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Documentation: admin-guide: update bug-hunting.rst
Update Documentation/admin-guide/bug-hunting.rst: - add a small section on "Modules linked in" and their possible flags; - delete all references to ksymoops since it is no longer applicable; - fix spello, grammar, and punctuation; - note that get_maintainers.pl only provides recent patchers if it is run inside a git tree; - add mention of scripts/decode_stacktrace.sh; Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Cc: greg@wind.rmcc.com Link: https://lore.kernel.org/r/c629a9ef-3867-c3d1-f6c9-2c3b0e4ac68a@infradead.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Randy Dunlap
Jonathan Corbet
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@ -49,15 +49,19 @@ the issue, it may also contain the word **Oops**, as on this one::
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Despite being an **Oops** or some other sort of stack trace, the offended
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line is usually required to identify and handle the bug. Along this chapter,
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we'll refer to "Oops" for all kinds of stack traces that need to be analized.
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we'll refer to "Oops" for all kinds of stack traces that need to be analyzed.
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.. note::
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If the kernel is compiled with ``CONFIG_DEBUG_INFO``, you can enhance the
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quality of the stack trace by using file:`scripts/decode_stacktrace.sh`.
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Modules linked in
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-----------------
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Modules that are tainted or are being loaded or unloaded are marked with
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"(...)", where the taint flags are described in
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file:`Documentation/admin-guide/tainted-kernels.rst`, "being loaded" is
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annotated with "+", and "being unloaded" is annotated with "-".
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``ksymoops`` is useless on 2.6 or upper. Please use the Oops in its original
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format (from ``dmesg``, etc). Ignore any references in this or other docs to
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"decoding the Oops" or "running it through ksymoops".
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If you post an Oops from 2.6+ that has been run through ``ksymoops``,
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people will just tell you to repost it.
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Where is the Oops message is located?
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-------------------------------------
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@ -71,7 +75,7 @@ by running ``journalctl`` command.
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Sometimes ``klogd`` dies, in which case you can run ``dmesg > file`` to
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read the data from the kernel buffers and save it. Or you can
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``cat /proc/kmsg > file``, however you have to break in to stop the transfer,
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``kmsg`` is a "never ending file".
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since ``kmsg`` is a "never ending file".
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If the machine has crashed so badly that you cannot enter commands or
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the disk is not available then you have three options:
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@ -81,9 +85,9 @@ the disk is not available then you have three options:
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planned for a crash. Alternatively, you can take a picture of
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the screen with a digital camera - not nice, but better than
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nothing. If the messages scroll off the top of the console, you
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may find that booting with a higher resolution (eg, ``vga=791``)
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may find that booting with a higher resolution (e.g., ``vga=791``)
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will allow you to read more of the text. (Caveat: This needs ``vesafb``,
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so won't help for 'early' oopses)
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so won't help for 'early' oopses.)
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(2) Boot with a serial console (see
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:ref:`Documentation/admin-guide/serial-console.rst <serial_console>`),
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@ -104,7 +108,7 @@ Kernel source file. There are two methods for doing that. Usually, using
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gdb
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^^^
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The GNU debug (``gdb``) is the best way to figure out the exact file and line
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The GNU debugger (``gdb``) is the best way to figure out the exact file and line
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number of the OOPS from the ``vmlinux`` file.
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The usage of gdb works best on a kernel compiled with ``CONFIG_DEBUG_INFO``.
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@ -165,7 +169,7 @@ If you have a call trace, such as::
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[<ffffffff8802770b>] :jbd:journal_stop+0x1be/0x1ee
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...
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this shows the problem likely in the :jbd: module. You can load that module
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this shows the problem likely is in the :jbd: module. You can load that module
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in gdb and list the relevant code::
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$ gdb fs/jbd/jbd.ko
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@ -199,8 +203,9 @@ in the kernel hacking menu of the menu configuration.) For example::
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You need to be at the top level of the kernel tree for this to pick up
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your C files.
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If you don't have access to the code you can also debug on some crash dumps
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e.g. crash dump output as shown by Dave Miller::
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If you don't have access to the source code you can still debug some crash
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dumps using the following method (example crash dump output as shown by
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Dave Miller)::
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EIP is at +0x14/0x4c0
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...
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@ -230,6 +235,9 @@ e.g. crash dump output as shown by Dave Miller::
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mov 0x8(%ebp), %ebx ! %ebx = skb->sk
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mov 0x13c(%ebx), %eax ! %eax = inet_sk(sk)->opt
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file:`scripts/decodecode` can be used to automate most of this, depending
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on what CPU architecture is being debugged.
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Reporting the bug
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-----------------
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@ -241,7 +249,7 @@ used for the development of the affected code. This can be done by using
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the ``get_maintainer.pl`` script.
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For example, if you find a bug at the gspca's sonixj.c file, you can get
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their maintainers with::
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its maintainers with::
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$ ./scripts/get_maintainer.pl -f drivers/media/usb/gspca/sonixj.c
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Hans Verkuil <hverkuil@xs4all.nl> (odd fixer:GSPCA USB WEBCAM DRIVER,commit_signer:1/1=100%)
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@ -253,16 +261,17 @@ their maintainers with::
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Please notice that it will point to:
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- The last developers that touched on the source code. On the above example,
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Tejun and Bhaktipriya (in this specific case, none really envolved on the
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development of this file);
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- The last developers that touched the source code (if this is done inside
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a git tree). On the above example, Tejun and Bhaktipriya (in this
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specific case, none really envolved on the development of this file);
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- The driver maintainer (Hans Verkuil);
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- The subsystem maintainer (Mauro Carvalho Chehab);
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- The driver and/or subsystem mailing list (linux-media@vger.kernel.org);
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- the Linux Kernel mailing list (linux-kernel@vger.kernel.org).
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Usually, the fastest way to have your bug fixed is to report it to mailing
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list used for the development of the code (linux-media ML) copying the driver maintainer (Hans).
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list used for the development of the code (linux-media ML) copying the
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driver maintainer (Hans).
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If you are totally stumped as to whom to send the report, and
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``get_maintainer.pl`` didn't provide you anything useful, send it to
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@ -303,9 +312,9 @@ protection fault message can be simply cut out of the message files
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and forwarded to the kernel developers.
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Two types of address resolution are performed by ``klogd``. The first is
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static translation and the second is dynamic translation. Static
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translation uses the System.map file in much the same manner that
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ksymoops does. In order to do static translation the ``klogd`` daemon
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static translation and the second is dynamic translation.
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Static translation uses the System.map file.
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In order to do static translation the ``klogd`` daemon
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must be able to find a system map file at daemon initialization time.
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See the klogd man page for information on how ``klogd`` searches for map
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files.
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