view Documentation/oops-tracing.txt @ 452:c7ed6fe5dca0

kexec: dont initialise regions in reserve_memory()

There is no need to initialise efi_memmap_res and boot_param_res in
reserve_memory() for the initial xen domain as it is done in
machine_kexec_setup_resources() using values from the kexec hypercall.

Signed-off-by: Simon Horman <horms@verge.net.au>
author Keir Fraser <keir.fraser@citrix.com>
date Thu Feb 28 10:55:18 2008 +0000 (2008-02-28)
parents 831230e53067
line source
1 NOTE: ksymoops is useless on 2.6. Please use the Oops in its original format
2 (from dmesg, etc). Ignore any references in this or other docs to "decoding
3 the Oops" or "running it through ksymoops". If you post an Oops from 2.6 that
4 has been run through ksymoops, people will just tell you to repost it.
6 Quick Summary
7 -------------
9 Find the Oops and send it to the maintainer of the kernel area that seems to be
10 involved with the problem. Don't worry too much about getting the wrong person.
11 If you are unsure send it to the person responsible for the code relevant to
12 what you were doing. If it occurs repeatably try and describe how to recreate
13 it. That's worth even more than the oops.
15 If you are totally stumped as to whom to send the report, send it to
16 linux-kernel@vger.kernel.org. Thanks for your help in making Linux as
17 stable as humanly possible.
19 Where is the Oops?
20 ----------------------
22 Normally the Oops text is read from the kernel buffers by klogd and
23 handed to syslogd which writes it to a syslog file, typically
24 /var/log/messages (depends on /etc/syslog.conf). Sometimes klogd dies,
25 in which case you can run dmesg > file to read the data from the kernel
26 buffers and save it. Or you can cat /proc/kmsg > file, however you
27 have to break in to stop the transfer, kmsg is a "never ending file".
28 If the machine has crashed so badly that you cannot enter commands or
29 the disk is not available then you have three options :-
31 (1) Hand copy the text from the screen and type it in after the machine
32 has restarted. Messy but it is the only option if you have not
33 planned for a crash. Alternatively, you can take a picture of
34 the screen with a digital camera - not nice, but better than
35 nothing. If the messages scroll off the top of the console, you
36 may find that booting with a higher resolution (eg, vga=791)
37 will allow you to read more of the text. (Caveat: This needs vesafb,
38 so won't help for 'early' oopses)
40 (2) Boot with a serial console (see Documentation/serial-console.txt),
41 run a null modem to a second machine and capture the output there
42 using your favourite communication program. Minicom works well.
44 (3) Use Kdump (see Documentation/kdump/kdump.txt),
45 extract the kernel ring buffer from old memory with using dmesg
46 gdbmacro in Documentation/kdump/gdbmacros.txt.
49 Full Information
50 ----------------
52 NOTE: the message from Linus below applies to 2.4 kernel. I have preserved it
53 for historical reasons, and because some of the information in it still
54 applies. Especially, please ignore any references to ksymoops.
56 From: Linus Torvalds <torvalds@osdl.org>
58 How to track down an Oops.. [originally a mail to linux-kernel]
60 The main trick is having 5 years of experience with those pesky oops
61 messages ;-)
63 Actually, there are things you can do that make this easier. I have two
64 separate approaches:
66 gdb /usr/src/linux/vmlinux
67 gdb> disassemble <offending_function>
69 That's the easy way to find the problem, at least if the bug-report is
70 well made (like this one was - run through ksymoops to get the
71 information of which function and the offset in the function that it
72 happened in).
74 Oh, it helps if the report happens on a kernel that is compiled with the
75 same compiler and similar setups.
77 The other thing to do is disassemble the "Code:" part of the bug report:
78 ksymoops will do this too with the correct tools, but if you don't have
79 the tools you can just do a silly program:
81 char str[] = "\xXX\xXX\xXX...";
82 main(){}
84 and compile it with gcc -g and then do "disassemble str" (where the "XX"
85 stuff are the values reported by the Oops - you can just cut-and-paste
86 and do a replace of spaces to "\x" - that's what I do, as I'm too lazy
87 to write a program to automate this all).
89 Finally, if you want to see where the code comes from, you can do
91 cd /usr/src/linux
92 make fs/buffer.s # or whatever file the bug happened in
94 and then you get a better idea of what happens than with the gdb
95 disassembly.
97 Now, the trick is just then to combine all the data you have: the C
98 sources (and general knowledge of what it _should_ do), the assembly
99 listing and the code disassembly (and additionally the register dump you
100 also get from the "oops" message - that can be useful to see _what_ the
101 corrupted pointers were, and when you have the assembler listing you can
102 also match the other registers to whatever C expressions they were used
103 for).
105 Essentially, you just look at what doesn't match (in this case it was the
106 "Code" disassembly that didn't match with what the compiler generated).
107 Then you need to find out _why_ they don't match. Often it's simple - you
108 see that the code uses a NULL pointer and then you look at the code and
109 wonder how the NULL pointer got there, and if it's a valid thing to do
110 you just check against it..
112 Now, if somebody gets the idea that this is time-consuming and requires
113 some small amount of concentration, you're right. Which is why I will
114 mostly just ignore any panic reports that don't have the symbol table
115 info etc looked up: it simply gets too hard to look it up (I have some
116 programs to search for specific patterns in the kernel code segment, and
117 sometimes I have been able to look up those kinds of panics too, but
118 that really requires pretty good knowledge of the kernel just to be able
119 to pick out the right sequences etc..)
121 _Sometimes_ it happens that I just see the disassembled code sequence
122 from the panic, and I know immediately where it's coming from. That's when
123 I get worried that I've been doing this for too long ;-)
125 Linus
128 ---------------------------------------------------------------------------
129 Notes on Oops tracing with klogd:
131 In order to help Linus and the other kernel developers there has been
132 substantial support incorporated into klogd for processing protection
133 faults. In order to have full support for address resolution at least
134 version 1.3-pl3 of the sysklogd package should be used.
136 When a protection fault occurs the klogd daemon automatically
137 translates important addresses in the kernel log messages to their
138 symbolic equivalents. This translated kernel message is then
139 forwarded through whatever reporting mechanism klogd is using. The
140 protection fault message can be simply cut out of the message files
141 and forwarded to the kernel developers.
143 Two types of address resolution are performed by klogd. The first is
144 static translation and the second is dynamic translation. Static
145 translation uses the System.map file in much the same manner that
146 ksymoops does. In order to do static translation the klogd daemon
147 must be able to find a system map file at daemon initialization time.
148 See the klogd man page for information on how klogd searches for map
149 files.
151 Dynamic address translation is important when kernel loadable modules
152 are being used. Since memory for kernel modules is allocated from the
153 kernel's dynamic memory pools there are no fixed locations for either
154 the start of the module or for functions and symbols in the module.
156 The kernel supports system calls which allow a program to determine
157 which modules are loaded and their location in memory. Using these
158 system calls the klogd daemon builds a symbol table which can be used
159 to debug a protection fault which occurs in a loadable kernel module.
161 At the very minimum klogd will provide the name of the module which
162 generated the protection fault. There may be additional symbolic
163 information available if the developer of the loadable module chose to
164 export symbol information from the module.
166 Since the kernel module environment can be dynamic there must be a
167 mechanism for notifying the klogd daemon when a change in module
168 environment occurs. There are command line options available which
169 allow klogd to signal the currently executing daemon that symbol
170 information should be refreshed. See the klogd manual page for more
171 information.
173 A patch is included with the sysklogd distribution which modifies the
174 modules-2.0.0 package to automatically signal klogd whenever a module
175 is loaded or unloaded. Applying this patch provides essentially
176 seamless support for debugging protection faults which occur with
177 kernel loadable modules.
179 The following is an example of a protection fault in a loadable module
180 processed by klogd:
181 ---------------------------------------------------------------------------
182 Aug 29 09:51:01 blizard kernel: Unable to handle kernel paging request at virtual address f15e97cc
183 Aug 29 09:51:01 blizard kernel: current->tss.cr3 = 0062d000, %cr3 = 0062d000
184 Aug 29 09:51:01 blizard kernel: *pde = 00000000
185 Aug 29 09:51:01 blizard kernel: Oops: 0002
186 Aug 29 09:51:01 blizard kernel: CPU: 0
187 Aug 29 09:51:01 blizard kernel: EIP: 0010:[oops:_oops+16/3868]
188 Aug 29 09:51:01 blizard kernel: EFLAGS: 00010212
189 Aug 29 09:51:01 blizard kernel: eax: 315e97cc ebx: 003a6f80 ecx: 001be77b edx: 00237c0c
190 Aug 29 09:51:01 blizard kernel: esi: 00000000 edi: bffffdb3 ebp: 00589f90 esp: 00589f8c
191 Aug 29 09:51:01 blizard kernel: ds: 0018 es: 0018 fs: 002b gs: 002b ss: 0018
192 Aug 29 09:51:01 blizard kernel: Process oops_test (pid: 3374, process nr: 21, stackpage=00589000)
193 Aug 29 09:51:01 blizard kernel: Stack: 315e97cc 00589f98 0100b0b4 bffffed4 0012e38e 00240c64 003a6f80 00000001
194 Aug 29 09:51:01 blizard kernel: 00000000 00237810 bfffff00 0010a7fa 00000003 00000001 00000000 bfffff00
195 Aug 29 09:51:01 blizard kernel: bffffdb3 bffffed4 ffffffda 0000002b 0007002b 0000002b 0000002b 00000036
196 Aug 29 09:51:01 blizard kernel: Call Trace: [oops:_oops_ioctl+48/80] [_sys_ioctl+254/272] [_system_call+82/128]
197 Aug 29 09:51:01 blizard kernel: Code: c7 00 05 00 00 00 eb 08 90 90 90 90 90 90 90 90 89 ec 5d c3
198 ---------------------------------------------------------------------------
200 Dr. G.W. Wettstein Oncology Research Div. Computing Facility
201 Roger Maris Cancer Center INTERNET: greg@wind.rmcc.com
202 820 4th St. N.
203 Fargo, ND 58122
204 Phone: 701-234-7556
207 ---------------------------------------------------------------------------
208 Tainted kernels:
210 Some oops reports contain the string 'Tainted: ' after the program
211 counter. This indicates that the kernel has been tainted by some
212 mechanism. The string is followed by a series of position-sensitive
213 characters, each representing a particular tainted value.
215 1: 'G' if all modules loaded have a GPL or compatible license, 'P' if
216 any proprietary module has been loaded. Modules without a
217 MODULE_LICENSE or with a MODULE_LICENSE that is not recognised by
218 insmod as GPL compatible are assumed to be proprietary.
220 2: 'F' if any module was force loaded by "insmod -f", ' ' if all
221 modules were loaded normally.
223 3: 'S' if the oops occurred on an SMP kernel running on hardware that
224 hasn't been certified as safe to run multiprocessor.
225 Currently this occurs only on various Athlons that are not
226 SMP capable.
228 4: 'R' if a module was force unloaded by "rmmod -f", ' ' if all
229 modules were unloaded normally.
231 5: 'M' if any processor has reported a Machine Check Exception,
232 ' ' if no Machine Check Exceptions have occurred.
234 6: 'B' if a page-release function has found a bad page reference or
235 some unexpected page flags.
237 The primary reason for the 'Tainted: ' string is to tell kernel
238 debuggers if this is a clean kernel or if anything unusual has
239 occurred. Tainting is permanent: even if an offending module is
240 unloaded, the tainted value remains to indicate that the kernel is not
241 trustworthy.