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4126dacb SI |
1 | Ramoops oops/panic logger |
2 | ========================= | |
3 | ||
4 | Sergiu Iordache <sergiu@chromium.org> | |
5 | ||
9ba80d99 | 6 | Updated: 17 November 2011 |
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7 | |
8 | 0. Introduction | |
9 | ||
10 | Ramoops is an oops/panic logger that writes its logs to RAM before the system | |
11 | crashes. It works by logging oopses and panics in a circular buffer. Ramoops | |
12 | needs a system with persistent RAM so that the content of that area can | |
13 | survive after a restart. | |
14 | ||
15 | 1. Ramoops concepts | |
16 | ||
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17 | Ramoops uses a predefined memory area to store the dump. The start and size |
18 | and type of the memory area are set using three variables: | |
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19 | * "mem_address" for the start |
20 | * "mem_size" for the size. The memory size will be rounded down to a | |
21 | power of two. | |
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22 | * "mem_type" to specifiy if the memory type (default is pgprot_writecombine). |
23 | ||
24 | Typically the default value of mem_type=0 should be used as that sets the pstore | |
25 | mapping to pgprot_writecombine. Setting mem_type=1 attempts to use | |
26 | pgprot_noncached, which only works on some platforms. This is because pstore | |
27 | depends on atomic operations. At least on ARM, pgprot_noncached causes the | |
28 | memory to be mapped strongly ordered, and atomic operations on strongly ordered | |
29 | memory are implementation defined, and won't work on many ARMs such as omaps. | |
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30 | |
31 | The memory area is divided into "record_size" chunks (also rounded down to | |
32 | power of two) and each oops/panic writes a "record_size" chunk of | |
33 | information. | |
34 | ||
35 | Dumping both oopses and panics can be done by setting 1 in the "dump_oops" | |
36 | variable while setting 0 in that variable dumps only the panics. | |
37 | ||
38 | The module uses a counter to record multiple dumps but the counter gets reset | |
39 | on restart (i.e. new dumps after the restart will overwrite old ones). | |
40 | ||
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41 | Ramoops also supports software ECC protection of persistent memory regions. |
42 | This might be useful when a hardware reset was used to bring the machine back | |
43 | to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat | |
44 | corrupt, but usually it is restorable. | |
45 | ||
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46 | 2. Setting the parameters |
47 | ||
48 | Setting 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). | |
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51 | 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" | |
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57 | 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 | ||
1894a253 | 60 | #include <linux/pstore_ram.h> |
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61 | [...] |
62 | ||
63 | static struct ramoops_platform_data ramoops_data = { | |
64 | .mem_size = <...>, | |
65 | .mem_address = <...>, | |
027bc8b0 | 66 | .mem_type = <...>, |
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67 | .record_size = <...>, |
68 | .dump_oops = <...>, | |
39eb7e97 | 69 | .ecc = <...>, |
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70 | }; |
71 | ||
72 | static struct platform_device ramoops_dev = { | |
73 | .name = "ramoops", | |
74 | .dev = { | |
75 | .platform_data = &ramoops_data, | |
76 | }, | |
77 | }; | |
78 | ||
79 | [... inside a function ...] | |
80 | int ret; | |
81 | ||
82 | ret = platform_device_register(&ramoops_dev); | |
83 | if (ret) { | |
84 | printk(KERN_ERR "unable to register platform device\n"); | |
85 | return ret; | |
86 | } | |
87 | ||
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88 | You can specify either RAM memory or peripheral devices' memory. However, when |
89 | specifying RAM, be sure to reserve the memory by issuing memblock_reserve() | |
90 | very early in the architecture code, e.g.: | |
91 | ||
92 | #include <linux/memblock.h> | |
93 | ||
94 | memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); | |
95 | ||
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96 | 3. Dump format |
97 | ||
98 | The data dump begins with a header, currently defined as "====" followed by a | |
99 | timestamp and a new line. The dump then continues with the actual data. | |
100 | ||
101 | 4. Reading the data | |
102 | ||
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103 | The dump data can be read from the pstore filesystem. The format for these |
104 | files is "dmesg-ramoops-N", where N is the record number in memory. To delete | |
105 | a stored record from RAM, simply unlink the respective pstore file. | |
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106 | |
107 | 5. Persistent function tracing | |
108 | ||
109 | Persistent function tracing might be useful for debugging software or hardware | |
110 | related hangs. The functions call chain log is stored in a "ftrace-ramoops" | |
111 | file. Here is an example of usage: | |
112 | ||
113 | # mount -t debugfs debugfs /sys/kernel/debug/ | |
65f8c95e | 114 | # echo 1 > /sys/kernel/debug/pstore/record_ftrace |
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115 | # 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 |