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1 | Ramoops oops/panic logger |
2 | ========================= | |
3 | ||
4 | Sergiu Iordache <sergiu@chromium.org> | |
5 | ||
9d843e8f | 6 | Updated: 10 Feb 2021 |
4126dacb | 7 | |
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8 | Introduction |
9 | ------------ | |
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10 | |
11 | Ramoops is an oops/panic logger that writes its logs to RAM before the system | |
12 | crashes. It works by logging oopses and panics in a circular buffer. Ramoops | |
13 | needs a system with persistent RAM so that the content of that area can | |
14 | survive after a restart. | |
15 | ||
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16 | Ramoops concepts |
17 | ---------------- | |
4126dacb | 18 | |
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19 | Ramoops uses a predefined memory area to store the dump. The start and size |
20 | and type of the memory area are set using three variables: | |
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21 | |
22 | * ``mem_address`` for the start | |
23 | * ``mem_size`` for the size. The memory size will be rounded down to a | |
24 | power of two. | |
751d5b27 | 25 | * ``mem_type`` to specify if the memory type (default is pgprot_writecombine). |
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26 | |
27 | Typically the default value of ``mem_type=0`` should be used as that sets the pstore | |
28 | mapping to pgprot_writecombine. Setting ``mem_type=1`` attempts to use | |
29 | ``pgprot_noncached``, which only works on some platforms. This is because pstore | |
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30 | depends on atomic operations. At least on ARM, pgprot_noncached causes the |
31 | memory to be mapped strongly ordered, and atomic operations on strongly ordered | |
32 | memory are implementation defined, and won't work on many ARMs such as omaps. | |
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33 | Setting ``mem_type=2`` attempts to treat the memory region as normal memory, |
34 | which enables full cache on it. This can improve the performance. | |
4126dacb | 35 | |
b2777b65 | 36 | The memory area is divided into ``record_size`` chunks (also rounded down to |
791205e3 | 37 | power of two) and each kmesg dump writes a ``record_size`` chunk of |
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38 | information. |
39 | ||
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40 | Limiting which kinds of kmsg dumps are stored can be controlled via |
41 | the ``max_reason`` value, as defined in include/linux/kmsg_dump.h's | |
42 | ``enum kmsg_dump_reason``. For example, to store both Oopses and Panics, | |
43 | ``max_reason`` should be set to 2 (KMSG_DUMP_OOPS), to store only Panics | |
44 | ``max_reason`` should be set to 1 (KMSG_DUMP_PANIC). Setting this to 0 | |
45 | (KMSG_DUMP_UNDEF), means the reason filtering will be controlled by the | |
46 | ``printk.always_kmsg_dump`` boot param: if unset, it'll be KMSG_DUMP_OOPS, | |
47 | otherwise KMSG_DUMP_MAX. | |
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48 | |
49 | The module uses a counter to record multiple dumps but the counter gets reset | |
50 | on restart (i.e. new dumps after the restart will overwrite old ones). | |
51 | ||
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52 | Ramoops also supports software ECC protection of persistent memory regions. |
53 | This might be useful when a hardware reset was used to bring the machine back | |
54 | to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat | |
55 | corrupt, but usually it is restorable. | |
56 | ||
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57 | Setting the parameters |
58 | ---------------------- | |
4126dacb | 59 | |
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60 | Setting the ramoops parameters can be done in several different manners: |
61 | ||
62 | A. Use the module parameters (which have the names of the variables described | |
63 | as before). For quick debugging, you can also reserve parts of memory during | |
64 | boot and then use the reserved memory for ramoops. For example, assuming a | |
65 | machine with > 128 MB of memory, the following kernel command line will tell | |
66 | the kernel to use only the first 128 MB of memory, and place ECC-protected | |
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67 | ramoops region at 128 MB boundary:: |
68 | ||
69 | mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1 | |
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70 | |
71 | B. Use Device Tree bindings, as described in | |
fad956fc | 72 | ``Documentation/devicetree/bindings/reserved-memory/ramoops.yaml``. |
b2777b65 | 73 | For example:: |
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74 | |
75 | reserved-memory { | |
76 | #address-cells = <2>; | |
77 | #size-cells = <2>; | |
78 | ranges; | |
79 | ||
80 | ramoops@8f000000 { | |
81 | compatible = "ramoops"; | |
82 | reg = <0 0x8f000000 0 0x100000>; | |
83 | record-size = <0x4000>; | |
84 | console-size = <0x4000>; | |
85 | }; | |
86 | }; | |
87 | ||
88 | C. Use a platform device and set the platform data. The parameters can then | |
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89 | be set through that platform data. An example of doing that is: |
90 | ||
91 | .. code-block:: c | |
4126dacb | 92 | |
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93 | #include <linux/pstore_ram.h> |
94 | [...] | |
4126dacb | 95 | |
b2777b65 | 96 | static struct ramoops_platform_data ramoops_data = { |
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97 | .mem_size = <...>, |
98 | .mem_address = <...>, | |
027bc8b0 | 99 | .mem_type = <...>, |
4126dacb | 100 | .record_size = <...>, |
791205e3 | 101 | .max_reason = <...>, |
39eb7e97 | 102 | .ecc = <...>, |
b2777b65 | 103 | }; |
4126dacb | 104 | |
b2777b65 | 105 | static struct platform_device ramoops_dev = { |
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106 | .name = "ramoops", |
107 | .dev = { | |
108 | .platform_data = &ramoops_data, | |
109 | }, | |
b2777b65 | 110 | }; |
4126dacb | 111 | |
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112 | [... inside a function ...] |
113 | int ret; | |
4126dacb | 114 | |
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115 | ret = platform_device_register(&ramoops_dev); |
116 | if (ret) { | |
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117 | printk(KERN_ERR "unable to register platform device\n"); |
118 | return ret; | |
b2777b65 | 119 | } |
4126dacb | 120 | |
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121 | You can specify either RAM memory or peripheral devices' memory. However, when |
122 | specifying RAM, be sure to reserve the memory by issuing memblock_reserve() | |
b2777b65 | 123 | very early in the architecture code, e.g.:: |
958502d8 | 124 | |
b2777b65 | 125 | #include <linux/memblock.h> |
958502d8 | 126 | |
b2777b65 | 127 | memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size); |
958502d8 | 128 | |
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129 | Dump format |
130 | ----------- | |
4126dacb | 131 | |
b2777b65 | 132 | The data dump begins with a header, currently defined as ``====`` followed by a |
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133 | timestamp and a new line. The dump then continues with the actual data. |
134 | ||
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135 | Reading the data |
136 | ---------------- | |
4126dacb | 137 | |
9ba80d99 | 138 | The dump data can be read from the pstore filesystem. The format for these |
b2777b65 | 139 | files is ``dmesg-ramoops-N``, where N is the record number in memory. To delete |
9ba80d99 | 140 | a stored record from RAM, simply unlink the respective pstore file. |
a694d1b5 | 141 | |
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142 | Persistent function tracing |
143 | --------------------------- | |
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144 | |
145 | Persistent function tracing might be useful for debugging software or hardware | |
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146 | related hangs. The functions call chain log is stored in a ``ftrace-ramoops`` |
147 | file. Here is an example of usage:: | |
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148 | |
149 | # mount -t debugfs debugfs /sys/kernel/debug/ | |
65f8c95e | 150 | # echo 1 > /sys/kernel/debug/pstore/record_ftrace |
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151 | # reboot -f |
152 | [...] | |
153 | # mount -t pstore pstore /mnt/ | |
154 | # tail /mnt/ftrace-ramoops | |
155 | 0 ffffffff8101ea64 ffffffff8101bcda native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0 | |
156 | 0 ffffffff8101ea44 ffffffff8101bcf6 native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0 | |
157 | 0 ffffffff81020084 ffffffff8101a4b5 hpet_disable <- native_machine_shutdown+0x75/0x90 | |
158 | 0 ffffffff81005f94 ffffffff8101a4bb iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90 | |
159 | 0 ffffffff8101a6a1 ffffffff8101a437 native_machine_emergency_restart <- native_machine_restart+0x37/0x40 | |
160 | 0 ffffffff811f9876 ffffffff8101a73a acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0 | |
161 | 0 ffffffff8101a514 ffffffff8101a772 mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0 | |
162 | 0 ffffffff811d9c54 ffffffff8101a7a0 __const_udelay <- native_machine_emergency_restart+0x110/0x1e0 | |
163 | 0 ffffffff811d9c34 ffffffff811d9c80 __delay <- __const_udelay+0x30/0x40 | |
164 | 0 ffffffff811d9d14 ffffffff811d9c3f delay_tsc <- __delay+0xf/0x20 |