mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
synced 2024-12-29 09:12:07 +00:00
A few late-arriving fixes, plus two more significant changes that were
*almost* ready at the beginning of the merge window:
- A new document on debugging techniques from Sebastian Fricke
- A clarification on MODULE_LICENSE terms meant to head off the sort of
confusion that led to the recent Tuxedo Computers mess.
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Merge tag 'docs-6.13-2' of git://git.lwn.net/linux
Pull more documentation updates from Jonathan Corbet:
"A few late-arriving fixes, plus two more significant changes that were
*almost* ready at the beginning of the merge window:
- A new document on debugging techniques from Sebastian Fricke
- A clarification on MODULE_LICENSE terms meant to head off the sort
of confusion that led to the recent Tuxedo Computers mess"
* tag 'docs-6.13-2' of git://git.lwn.net/linux:
docs: Add debugging guide for the media subsystem
docs: Add debugging section to process
docs/licensing: Clarify wording about "GPL" and "Proprietary"
docs: core-api/gfp_mask-from-fs-io: indicate that vmalloc supports GFP_NOFS/GFP_NOIO
Documentation: kernel-doc: enumerate identifier *type*s
Documentation: pwrseq: Fix trivial misspellings
Documentation: filesystems: update filename extensions
This commit is contained in:
Linus Torvalds
commit
e68ce9474a
@ -20,6 +20,11 @@ Documentation/driver-api/media/index.rst
|
||||
- for driver development information and Kernel APIs used by
|
||||
media devices;
|
||||
|
||||
Documentation/process/debugging/media_specific_debugging_guide.rst
|
||||
|
||||
- for advice about essential tools and techniques to debug drivers on this
|
||||
subsystem
|
||||
|
||||
.. toctree::
|
||||
:caption: Table of Contents
|
||||
:maxdepth: 2
|
||||
|
||||
@ -55,14 +55,16 @@ scope.
|
||||
What about __vmalloc(GFP_NOFS)
|
||||
==============================
|
||||
|
||||
vmalloc doesn't support GFP_NOFS semantic because there are hardcoded
|
||||
GFP_KERNEL allocations deep inside the allocator which are quite non-trivial
|
||||
to fix up. That means that calling ``vmalloc`` with GFP_NOFS/GFP_NOIO is
|
||||
almost always a bug. The good news is that the NOFS/NOIO semantic can be
|
||||
achieved by the scope API.
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||||
Since v5.17, and specifically after the commit 451769ebb7e79 ("mm/vmalloc:
|
||||
alloc GFP_NO{FS,IO} for vmalloc"), GFP_NOFS/GFP_NOIO are now supported in
|
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``[k]vmalloc`` by implicitly using scope API.
|
||||
|
||||
In earlier kernels ``vmalloc`` didn't support GFP_NOFS semantic because there
|
||||
were hardcoded GFP_KERNEL allocations deep inside the allocator. That means
|
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that calling ``vmalloc`` with GFP_NOFS/GFP_NOIO was almost always a bug.
|
||||
|
||||
In the ideal world, upper layers should already mark dangerous contexts
|
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and so no special care is required and vmalloc should be called without
|
||||
any problems. Sometimes if the context is not really clear or there are
|
||||
layering violations then the recommended way around that is to wrap ``vmalloc``
|
||||
by the scope API with a comment explaining the problem.
|
||||
and so no special care is required and ``vmalloc`` should be called without any
|
||||
problems. Sometimes if the context is not really clear or there are layering
|
||||
violations then the recommended way around that (on pre-v5.17 kernels) is to
|
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wrap ``vmalloc`` by the scope API with a comment explaining the problem.
|
||||
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@ -533,6 +533,7 @@ identifiers: *[ function/type ...]*
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||||
Include documentation for each *function* and *type* in *source*.
|
||||
If no *function* is specified, the documentation for all functions
|
||||
and types in the *source* will be included.
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||||
*type* can be a struct, union, enum, or typedef identifier.
|
||||
|
||||
Examples::
|
||||
|
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|
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@ -11,7 +11,7 @@ Introduction
|
||||
============
|
||||
|
||||
This framework is designed to abstract complex power-up sequences that are
|
||||
shared between multiple logical devices in the linux kernel.
|
||||
shared between multiple logical devices in the Linux kernel.
|
||||
|
||||
The intention is to allow consumers to obtain a power sequencing handle
|
||||
exposed by the power sequence provider and delegate the actual requesting and
|
||||
@ -25,7 +25,7 @@ The power sequencing API uses a number of terms specific to the subsystem:
|
||||
|
||||
Unit
|
||||
|
||||
A unit is a discreet chunk of a power sequence. For instance one unit may
|
||||
A unit is a discrete chunk of a power sequence. For instance one unit may
|
||||
enable a set of regulators, another may enable a specific GPIO. Units can
|
||||
define dependencies in the form of other units that must be enabled before
|
||||
it itself can be.
|
||||
@ -62,7 +62,7 @@ Provider interface
|
||||
The provider API is admittedly not nearly as straightforward as the one for
|
||||
consumers but it makes up for it in flexibility.
|
||||
|
||||
Each provider can logically split the power-up sequence into descrete chunks
|
||||
Each provider can logically split the power-up sequence into discrete chunks
|
||||
(units) and define their dependencies. They can then expose named targets that
|
||||
consumers may use as the final point in the sequence that they wish to reach.
|
||||
|
||||
@ -72,7 +72,7 @@ register with the pwrseq subsystem by calling pwrseq_device_register().
|
||||
Dynamic consumer matching
|
||||
-------------------------
|
||||
|
||||
The main difference between pwrseq and other linux kernel providers is the
|
||||
The main difference between pwrseq and other Linux kernel providers is the
|
||||
mechanism for dynamic matching of consumers and providers. Every power sequence
|
||||
provider driver must implement the `match()` callback and pass it to the pwrseq
|
||||
core when registering with the subsystems.
|
||||
|
||||
@ -442,7 +442,7 @@ which can be used to communicate directly with the autofs filesystem.
|
||||
It requires CAP_SYS_ADMIN for access.
|
||||
|
||||
The 'ioctl's that can be used on this device are described in a separate
|
||||
document `autofs-mount-control.txt`, and are summarised briefly here.
|
||||
document `autofs-mount-control.rst`, and are summarised briefly here.
|
||||
Each ioctl is passed a pointer to an `autofs_dev_ioctl` structure::
|
||||
|
||||
struct autofs_dev_ioctl {
|
||||
|
||||
@ -36,7 +36,7 @@ None
|
||||
Usage
|
||||
=====
|
||||
|
||||
If you're just interested in OCFS2, then please see ocfs2.txt. The
|
||||
If you're just interested in OCFS2, then please see ocfs2.rst. The
|
||||
rest of this document will be geared towards those who want to use
|
||||
dlmfs for easy to setup and easy to use clustered locking in
|
||||
userspace.
|
||||
|
||||
@ -16,7 +16,7 @@ btrfs filesystems. Like fscrypt, not too much filesystem-specific
|
||||
code is needed to support fs-verity.
|
||||
|
||||
fs-verity is similar to `dm-verity
|
||||
<https://www.kernel.org/doc/Documentation/device-mapper/verity.txt>`_
|
||||
<https://www.kernel.org/doc/Documentation/admin-guide/device-mapper/verity.rst>`_
|
||||
but works on files rather than block devices. On regular files on
|
||||
filesystems supporting fs-verity, userspace can execute an ioctl that
|
||||
causes the filesystem to build a Merkle tree for the file and persist
|
||||
|
||||
@ -531,7 +531,7 @@ this retry process in the next article.
|
||||
Automount points are locations in the filesystem where an attempt to
|
||||
lookup a name can trigger changes to how that lookup should be
|
||||
handled, in particular by mounting a filesystem there. These are
|
||||
covered in greater detail in autofs.txt in the Linux documentation
|
||||
covered in greater detail in autofs.rst in the Linux documentation
|
||||
tree, but a few notes specifically related to path lookup are in order
|
||||
here.
|
||||
|
||||
|
||||
@ -379,4 +379,4 @@ Papers and other documentation on dcache locking
|
||||
|
||||
2. http://lse.sourceforge.net/locking/dcache/dcache.html
|
||||
|
||||
3. path-lookup.md in this directory.
|
||||
3. path-lookup.rst in this directory.
|
||||
|
||||
@ -315,7 +315,7 @@ the above threads) is:
|
||||
2) The cpio archive format chosen by the kernel is simpler and cleaner (and
|
||||
thus easier to create and parse) than any of the (literally dozens of)
|
||||
various tar archive formats. The complete initramfs archive format is
|
||||
explained in buffer-format.txt, created in usr/gen_init_cpio.c, and
|
||||
explained in buffer-format.rst, created in usr/gen_init_cpio.c, and
|
||||
extracted in init/initramfs.c. All three together come to less than 26k
|
||||
total of human-readable text.
|
||||
|
||||
|
||||
@ -587,7 +587,7 @@ Defined in ``include/linux/export.h``
|
||||
|
||||
Similar to :c:func:`EXPORT_SYMBOL()` except that the symbols
|
||||
exported by :c:func:`EXPORT_SYMBOL_GPL()` can only be seen by
|
||||
modules with a :c:func:`MODULE_LICENSE()` that specifies a GPL
|
||||
modules with a :c:func:`MODULE_LICENSE()` that specifies a GPLv2
|
||||
compatible license. It implies that the function is considered an
|
||||
internal implementation issue, and not really an interface. Some
|
||||
maintainers and developers may however require EXPORT_SYMBOL_GPL()
|
||||
|
||||
@ -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
|
||||
78
Documentation/process/debugging/index.rst
Normal file
78
Documentation/process/debugging/index.rst
Normal file
@ -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
|
||||
@ -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
|
||||
280
Documentation/process/debugging/userspace_debugging_guide.rst
Normal file
280
Documentation/process/debugging/userspace_debugging_guide.rst
Normal file
@ -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
|
||||
@ -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
|
||||
|
||||
@ -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().
|
||||
============================= =============================================
|
||||
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user