages>`. In almost all cases the +debug statements shouldn't be upstreamed, as a working driver is supposed to be +silent. + +Custom printk +~~~~~~~~~~~~~ + +Example:: + + #define core_dbg(fmt, arg...) do { \ + if (core_debug) \ + printk(KERN_DEBUG pr_fmt("core: " fmt), ## arg); \ + } while (0) + +**When should you do this?** + +It is better to just use a pr_debug(), which can later be turned on/off with +dynamic debug. Additionally, a lot of drivers activate these prints via a +variable like ``core_debug`` set by a module parameter. However, Module +parameters `are not recommended anymore +<https://lore.kernel.org/all/2024032757-surcharge-grime-d3dd@gregkh>`_. + +Ftrace +------ + +Creating a custom Ftrace tracepoint +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A tracepoint adds a hook into your code that will be called and logged when the +tracepoint is enabled. This can be used, for example, to trace hitting a +conditional branch or to dump the internal state at specific points of the code +flow during a debugging session. + +Here is a basic description of :ref:`how to implement new tracepoints +<trace/tracepoints:usage>`. + +For the full event tracing documentation see :doc:`/trace/events` + +For the full Ftrace documentation see :doc:`/trace/ftrace` + +DebugFS +------- + +Prerequisite: ``CONFIG_DEBUG_FS` & `#include <linux/debugfs.h>`` + +DebugFS differs from the other approaches of debugging, as it doesn't write +messages to the kernel log nor add traces to the code. Instead it allows the +developer to handle a set of files. +With these files you can either store values of variables or make +register/memory dumps or you can make these files writable and modify +values/settings in the driver. + +Possible use-cases among others: + +- Store register values +- Keep track of variables +- Store errors +- Store settings +- Toggle a setting like debug on/off +- Error injection + +This is especially useful, when the size of a data dump would be hard to digest +as part of the general kernel log (for example when dumping raw bitstream data) +or when you are not interested in all the values all the time, but with the +possibility to inspect them. + +The general idea is: + +- Create a directory during probe (``struct dentry *parent = + debugfs_create_dir("my_driver", NULL);``) +- Create a file (``debugfs_create_u32("my_value", 444, parent, &my_variable);``) + + - In this example the file is found in + ``/sys/kernel/debug/my_driver/my_value`` (with read permissions for + user/group/all) + - any read of the file will return the current contents of the variable + ``my_variable`` + +- Clean up the directory when removing the device + (``debugfs_remove_recursive(parent);``) + +For the full documentation see :doc:`/filesystems/debugfs`. + +KASAN, UBSAN, lockdep and other error checkers +---------------------------------------------- + +KASAN (Kernel Address Sanitizer) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Prerequisite: ``CONFIG_KASAN`` + +KASAN is a dynamic memory error detector that helps to find use-after-free and +out-of-bounds bugs. It uses compile-time instrumentation to check every memory +access. + +For the full documentation see :doc:`/dev-tools/kasan`. + +UBSAN (Undefined Behavior Sanitizer) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Prerequisite: ``CONFIG_UBSAN`` + +UBSAN relies on compiler instrumentation and runtime checks to detect undefined +behavior. It is designed to find a variety of issues, including signed integer +overflow, array index out of bounds, and more. + +For the full documentation see :doc:`/dev-tools/ubsan` + +lockdep (Lock Dependency Validator) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Prerequisite: ``CONFIG_DEBUG_LOCKDEP`` + +lockdep is a runtime lock dependency validator that detects potential deadlocks +and other locking-related issues in the kernel. +It tracks lock acquisitions and releases, building a dependency graph that is +analyzed for potential deadlocks. +lockdep is especially useful for validating the correctness of lock ordering in +the kernel. + +PSI (Pressure stall information tracking) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Prerequisite: ``CONFIG_PSI`` + +PSI is a measurement tool to identify excessive overcommits on hardware +resources, that can cause performance disruptions or even OOM kills. + +device coredump +--------------- + +Prerequisite: ``#include <linux/devcoredump.h>`` + +Provides the infrastructure for a driver to provide arbitrary data to userland. +It is most often used in conjunction with udev or similar userland application +to listen for kernel uevents, which indicate that the dump is ready. Udev has +rules to copy that file somewhere for long-term storage and analysis, as by +default, the data for the dump is automatically cleaned up after 5 minutes. +That data is analyzed with driver-specific tools or GDB. + +You can find an example implementation at: +`drivers/media/platform/qcom/venus/core.c +<https://elixir.bootlin.com/linux/v6.11.6/source/drivers/media/platform/qcom/venus/core.c#L30>`__ + +**Copyright** ©2024 : Collabora diff --git a/Documentation/process/debugging/index.rst b/Documentation/process/debugging/index.rst new file mode 100644 index 000000000000..f6e4a00dfee3 --- /dev/null +++ b/Documentation/process/debugging/index.rst @@ -0,0 +1,78 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================ +Debugging advice for Linux Kernel developers +============================================ + +general guides +-------------- + +.. toctree:: + :maxdepth: 1 + + driver_development_debugging_guide + userspace_debugging_guide + +.. only:: subproject and html + +subsystem specific guides +------------------------- + +.. toctree:: + :maxdepth: 1 + + media_specific_debugging_guide + +.. only:: subproject and html + + Indices + ======= + + * :ref:`genindex` + +General debugging advice +======================== + +Depending on the issue, a different set of tools is available to track down the +problem or even to realize whether there is one in the first place. + +As a first step you have to figure out what kind of issue you want to debug. +Depending on the answer, your methodology and choice of tools may vary. + +Do I need to debug with limited access? +--------------------------------------- + +Do you have limited access to the machine or are you unable to stop the running +execution? + +In this case your debugging capability depends on built-in debugging support of +provided distribution kernel. +The :doc:`/process/debugging/userspace_debugging_guide` provides a brief +overview over a range of possible debugging tools in that situation. You can +check the capability of your kernel, in most cases, by looking into config file +within the /boot directory. + +Do I have root access to the system? +------------------------------------ + +Are you easily able to replace the module in question or to install a new +kernel? + +In that case your range of available tools is a lot bigger, you can find the +tools in the :doc:`/process/debugging/driver_development_debugging_guide`. + +Is timing a factor? +------------------- + +It is important to understand if the problem you want to debug manifests itself +consistently (i.e. given a set of inputs you always get the same, incorrect +output), or inconsistently. If it manifests itself inconsistently, some timing +factor might be at play. If inserting delays into the code does change the +behavior, then quite likely timing is a factor. + +When timing does alter the outcome of the code execution using a simple +printk() for debugging purposes may not work, a similar alternative is to use +trace_printk() , which logs the debug messages to the trace file instead of the +kernel log. + +**Copyright** ©2024 : Collabora diff --git a/Documentation/process/debugging/media_specific_debugging_guide.rst b/Documentation/process/debugging/media_specific_debugging_guide.rst new file mode 100644 index 000000000000..c5a93bafaf67 --- /dev/null +++ b/Documentation/process/debugging/media_specific_debugging_guide.rst @@ -0,0 +1,180 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================================ +Debugging and tracing in the media subsystem +============================================ + +This document serves as a starting point and lookup for debugging device +drivers in the media subsystem and to debug these drivers from userspace. + +.. contents:: + :depth: 3 + +General debugging advice +------------------------ + +For general advice see the :doc:`general advice document +</process/debugging/index>`. + +The following sections show you some of the available tools. + +dev_debug module parameter +-------------------------- + +Every video device provides a ``dev_debug`` parameter, which allows to get +further insights into the IOCTLs in the background.:: + + # cat /sys/class/video4linux/video3/name + rkvdec + # echo 0xff > /sys/class/video4linux/video3/dev_debug + # dmesg -wH + [...] videodev: v4l2_open: video3: open (0) + [ +0.000036] video3: VIDIOC_QUERYCAP: driver=rkvdec, card=rkvdec, + bus=platform:rkvdec, version=0x00060900, capabilities=0x84204000, + device_caps=0x04204000 + +For the full documentation see :ref:`driver-api/media/v4l2-dev:video device +debugging` + +dev_dbg() / v4l2_dbg() +---------------------- + +Two debug print statements, which are specific for devices and for the v4l2 +subsystem, avoid adding these to your final submission unless they have +long-term value for investigations. + +For a general overview please see the +:ref:`process/debugging/driver_development_debugging_guide:printk() & friends` +guide. + +- Difference between both? + + - v4l2_dbg() utilizes v4l2_printk() under the hood, which further uses + printk() directly, thus it cannot be targeted by dynamic debug + - dev_dbg() can be targeted by dynamic debug + - v4l2_dbg() has a more specific prefix format for the media subsystem, while + dev_dbg only highlights the driver name and the location of the log + +Dynamic debug +------------- + +A method to trim down the debug output to your needs. + +For general advice see the +:ref:`process/debugging/userspace_debugging_guide:dynamic debug` guide. + +Here is one example, that enables all available pr_debug()'s within the file:: + + $ alias ddcmd='echo $* > /proc/dynamic_debug/control' + $ ddcmd '-p; file v4l2-h264.c +p' + $ grep =p /proc/dynamic_debug/control + drivers/media/v4l2-core/v4l2-h264.c:372 [v4l2_h264]print_ref_list_b =p + "ref_pic_list_b%u (cur_poc %u%c) %s" + drivers/media/v4l2-core/v4l2-h264.c:333 [v4l2_h264]print_ref_list_p =p + "ref_pic_list_p (cur_poc %u%c) %s\n" + +Ftrace +------ + +An internal kernel tracer that can trace static predefined events, function +calls, etc. Very useful for debugging problems without changing the kernel and +understanding the behavior of subsystems. + +For general advice see the +:ref:`process/debugging/userspace_debugging_guide:ftrace` guide. + +DebugFS +------- + +This tool allows you to dump or modify internal values of your driver to files +in a custom filesystem. + +For general advice see the +:ref:`process/debugging/driver_development_debugging_guide:debugfs` guide. + +Perf & alternatives +------------------- + +Tools to measure the various stats on a running system to diagnose issues. + +For general advice see the +:ref:`process/debugging/userspace_debugging_guide:perf & alternatives` guide. + +Example for media devices: + +Gather statistics data for a decoding job: (This example is on a RK3399 SoC +with the rkvdec codec driver using the `fluster test suite +<https://github.com/fluendo/fluster>`__):: + + perf stat -d python3 fluster.py run -d GStreamer-H.264-V4L2SL-Gst1.0 -ts + JVT-AVC_V1 -tv AUD_MW_E -j1 + ... + Performance counter stats for 'python3 fluster.py run -d + GStreamer-H.264-V4L2SL-Gst1.0 -ts JVT-AVC_V1 -tv AUD_MW_E -j1 -v': + + 7794.23 msec task-clock:u # 0.697 CPUs utilized + 0 context-switches:u # 0.000 /sec + 0 cpu-migrations:u # 0.000 /sec + 11901 page-faults:u # 1.527 K/sec + 882671556 cycles:u # 0.113 GHz (95.79%) + 711708695 instructions:u # 0.81 insn per cycle (95.79%) + 10581935 branches:u # 1.358 M/sec (15.13%) + 6871144 branch-misses:u # 64.93% of all branches (95.79%) + 281716547 L1-dcache-loads:u # 36.144 M/sec (95.79%) + 9019581 L1-dcache-load-misses:u # 3.20% of all L1-dcache accesses (95.79%) + <not supported> LLC-loads:u + <not supported> LLC-load-misses:u + + 11.180830431 seconds time elapsed + + 1.502318000 seconds user + 6.377221000 seconds sys + +The availability of events and metrics depends on the system you are running. + +Error checking & panic analysis +------------------------------- + +Various Kernel configuration options to enhance error detection of the Linux +Kernel with the cost of lowering performance. + +For general advice see the +:ref:`process/debugging/driver_development_debugging_guide:kasan, ubsan, +lockdep and other error checkers` guide. + +Driver verification with v4l2-compliance +---------------------------------------- + +To verify, that a driver adheres to the v4l2 API, the tool v4l2-compliance is +used, which is part of the `v4l_utils +<https://git.linuxtv.org/v4l-utils.git>`__, a suite of userspace tools to work +with the media subsystem. + +To see the detailed media topology (and check it) use:: + + v4l2-compliance -M /dev/mediaX --verbose + +You can also run a full compliance check for all devices referenced in the +media topology with:: + + v4l2-compliance -m /dev/mediaX + +Debugging problems with receiving video +--------------------------------------- + +Implementing vidioc_log_status in the driver: this can log the current status +to the kernel log. It's called by v4l2-ctl --log-status. Very useful for +debugging problems with receiving video (TV/S-Video/HDMI/etc) since the video +signal is external (so unpredictable). Less useful with camera sensor inputs +since you have control over what the camera sensor does. + +Usually you can just assign the default:: + + .vidioc_log_status = v4l2_ctrl_log_status, + +But you can also create your own callback, to create a custom status log. + +You can find an example in the cobalt driver +(`drivers/media/pci/cobalt/cobalt-v4l2.c <https://elixir.bootlin.com/linux/v6.11.6/source/drivers/media/pci/cobalt/cobalt-v4l2.c#L567>`__). + +**Copyright** ©2024 : Collabora diff --git a/Documentation/process/debugging/userspace_debugging_guide.rst b/Documentation/process/debugging/userspace_debugging_guide.rst new file mode 100644 index 000000000000..db7396261e07 --- /dev/null +++ b/Documentation/process/debugging/userspace_debugging_guide.rst @@ -0,0 +1,280 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================== +Userspace debugging advice +========================== + +This document provides a brief overview of common tools to debug the Linux +Kernel from userspace. +For debugging advice aimed at driver developers go :doc:`here +</process/debugging/driver_development_debugging_guide>`. +For general debugging advice, see :doc:`general advice document +</process/debugging/index>`. + +.. contents:: + :depth: 3 + +The following sections show you the available tools. + +Dynamic debug +------------- + +Mechanism to filter what ends up in the kernel log by dis-/en-abling log +messages. + +Prerequisite: ``CONFIG_DYNAMIC_DEBUG`` + +Dynamic debug is only able to target: + +- pr_debug() +- dev_dbg() +- print_hex_dump_debug() +- print_hex_dump_bytes() + +Therefore the usability of this tool is, as of now, quite limited as there is +no uniform rule for adding debug prints to the codebase, resulting in a variety +of ways these prints are implemented. + +Also, note that most debug statements are implemented as a variation of +dprintk(), which have to be activated via a parameter in respective module, +dynamic debug is unable to do that step for you. + +Here is one example, that enables all available pr_debug()'s within the file:: + + $ alias ddcmd='echo $* > /proc/dynamic_debug/control' + $ ddcmd '-p; file v4l2-h264.c +p' + $ grep =p /proc/dynamic_debug/control + drivers/media/v4l2-core/v4l2-h264.c:372 [v4l2_h264]print_ref_list_b =p + "ref_pic_list_b%u (cur_poc %u%c) %s" + drivers/media/v4l2-core/v4l2-h264.c:333 [v4l2_h264]print_ref_list_p =p + "ref_pic_list_p (cur_poc %u%c) %s\n" + +**When should you use this over Ftrace ?** + +- When the code contains one of the valid print statements (see above) or when + you have added multiple pr_debug() statements during development +- When timing is not an issue, meaning if multiple pr_debug() statements in + the code won't cause delays +- When you care more about receiving specific log messages than tracing the + pattern of how a function is called + +For the full documentation see :doc:`/admin-guide/dynamic-debug-howto` + +Ftrace +------ + +Prerequisite: ``CONFIG_DYNAMIC_FTRACE`` + +This tool uses the tracefs file system for the control files and output files. +That file system will be mounted as a ``tracing`` directory, which can be found +in either ``/sys/kernel/`` or ``/sys/debug/kernel/``. + +Some of the most important operations for debugging are: + +- You can perform a function trace by adding a function name to the + ``set_ftrace_filter`` file (which accepts any function name found within the + ``available_filter_functions`` file) or you can specifically disable certain + functions by adding their names to the ``set_ftrace_notrace`` file (more info + at: :ref:`trace/ftrace:dynamic ftrace`). +- In order to find out where calls originate from you can activate the + ``func_stack_trace`` option under ``options/func_stack_trace``. +- Tracing the children of a function call and showing the return values are + possible by adding the desired function in the ``set_graph_function`` file + (requires config ``FUNCTION_GRAPH_RETVAL``); more info at + :ref:`trace/ftrace:dynamic ftrace with the function graph tracer`. + +For the full Ftrace documentation see :doc:`/trace/ftrace` + +Or you could also trace for specific events by :ref:`using event tracing +<trace/events:2. using event tracing>`, which can be defined as described here: +:ref:`Creating a custom Ftrace tracepoint +<process/debugging/driver_development_debugging_guide:ftrace>`. + +For the full Ftrace event tracing documentation see :doc:`/trace/events` + +.. _read_ftrace_log: + +Reading the ftrace log +~~~~~~~~~~~~~~~~~~~~~~ + +The ``trace`` file can be read just like any other file (``cat``, ``tail``, +``head``, ``vim``, etc.), the size of the file is limited by the +``buffer_size_kb`` (``echo 1000 > buffer_size_kb``). The +:ref:`trace/ftrace:trace_pipe` will behave similarly to the ``trace`` file, but +whenever you read from the file the content is consumed. + +Kernelshark +~~~~~~~~~~~ + +A GUI interface to visualize the traces as a graph and list view from the +output of the `trace-cmd +<https://git.kernel.org/pub/scm/utils/trace-cmd/trace-cmd.git/>`__ application. + +For the full documentation see `<https://kernelshark.org/Documentation.html>`__ + +Perf & alternatives +------------------- + +The tools mentioned above provide ways to inspect kernel code, results, +variable values, etc. Sometimes you have to find out first where to look and +for those cases, a box of performance tracking tools can help you to frame the +issue. + +Why should you do a performance analysis? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A performance analysis is a good first step when among other reasons: + +- you cannot define the issue +- you do not know where it occurs +- the running system should not be interrupted or it is a remote system, where + you cannot install a new module/kernel + +How to do a simple analysis with linux tools? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +For the start of a performance analysis, you can start with the usual tools +like: + +- ``top`` / ``htop`` / ``atop`` (*get an overview of the system load, see + spikes on specific processes*) +- ``mpstat -P ALL`` (*look at the load distribution among CPUs*) +- ``iostat -x`` (*observe input and output devices utilization and performance*) +- ``vmstat`` (*overview of memory usage on the system*) +- ``pidstat`` (*similar to* ``vmstat`` *but per process, to dial it down to the + target*) +- ``strace -tp $PID`` (*once you know the process, you can figure out how it + communicates with the Kernel*) + +These should help to narrow down the areas to look at sufficiently. + +Diving deeper with perf +~~~~~~~~~~~~~~~~~~~~~~~ + +The **perf** tool provides a series of metrics and events to further dial down +on issues. + +Prerequisite: build or install perf on your system + +Gather statistics data for finding all files starting with ``gcc`` in ``/usr``:: + + # perf stat -d find /usr -name 'gcc*' | wc -l + + Performance counter stats for 'find /usr -name gcc*': + + 1277.81 msec task-clock # 0.997 CPUs utilized + 9 context-switches # 7.043 /sec + 1 cpu-migrations # 0.783 /sec + 704 page-faults # 550.943 /sec + 766548897 cycles # 0.600 GHz (97.15%) + 798285467 instructions # 1.04 insn per cycle (97.15%) + 57582731 branches # 45.064 M/sec (2.85%) + 3842573 branch-misses # 6.67% of all branches (97.15%) + 281616097 L1-dcache-loads # 220.390 M/sec (97.15%) + 4220975 L1-dcache-load-misses # 1.50% of all L1-dcache accesses (97.15%) + <not supported> LLC-loads + <not supported> LLC-load-misses + + 1.281746009 seconds time elapsed + + 0.508796000 seconds user + 0.773209000 seconds sys + + + 52 + +The availability of events and metrics depends on the system you are running. + +For the full documentation see +`<https://perf.wiki.kernel.org/index.php/Main_Page>`__ + +Perfetto +~~~~~~~~ + +A set of tools to measure and analyze how well applications and systems perform. +You can use it to: + +* identify bottlenecks +* optimize code +* make software run faster and more efficiently. + +**What is the difference between perfetto and perf?** + +* perf is tool as part of and specialized for the Linux Kernel and has CLI user + interface. +* perfetto cross-platform performance analysis stack, has extended + functionality into userspace and provides a WEB user interface. + +For the full documentation see `<https://perfetto.dev/docs/>`__ + +Kernel panic analysis tools +--------------------------- + + To capture the crash dump please use ``Kdump`` & ``Kexec``. Below you can find + some advice for analysing the data. + + For the full documentation see the :doc:`/admin-guide/kdump/kdump` + + In order to find the corresponding line in the code you can use `faddr2line + <https://elixir.bootlin.com/linux/v6.11.6/source/scripts/faddr2line>`__; note + that you need to enable ``CONFIG_DEBUG_INFO`` for that to work. + + An alternative to using ``faddr2line`` is the use of ``objdump`` (and its + derivatives for the different platforms like ``aarch64-linux-gnu-objdump``). + Take this line as an example: + + ``[ +0.000240] rkvdec_device_run+0x50/0x138 [rockchip_vdec]``. + + We can find the corresponding line of code by executing:: + + aarch64-linux-gnu-objdump -dS drivers/staging/media/rkvdec/rockchip-vdec.ko | grep rkvdec_device_run\>: -A 40 + 0000000000000ac8 <rkvdec_device_run>: + ac8: d503201f nop + acc: d503201f nop + { + ad0: d503233f paciasp + ad4: a9bd7bfd stp x29, x30, [sp, #-48]! + ad8: 910003fd mov x29, sp + adc: a90153f3 stp x19, x20, [sp, #16] + ae0: a9025bf5 stp x21, x22, [sp, #32] + const struct rkvdec_coded_fmt_desc *desc = ctx->coded_fmt_desc; + ae4: f9411814 ldr x20, [x0, #560] + struct rkvdec_dev *rkvdec = ctx->dev; + ae8: f9418015 ldr x21, [x0, #768] + if (WARN_ON(!desc)) + aec: b4000654 cbz x20, bb4 <rkvdec_device_run+0xec> + ret = pm_runtime_resume_and_get(rkvdec->dev); + af0: f943d2b6 ldr x22, [x21, #1952] + ret = __pm_runtime_resume(dev, RPM_GET_PUT); + af4: aa0003f3 mov x19, x0 + af8: 52800081 mov w1, #0x4 // #4 + afc: aa1603e0 mov x0, x22 + b00: 94000000 bl 0 <__pm_runtime_resume> + if (ret < 0) { + b04: 37f80340 tbnz w0, #31, b6c <rkvdec_device_run+0xa4> + dev_warn(rkvdec->dev, "Not good\n"); + b08: f943d2a0 ldr x0, [x21, #1952] + b0c: 90000001 adrp x1, 0 <rkvdec_try_ctrl-0x8> + b10: 91000021 add x1, x1, #0x0 + b14: 94000000 bl 0 <_dev_warn> + *bad = 1; + b18: d2800001 mov x1, #0x0 // #0 + ... + + Meaning, in this line from the crash dump:: + + [ +0.000240] rkvdec_device_run+0x50/0x138 [rockchip_vdec] + + I can take the ``0x50`` as offset, which I have to add to the base address + of the corresponding function, which I find in this line:: + + 0000000000000ac8 <rkvdec_device_run>: + + The result of ``0xac8 + 0x50 = 0xb18`` + And when I search for that address within the function I get the + following line:: + + *bad = 1; + b18: d2800001 mov x1, #0x0 + +**Copyright** ©2024 : Collabora diff --git a/Documentation/process/index.rst b/Documentation/process/index.rst index 6455eba3ef0c..aa12f2660194 100644 --- a/Documentation/process/index.rst +++ b/Documentation/process/index.rst @@ -72,13 +72,15 @@ beyond). Dealing with bugs ----------------- -Bugs are a fact of life; it is important that we handle them properly. -The documents below describe our policies around the handling of a couple -of special classes of bugs: regressions and security problems. +Bugs are a fact of life; it is important that we handle them properly. The +documents below provide general advice about debugging and describe our +policies around the handling of a couple of special classes of bugs: +regressions and security problems. .. toctree:: :maxdepth: 1 + debugging/index handling-regressions security-bugs cve diff --git a/Documentation/process/kernel-docs.rst b/Documentation/process/kernel-docs.rst index 55552ec4b043..3b5b5983fea8 100644 --- a/Documentation/process/kernel-docs.rst +++ b/Documentation/process/kernel-docs.rst @@ -72,17 +72,6 @@ On-line docs programming. Lots of examples. Currently the new version is being actively maintained at https://github.com/sysprog21/lkmpg. - * Title: **Rust for Linux** - - :Author: various - :URL: https://rust-for-linux.com/ - :Date: rolling version - :Keywords: glossary, terms, linux-kernel. - :Description: From the website: "Rust for Linux is the project adding - support for the Rust language to the Linux kernel. This website is - intended as a hub of links, documentation and resources related to - the project". - Published books --------------- @@ -220,6 +209,158 @@ Miscellaneous other original research and content related to Linux and software development. +Rust +---- + + * Title: **Rust for Linux** + + :Author: various + :URL: https://rust-for-linux.com/ + :Date: rolling version + :Keywords: glossary, terms, linux-kernel, rust. + :Description: From the website: "Rust for Linux is the project adding + support for the Rust language to the Linux kernel. This website is + intended as a hub of links, documentation and resources related to + the project". + + * Title: **Learn Rust the Dangerous Way** + + :Author: Cliff L. Biffle + :URL: https://cliffle.com/p/dangerust/ + :Date: Accessed Sep 11 2024 + :Keywords: rust, blog. + :Description: From the website: "LRtDW is a series of articles + putting Rust features in context for low-level C programmers who + maybe don’t have a formal CS background — the sort of people who + work on firmware, game engines, OS kernels, and the like. + Basically, people like me.". It illustrates line-by-line + conversions from C to Rust. + + * Title: **The Rust Book** + + :Author: Steve Klabnik and Carol Nichols, with contributions from the + Rust community + :URL: https://doc.rust-lang.org/book/ + :Date: Accessed Sep 11 2024 + :Keywords: rust, book. + :Description: From the website: "This book fully embraces the + potential of Rust to empower its users. It’s a friendly and + approachable text intended to help you level up not just your + knowledge of Rust, but also your reach and confidence as a + programmer in general. So dive in, get ready to learn—and welcome + to the Rust community!". + + * Title: **Rust for the Polyglot Programmer** + + :Author: Ian Jackson + :URL: https://www.chiark.greenend.org.uk/~ianmdlvl/rust-polyglot/index.html + :Date: December 2022 + :Keywords: rust, blog, tooling. + :Description: From the website: "There are many guides and + introductions to Rust. This one is something different: it is + intended for the experienced programmer who already knows many + other programming languages. I try to be comprehensive enough to be + a starting point for any area of Rust, but to avoid going into too + much detail except where things are not as you might expect. Also + this guide is not entirely free of opinion, including + recommendations of libraries (crates), tooling, etc.". + + * Title: **Fasterthanli.me** + + :Author: Amos Wenger + :URL: https://fasterthanli.me/ + :Date: Accessed Sep 11 2024 + :Keywords: rust, blog, news. + :Description: From the website: "I make articles and videos about how + computers work. My content is long-form, didactic and exploratory + — and often an excuse to teach Rust!". + + * Title: **Comprehensive Rust** + + :Author: Android team at Google + :URL: https://google.github.io/comprehensive-rust/ + :Date: Accessed Sep 13 2024 + :Keywords: rust, blog. + :Description: From the website: "The course covers the full spectrum + of Rust, from basic syntax to advanced topics like generics and + error handling". + + * Title: **The Embedded Rust Book** + + :Author: Multiple contributors, mostly Jorge Aparicio + :URL: https://docs.rust-embedded.org/book/ + :Date: Accessed Sep 13 2024 + :Keywords: rust, blog. + :Description: From the website: "An introductory book about using + the Rust Programming Language on "Bare Metal" embedded systems, + such as Microcontrollers". + + * Title: **Experiment: Improving the Rust Book** + + :Author: Cognitive Engineering Lab at Brown University + :URL: https://rust-book.cs.brown.edu/ + :Date: Accessed Sep 22 2024 + :Keywords: rust, blog. + :Description: From the website: "The goal of this experiment is to + evaluate and improve the content of the Rust Book to help people + learn Rust more effectively.". + + * Title: **New Rustacean** (podcast) + + :Author: Chris Krycho + :URL: https://newrustacean.com/ + :Date: Accessed Sep 22 2024 + :Keywords: rust, podcast. + :Description: From the website: "This is a podcast about learning + the programming language Rust—from scratch! Apart from this spiffy + landing page, all the site content is built with Rust's own + documentation tools.". + + * Title: **Opsem-team** (repository) + + :Author: Operational semantics team + :URL: https://github.com/rust-lang/opsem-team/tree/main + :Date: Accessed Sep 22 2024 + :Keywords: rust, repository. + :Description: From the README: "The opsem team is the successor of + the unsafe-code-guidelines working group and responsible for + answering many of the difficult questions about the semantics of + unsafe Rust". + + * Title: **You Can't Spell Trust Without Rust** + + :Author: Alexis Beingessner + :URL: https://repository.library.carleton.ca/downloads/1j92g820w?locale=en + :Date: 2015 + :Keywords: rust, master, thesis. + :Description: This thesis focuses on Rust's ownership system, which + ensures memory safety by controlling data manipulation and + lifetime, while also highlighting its limitations and comparing it + to similar systems in Cyclone and C++. + + * Name: **Linux Plumbers (LPC) 2024 Rust presentations** + + :Title: Rust microconference + :URL: https://lpc.events/event/18/sessions/186/#20240918 + :Title: Rust for Linux + :URL: https://lpc.events/event/18/contributions/1912/ + :Title: Journey of a C kernel engineer starting a Rust driver project + :URL: https://lpc.events/event/18/contributions/1911/ + :Title: Crafting a Linux kernel scheduler that runs in user-space + using Rust + :URL: https://lpc.events/event/18/contributions/1723/ + :Title: openHCL: A Linux and Rust based paravisor + :URL: https://lpc.events/event/18/contributions/1956/ + :Keywords: rust, lpc, presentations. + :Description: A number of LPC talks related to Rust. + + * Name: **The Rustacean Station Podcast** + + :URL: https://rustacean-station.org/ + :Keywords: rust, podcasts. + :Description: A community project for creating podcast content for + the Rust programming language. + ------- This document was originally based on: diff --git a/Documentation/process/license-rules.rst b/Documentation/process/license-rules.rst index 2ef44ada3f11..59a7832df7d0 100644 --- a/Documentation/process/license-rules.rst +++ b/Documentation/process/license-rules.rst @@ -471,14 +471,16 @@ _`MODULE_LICENSE` source files. "Proprietary" The module is under a proprietary license. - This string is solely for proprietary third - party modules and cannot be used for modules - which have their source code in the kernel - tree. Modules tagged that way are tainting - the kernel with the 'P' flag when loaded and - the kernel module loader refuses to link such - modules against symbols which are exported - with EXPORT_SYMBOL_GPL(). + "Proprietary" is to be understood only as + "The license is not compatible to GPLv2". + This string is solely for non-GPL2 compatible + third party modules and cannot be used for + modules which have their source code in the + kernel tree. Modules tagged that way are + tainting the kernel with the 'P' flag when + loaded and the kernel module loader refuses + to link such modules against symbols which + are exported with EXPORT_SYMBOL_GPL(). ============================= ============================================= diff --git a/Documentation/process/maintainer-tip.rst b/Documentation/process/maintainer-tip.rst index 349a27a53343..e374b67b3277 100644 --- a/Documentation/process/maintainer-tip.rst +++ b/Documentation/process/maintainer-tip.rst @@ -7,7 +7,7 @@ What is the tip tree? --------------------- The tip tree is a collection of several subsystems and areas of -development. The tip tree is both a direct development tree and a +development. The tip tree is both a direct development tree and an aggregation tree for several sub-maintainer trees. The tip tree gitweb URL is: https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git @@ -121,7 +121,7 @@ The tip tree preferred format for patch subject prefixes is prefix. 'git log path/to/file' should give you a reasonable hint in most cases. -The condensed patch description in the subject line should start with a +The condensed patch description in the subject line should start with an uppercase letter and should be written in imperative tone. |