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Sergiu Iordache4126dac2011-08-13 12:34:56 -07001Ramoops oops/panic logger
2=========================
3
4Sergiu Iordache <sergiu@chromium.org>
5
Kees Cook9ba80d92012-05-03 15:45:02 +10006Updated: 17 November 2011
Sergiu Iordache4126dac2011-08-13 12:34:56 -07007
80. Introduction
9
10Ramoops is an oops/panic logger that writes its logs to RAM before the system
11crashes. It works by logging oopses and panics in a circular buffer. Ramoops
12needs a system with persistent RAM so that the content of that area can
13survive after a restart.
14
151. Ramoops concepts
16
Tony Lindgren027bc8b02014-09-16 13:50:01 -070017Ramoops uses a predefined memory area to store the dump. The start and size
18and type of the memory area are set using three variables:
Sergiu Iordache4126dac2011-08-13 12:34:56 -070019 * "mem_address" for the start
20 * "mem_size" for the size. The memory size will be rounded down to a
21 power of two.
Tony Lindgren027bc8b02014-09-16 13:50:01 -070022 * "mem_type" to specifiy if the memory type (default is pgprot_writecombine).
23
24Typically the default value of mem_type=0 should be used as that sets the pstore
25mapping to pgprot_writecombine. Setting mem_type=1 attempts to use
26pgprot_noncached, which only works on some platforms. This is because pstore
27depends on atomic operations. At least on ARM, pgprot_noncached causes the
28memory to be mapped strongly ordered, and atomic operations on strongly ordered
29memory are implementation defined, and won't work on many ARMs such as omaps.
Sergiu Iordache4126dac2011-08-13 12:34:56 -070030
31The memory area is divided into "record_size" chunks (also rounded down to
32power of two) and each oops/panic writes a "record_size" chunk of
33information.
34
35Dumping both oopses and panics can be done by setting 1 in the "dump_oops"
36variable while setting 0 in that variable dumps only the panics.
37
38The module uses a counter to record multiple dumps but the counter gets reset
39on restart (i.e. new dumps after the restart will overwrite old ones).
40
Anton Vorontsov39eb7e972012-05-17 00:15:34 -070041Ramoops also supports software ECC protection of persistent memory regions.
42This might be useful when a hardware reset was used to bring the machine back
43to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat
44corrupt, but usually it is restorable.
45
Sergiu Iordache4126dac2011-08-13 12:34:56 -0700462. Setting the parameters
47
48Setting the ramoops parameters can be done in 2 different manners:
49 1. Use the module parameters (which have the names of the variables described
50 as before).
Anton Vorontsov958502d2012-05-26 06:20:25 -070051 For quick debugging, you can also reserve parts of memory during boot
52 and then use the reserved memory for ramoops. For example, assuming a machine
53 with > 128 MB of memory, the following kernel command line will tell the
54 kernel to use only the first 128 MB of memory, and place ECC-protected ramoops
55 region at 128 MB boundary:
56 "mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1"
Sergiu Iordache4126dac2011-08-13 12:34:56 -070057 2. Use a platform device and set the platform data. The parameters can then
58 be set through that platform data. An example of doing that is:
59
Anton Vorontsov1894a252012-05-16 05:43:08 -070060#include <linux/pstore_ram.h>
Sergiu Iordache4126dac2011-08-13 12:34:56 -070061[...]
62
63static struct ramoops_platform_data ramoops_data = {
64 .mem_size = <...>,
65 .mem_address = <...>,
Tony Lindgren027bc8b02014-09-16 13:50:01 -070066 .mem_type = <...>,
Sergiu Iordache4126dac2011-08-13 12:34:56 -070067 .record_size = <...>,
68 .dump_oops = <...>,
Anton Vorontsov39eb7e972012-05-17 00:15:34 -070069 .ecc = <...>,
Sergiu Iordache4126dac2011-08-13 12:34:56 -070070};
71
72static struct platform_device ramoops_dev = {
73 .name = "ramoops",
74 .dev = {
75 .platform_data = &ramoops_data,
76 },
77};
78
79[... inside a function ...]
80int ret;
81
82ret = platform_device_register(&ramoops_dev);
83if (ret) {
84 printk(KERN_ERR "unable to register platform device\n");
85 return ret;
86}
87
Anton Vorontsov958502d2012-05-26 06:20:25 -070088You can specify either RAM memory or peripheral devices' memory. However, when
89specifying RAM, be sure to reserve the memory by issuing memblock_reserve()
90very early in the architecture code, e.g.:
91
92#include <linux/memblock.h>
93
94memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size);
95
Sergiu Iordache4126dac2011-08-13 12:34:56 -0700963. Dump format
97
98The data dump begins with a header, currently defined as "====" followed by a
99timestamp and a new line. The dump then continues with the actual data.
100
1014. Reading the data
102
Kees Cook9ba80d92012-05-03 15:45:02 +1000103The dump data can be read from the pstore filesystem. The format for these
104files is "dmesg-ramoops-N", where N is the record number in memory. To delete
105a stored record from RAM, simply unlink the respective pstore file.
Anton Vorontsova694d1b2012-07-09 17:10:44 -0700106
1075. Persistent function tracing
108
109Persistent function tracing might be useful for debugging software or hardware
110related hangs. The functions call chain log is stored in a "ftrace-ramoops"
111file. Here is an example of usage:
112
113 # mount -t debugfs debugfs /sys/kernel/debug/
Anton Vorontsov65f8c952012-07-17 14:26:15 -0700114 # echo 1 > /sys/kernel/debug/pstore/record_ftrace
Anton Vorontsova694d1b2012-07-09 17:10:44 -0700115 # reboot -f
116 [...]
117 # mount -t pstore pstore /mnt/
118 # tail /mnt/ftrace-ramoops
119 0 ffffffff8101ea64 ffffffff8101bcda native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
120 0 ffffffff8101ea44 ffffffff8101bcf6 native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
121 0 ffffffff81020084 ffffffff8101a4b5 hpet_disable <- native_machine_shutdown+0x75/0x90
122 0 ffffffff81005f94 ffffffff8101a4bb iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
123 0 ffffffff8101a6a1 ffffffff8101a437 native_machine_emergency_restart <- native_machine_restart+0x37/0x40
124 0 ffffffff811f9876 ffffffff8101a73a acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
125 0 ffffffff8101a514 ffffffff8101a772 mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
126 0 ffffffff811d9c54 ffffffff8101a7a0 __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
127 0 ffffffff811d9c34 ffffffff811d9c80 __delay <- __const_udelay+0x30/0x40
128 0 ffffffff811d9d14 ffffffff811d9c3f delay_tsc <- __delay+0xf/0x20