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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 |
4126dacb SI |
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 | ||
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48 | Setting the ramoops parameters can be done in several different manners: |
49 | ||
50 | A. Use the module parameters (which have the names of the variables described | |
51 | as before). For quick debugging, you can also reserve parts of memory during | |
52 | boot and then use the reserved memory for ramoops. For example, assuming a | |
53 | machine with > 128 MB of memory, the following kernel command line will tell | |
54 | the kernel to use only the first 128 MB of memory, and place ECC-protected | |
55 | ramoops region at 128 MB boundary: | |
958502d8 | 56 | "mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1" |
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57 | |
58 | B. Use Device Tree bindings, as described in | |
59 | Documentation/device-tree/bindings/reserved-memory/ramoops.txt. | |
60 | For example: | |
61 | ||
62 | reserved-memory { | |
63 | #address-cells = <2>; | |
64 | #size-cells = <2>; | |
65 | ranges; | |
66 | ||
67 | ramoops@8f000000 { | |
68 | compatible = "ramoops"; | |
69 | reg = <0 0x8f000000 0 0x100000>; | |
70 | record-size = <0x4000>; | |
71 | console-size = <0x4000>; | |
72 | }; | |
73 | }; | |
74 | ||
75 | C. Use a platform device and set the platform data. The parameters can then | |
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76 | be set through that platform data. An example of doing that is: |
77 | ||
1894a253 | 78 | #include <linux/pstore_ram.h> |
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79 | [...] |
80 | ||
81 | static struct ramoops_platform_data ramoops_data = { | |
82 | .mem_size = <...>, | |
83 | .mem_address = <...>, | |
027bc8b0 | 84 | .mem_type = <...>, |
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85 | .record_size = <...>, |
86 | .dump_oops = <...>, | |
39eb7e97 | 87 | .ecc = <...>, |
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88 | }; |
89 | ||
90 | static struct platform_device ramoops_dev = { | |
91 | .name = "ramoops", | |
92 | .dev = { | |
93 | .platform_data = &ramoops_data, | |
94 | }, | |
95 | }; | |
96 | ||
97 | [... inside a function ...] | |
98 | int ret; | |
99 | ||
100 | ret = platform_device_register(&ramoops_dev); | |
101 | if (ret) { | |
102 | printk(KERN_ERR "unable to register platform device\n"); | |
103 | return ret; | |
104 | } | |
105 | ||
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106 | You can specify either RAM memory or peripheral devices' memory. However, when |
107 | specifying RAM, be sure to reserve the memory by issuing memblock_reserve() | |
108 | very early in the architecture code, e.g.: | |
109 | ||
110 | #include <linux/memblock.h> | |
111 | ||
112 | memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); | |
113 | ||
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114 | 3. Dump format |
115 | ||
116 | The data dump begins with a header, currently defined as "====" followed by a | |
117 | timestamp and a new line. The dump then continues with the actual data. | |
118 | ||
119 | 4. Reading the data | |
120 | ||
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121 | The dump data can be read from the pstore filesystem. The format for these |
122 | files is "dmesg-ramoops-N", where N is the record number in memory. To delete | |
123 | a stored record from RAM, simply unlink the respective pstore file. | |
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124 | |
125 | 5. Persistent function tracing | |
126 | ||
127 | Persistent function tracing might be useful for debugging software or hardware | |
128 | related hangs. The functions call chain log is stored in a "ftrace-ramoops" | |
129 | file. Here is an example of usage: | |
130 | ||
131 | # mount -t debugfs debugfs /sys/kernel/debug/ | |
65f8c95e | 132 | # echo 1 > /sys/kernel/debug/pstore/record_ftrace |
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133 | # reboot -f |
134 | [...] | |
135 | # mount -t pstore pstore /mnt/ | |
136 | # tail /mnt/ftrace-ramoops | |
137 | 0 ffffffff8101ea64 ffffffff8101bcda native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0 | |
138 | 0 ffffffff8101ea44 ffffffff8101bcf6 native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0 | |
139 | 0 ffffffff81020084 ffffffff8101a4b5 hpet_disable <- native_machine_shutdown+0x75/0x90 | |
140 | 0 ffffffff81005f94 ffffffff8101a4bb iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90 | |
141 | 0 ffffffff8101a6a1 ffffffff8101a437 native_machine_emergency_restart <- native_machine_restart+0x37/0x40 | |
142 | 0 ffffffff811f9876 ffffffff8101a73a acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0 | |
143 | 0 ffffffff8101a514 ffffffff8101a772 mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0 | |
144 | 0 ffffffff811d9c54 ffffffff8101a7a0 __const_udelay <- native_machine_emergency_restart+0x110/0x1e0 | |
145 | 0 ffffffff811d9c34 ffffffff811d9c80 __delay <- __const_udelay+0x30/0x40 | |
146 | 0 ffffffff811d9d14 ffffffff811d9c3f delay_tsc <- __delay+0xf/0x20 |