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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
| commit | f4cdf7ca9a1fdcca413157df19753f388a5a224e (patch) | |
| tree | 60a31895b2446cd7fa27514e8c2843534a0de0da /Documentation/admin-guide/ramoops.rst | |
| download | linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.tar.gz linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.zip | |
Merge tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-mediagrafted
Pull media updates from Mauro Carvalho Chehab:
- v4l2-core: added ISP statistics support and per-block validation
- v4l2-core: Allow unknown HDR10 white point and luminance
- New camera sensors: Sony IMX678 and IMX471m, Himax HM1092 IR sensor
- New codec: Milos: VPU v2.0 codec support
- isp driver: gained support for Dreamchip RPPX1 ISP framework
- vsp1 driver: gained support for RZ/T2H and RZ/N2H
- Novalake driver: gained CVS support for new NVL hardware
- dvb-core: fix feed leak on failed DMX_ADD_PID
- several driver fixes, cleanups and minor improvements
* tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (308 commits)
media: ipu-bridge: check all DMI entries when overriding sensor rotation
media: v4l2-async: avoid deleting unlinked ASC entry on link error
media: rzg2l-cru: Align bytesperline to hardware DMA stride requirement
media: intel/ipu6: fix async notifier cleanup leak on parse error
media: staging/ipu7: fix async notifier UAF on probe error path
media: amd: isp4: fix self-deadlock in isp4sd_pwron_and_init() error path
media: amd: isp4: release partial allocations in isp4if_alloc_fw_gpumem()
media: rcar-isp: Fix VSPX reference leaks
media: rcar-isp: Release ISPCORE resources
media: i2c: imx415: Release runtime PM reference on VBLANK error
media: i2c: imx415: Return test pattern write errors
media: renesas: vsp1: Declare index variables in for loop statement
media: renesas: vsp1: Make reset control optional to support platforms without a reset line
media: dt-bindings: media: renesas,vsp1: Document RZ/T2H and RZ/N2H SoCs
media: dt-bindings: media: renesas,fcp: Document RZ/T2H and RZ/N2H SoCs
media: nxp: imx8-isi: Add additional 32-bit RGB format support
media: nxp: imx8-isi: Add 16-bit raw Bayer format support
media: nxp: imx8-isi: Implement per-stream reference counting for multiplexed streams
media: nxp: imx8-isi: Use BIT_ULL() for 64-bit stream masks
media: nxp: imx8-isi: Correct color map between V4L2 and ISI
...
Diffstat (limited to 'Documentation/admin-guide/ramoops.rst')
| -rw-r--r-- | Documentation/admin-guide/ramoops.rst | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/Documentation/admin-guide/ramoops.rst b/Documentation/admin-guide/ramoops.rst new file mode 100644 index 000000000..2eabef312 --- /dev/null +++ b/Documentation/admin-guide/ramoops.rst @@ -0,0 +1,177 @@ +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 |
