mirror of
https://github.com/torvalds/linux.git
synced 2024-11-24 21:21:41 +00:00
a7050ca724
For some reason my finger always hits the 'r' after typing "reserve".
Fix the typo in the Documentation example.
Fixes: d9d814eebb ("pstore/ramoops: Add ramoops.mem_name= command line option")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Link: https://lore.kernel.org/r/20240807170029.3c1ff651@gandalf.local.home
Signed-off-by: Kees Cook <kees@kernel.org>
178 lines
6.9 KiB
ReStructuredText
178 lines
6.9 KiB
ReStructuredText
Ramoops oops/panic logger
|
|
=========================
|
|
|
|
Sergiu Iordache <sergiu@chromium.org>
|
|
|
|
Updated: 10 Feb 2021
|
|
|
|
Introduction
|
|
------------
|
|
|
|
Ramoops is an oops/panic logger that writes its logs to RAM before the system
|
|
crashes. It works by logging oopses and panics in a circular buffer. Ramoops
|
|
needs a system with persistent RAM so that the content of that area can
|
|
survive after a restart.
|
|
|
|
Ramoops concepts
|
|
----------------
|
|
|
|
Ramoops uses a predefined memory area to store the dump. The start and size
|
|
and type of the memory area are set using three variables:
|
|
|
|
* ``mem_address`` for the start
|
|
* ``mem_size`` for the size. The memory size will be rounded down to a
|
|
power of two.
|
|
* ``mem_type`` to specify if the memory type (default is pgprot_writecombine).
|
|
* ``mem_name`` to specify a memory region defined by ``reserve_mem`` command
|
|
line parameter.
|
|
|
|
Typically the default value of ``mem_type=0`` should be used as that sets the pstore
|
|
mapping to pgprot_writecombine. Setting ``mem_type=1`` attempts to use
|
|
``pgprot_noncached``, which only works on some platforms. This is because pstore
|
|
depends on atomic operations. At least on ARM, pgprot_noncached causes the
|
|
memory to be mapped strongly ordered, and atomic operations on strongly ordered
|
|
memory are implementation defined, and won't work on many ARMs such as omaps.
|
|
Setting ``mem_type=2`` attempts to treat the memory region as normal memory,
|
|
which enables full cache on it. This can improve the performance.
|
|
|
|
The memory area is divided into ``record_size`` chunks (also rounded down to
|
|
power of two) and each kmesg dump writes a ``record_size`` chunk of
|
|
information.
|
|
|
|
Limiting which kinds of kmsg dumps are stored can be controlled via
|
|
the ``max_reason`` value, as defined in include/linux/kmsg_dump.h's
|
|
``enum kmsg_dump_reason``. For example, to store both Oopses and Panics,
|
|
``max_reason`` should be set to 2 (KMSG_DUMP_OOPS), to store only Panics
|
|
``max_reason`` should be set to 1 (KMSG_DUMP_PANIC). Setting this to 0
|
|
(KMSG_DUMP_UNDEF), means the reason filtering will be controlled by the
|
|
``printk.always_kmsg_dump`` boot param: if unset, it'll be KMSG_DUMP_OOPS,
|
|
otherwise KMSG_DUMP_MAX.
|
|
|
|
The module uses a counter to record multiple dumps but the counter gets reset
|
|
on restart (i.e. new dumps after the restart will overwrite old ones).
|
|
|
|
Ramoops also supports software ECC protection of persistent memory regions.
|
|
This might be useful when a hardware reset was used to bring the machine back
|
|
to life (i.e. a watchdog triggered). In such cases, RAM may be somewhat
|
|
corrupt, but usually it is restorable.
|
|
|
|
Setting the parameters
|
|
----------------------
|
|
|
|
Setting the ramoops parameters can be done in several different manners:
|
|
|
|
A. Use the module parameters (which have the names of the variables described
|
|
as before). For quick debugging, you can also reserve parts of memory during
|
|
boot and then use the reserved memory for ramoops. For example, assuming a
|
|
machine with > 128 MB of memory, the following kernel command line will tell
|
|
the kernel to use only the first 128 MB of memory, and place ECC-protected
|
|
ramoops region at 128 MB boundary::
|
|
|
|
mem=128M ramoops.mem_address=0x8000000 ramoops.ecc=1
|
|
|
|
B. Use Device Tree bindings, as described in
|
|
``Documentation/devicetree/bindings/reserved-memory/ramoops.yaml``.
|
|
For example::
|
|
|
|
reserved-memory {
|
|
#address-cells = <2>;
|
|
#size-cells = <2>;
|
|
ranges;
|
|
|
|
ramoops@8f000000 {
|
|
compatible = "ramoops";
|
|
reg = <0 0x8f000000 0 0x100000>;
|
|
record-size = <0x4000>;
|
|
console-size = <0x4000>;
|
|
};
|
|
};
|
|
|
|
C. Use a platform device and set the platform data. The parameters can then
|
|
be set through that platform data. An example of doing that is:
|
|
|
|
.. code-block:: c
|
|
|
|
#include <linux/pstore_ram.h>
|
|
[...]
|
|
|
|
static struct ramoops_platform_data ramoops_data = {
|
|
.mem_size = <...>,
|
|
.mem_address = <...>,
|
|
.mem_type = <...>,
|
|
.record_size = <...>,
|
|
.max_reason = <...>,
|
|
.ecc = <...>,
|
|
};
|
|
|
|
static struct platform_device ramoops_dev = {
|
|
.name = "ramoops",
|
|
.dev = {
|
|
.platform_data = &ramoops_data,
|
|
},
|
|
};
|
|
|
|
[... inside a function ...]
|
|
int ret;
|
|
|
|
ret = platform_device_register(&ramoops_dev);
|
|
if (ret) {
|
|
printk(KERN_ERR "unable to register platform device\n");
|
|
return ret;
|
|
}
|
|
|
|
D. Using a region of memory reserved via ``reserve_mem`` command line
|
|
parameter. The address and size will be defined by the ``reserve_mem``
|
|
parameter. Note, that ``reserve_mem`` may not always allocate memory
|
|
in the same location, and cannot be relied upon. Testing will need
|
|
to be done, and it may not work on every machine, nor every kernel.
|
|
Consider this a "best effort" approach. The ``reserve_mem`` option
|
|
takes a size, alignment and name as arguments. The name is used
|
|
to map the memory to a label that can be retrieved by ramoops.
|
|
|
|
reserve_mem=2M:4096:oops ramoops.mem_name=oops
|
|
|
|
You can specify either RAM memory or peripheral devices' memory. However, when
|
|
specifying RAM, be sure to reserve the memory by issuing memblock_reserve()
|
|
very early in the architecture code, e.g.::
|
|
|
|
#include <linux/memblock.h>
|
|
|
|
memblock_reserve(ramoops_data.mem_address, ramoops_data.mem_size);
|
|
|
|
Dump format
|
|
-----------
|
|
|
|
The data dump begins with a header, currently defined as ``====`` followed by a
|
|
timestamp and a new line. The dump then continues with the actual data.
|
|
|
|
Reading the data
|
|
----------------
|
|
|
|
The dump data can be read from the pstore filesystem. The format for these
|
|
files is ``dmesg-ramoops-N``, where N is the record number in memory. To delete
|
|
a stored record from RAM, simply unlink the respective pstore file.
|
|
|
|
Persistent function tracing
|
|
---------------------------
|
|
|
|
Persistent function tracing might be useful for debugging software or hardware
|
|
related hangs. The functions call chain log is stored in a ``ftrace-ramoops``
|
|
file. Here is an example of usage::
|
|
|
|
# mount -t debugfs debugfs /sys/kernel/debug/
|
|
# echo 1 > /sys/kernel/debug/pstore/record_ftrace
|
|
# reboot -f
|
|
[...]
|
|
# mount -t pstore pstore /mnt/
|
|
# tail /mnt/ftrace-ramoops
|
|
0 ffffffff8101ea64 ffffffff8101bcda native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
|
|
0 ffffffff8101ea44 ffffffff8101bcf6 native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
|
|
0 ffffffff81020084 ffffffff8101a4b5 hpet_disable <- native_machine_shutdown+0x75/0x90
|
|
0 ffffffff81005f94 ffffffff8101a4bb iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
|
|
0 ffffffff8101a6a1 ffffffff8101a437 native_machine_emergency_restart <- native_machine_restart+0x37/0x40
|
|
0 ffffffff811f9876 ffffffff8101a73a acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
|
|
0 ffffffff8101a514 ffffffff8101a772 mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
|
|
0 ffffffff811d9c54 ffffffff8101a7a0 __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
|
|
0 ffffffff811d9c34 ffffffff811d9c80 __delay <- __const_udelay+0x30/0x40
|
|
0 ffffffff811d9d14 ffffffff811d9c3f delay_tsc <- __delay+0xf/0x20
|