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Diffstat (limited to 'Documentation/admin-guide/bug-hunting.rst')
| -rw-r--r-- | Documentation/admin-guide/bug-hunting.rst | 53 |
1 files changed, 31 insertions, 22 deletions
diff --git a/Documentation/admin-guide/bug-hunting.rst b/Documentation/admin-guide/bug-hunting.rst index 44b8a4edd348..95299b08c405 100644 --- a/Documentation/admin-guide/bug-hunting.rst +++ b/Documentation/admin-guide/bug-hunting.rst @@ -49,15 +49,19 @@ the issue, it may also contain the word **Oops**, as on this one:: Despite being an **Oops** or some other sort of stack trace, the offended line is usually required to identify and handle the bug. Along this chapter, -we'll refer to "Oops" for all kinds of stack traces that need to be analized. +we'll refer to "Oops" for all kinds of stack traces that need to be analyzed. -.. note:: +If the kernel is compiled with ``CONFIG_DEBUG_INFO``, you can enhance the +quality of the stack trace by using file:`scripts/decode_stacktrace.sh`. + +Modules linked in +----------------- + +Modules that are tainted or are being loaded or unloaded are marked with +"(...)", where the taint flags are described in +file:`Documentation/admin-guide/tainted-kernels.rst`, "being loaded" is +annotated with "+", and "being unloaded" is annotated with "-". - ``ksymoops`` is useless on 2.6 or upper. Please use the Oops in its original - format (from ``dmesg``, etc). Ignore any references in this or other docs to - "decoding the Oops" or "running it through ksymoops". - If you post an Oops from 2.6+ that has been run through ``ksymoops``, - people will just tell you to repost it. Where is the Oops message is located? ------------------------------------- @@ -71,7 +75,7 @@ by running ``journalctl`` command. Sometimes ``klogd`` dies, in which case you can run ``dmesg > file`` to read the data from the kernel buffers and save it. Or you can ``cat /proc/kmsg > file``, however you have to break in to stop the transfer, -``kmsg`` is a "never ending file". +since ``kmsg`` is a "never ending file". If the machine has crashed so badly that you cannot enter commands or the disk is not available then you have three options: @@ -81,9 +85,9 @@ the disk is not available then you have three options: planned for a crash. Alternatively, you can take a picture of the screen with a digital camera - not nice, but better than nothing. If the messages scroll off the top of the console, you - may find that booting with a higher resolution (eg, ``vga=791``) + may find that booting with a higher resolution (e.g., ``vga=791``) will allow you to read more of the text. (Caveat: This needs ``vesafb``, - so won't help for 'early' oopses) + so won't help for 'early' oopses.) (2) Boot with a serial console (see :ref:`Documentation/admin-guide/serial-console.rst <serial_console>`), @@ -104,7 +108,7 @@ Kernel source file. There are two methods for doing that. Usually, using gdb ^^^ -The GNU debug (``gdb``) is the best way to figure out the exact file and line +The GNU debugger (``gdb``) is the best way to figure out the exact file and line number of the OOPS from the ``vmlinux`` file. The usage of gdb works best on a kernel compiled with ``CONFIG_DEBUG_INFO``. @@ -165,7 +169,7 @@ If you have a call trace, such as:: [<ffffffff8802770b>] :jbd:journal_stop+0x1be/0x1ee ... -this shows the problem likely in the :jbd: module. You can load that module +this shows the problem likely is in the :jbd: module. You can load that module in gdb and list the relevant code:: $ gdb fs/jbd/jbd.ko @@ -199,8 +203,9 @@ in the kernel hacking menu of the menu configuration.) For example:: You need to be at the top level of the kernel tree for this to pick up your C files. -If you don't have access to the code you can also debug on some crash dumps -e.g. crash dump output as shown by Dave Miller:: +If you don't have access to the source code you can still debug some crash +dumps using the following method (example crash dump output as shown by +Dave Miller):: EIP is at +0x14/0x4c0 ... @@ -230,6 +235,9 @@ e.g. crash dump output as shown by Dave Miller:: mov 0x8(%ebp), %ebx ! %ebx = skb->sk mov 0x13c(%ebx), %eax ! %eax = inet_sk(sk)->opt +file:`scripts/decodecode` can be used to automate most of this, depending +on what CPU architecture is being debugged. + Reporting the bug ----------------- @@ -241,7 +249,7 @@ used for the development of the affected code. This can be done by using the ``get_maintainer.pl`` script. For example, if you find a bug at the gspca's sonixj.c file, you can get -their maintainers with:: +its maintainers with:: $ ./scripts/get_maintainer.pl -f drivers/media/usb/gspca/sonixj.c Hans Verkuil <hverkuil@xs4all.nl> (odd fixer:GSPCA USB WEBCAM DRIVER,commit_signer:1/1=100%) @@ -253,16 +261,17 @@ their maintainers with:: Please notice that it will point to: -- The last developers that touched on the source code. On the above example, - Tejun and Bhaktipriya (in this specific case, none really envolved on the - development of this file); +- The last developers that touched the source code (if this is done inside + a git tree). On the above example, Tejun and Bhaktipriya (in this + specific case, none really involved on the development of this file); - The driver maintainer (Hans Verkuil); - The subsystem maintainer (Mauro Carvalho Chehab); - The driver and/or subsystem mailing list (linux-media@vger.kernel.org); - the Linux Kernel mailing list (linux-kernel@vger.kernel.org). Usually, the fastest way to have your bug fixed is to report it to mailing -list used for the development of the code (linux-media ML) copying the driver maintainer (Hans). +list used for the development of the code (linux-media ML) copying the +driver maintainer (Hans). If you are totally stumped as to whom to send the report, and ``get_maintainer.pl`` didn't provide you anything useful, send it to @@ -303,9 +312,9 @@ protection fault message can be simply cut out of the message files and forwarded to the kernel developers. Two types of address resolution are performed by ``klogd``. The first is -static translation and the second is dynamic translation. Static -translation uses the System.map file in much the same manner that -ksymoops does. In order to do static translation the ``klogd`` daemon +static translation and the second is dynamic translation. +Static translation uses the System.map file. +In order to do static translation the ``klogd`` daemon must be able to find a system map file at daemon initialization time. See the klogd man page for information on how ``klogd`` searches for map files. |