mirror of
https://github.com/edk2-porting/linux-next.git
synced 2024-12-25 21:54:06 +08:00
c811659bb9
Remove redundant details of blkdev and fix up resulting kerndoc. Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Kees Cook <keescook@chromium.org>
235 lines
8.8 KiB
ReStructuredText
235 lines
8.8 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
pstore block oops/panic logger
|
|
==============================
|
|
|
|
Introduction
|
|
------------
|
|
|
|
pstore block (pstore/blk) is an oops/panic logger that writes its logs to a
|
|
block device and non-block device before the system crashes. You can get
|
|
these log files by mounting pstore filesystem like::
|
|
|
|
mount -t pstore pstore /sys/fs/pstore
|
|
|
|
|
|
pstore block concepts
|
|
---------------------
|
|
|
|
pstore/blk provides efficient configuration method for pstore/blk, which
|
|
divides all configurations into two parts, configurations for user and
|
|
configurations for driver.
|
|
|
|
Configurations for user determine how pstore/blk works, such as pmsg_size,
|
|
kmsg_size and so on. All of them support both Kconfig and module parameters,
|
|
but module parameters have priority over Kconfig.
|
|
|
|
Configurations for driver are all about block device and non-block device,
|
|
such as total_size of block device and read/write operations.
|
|
|
|
Configurations for user
|
|
-----------------------
|
|
|
|
All of these configurations support both Kconfig and module parameters, but
|
|
module parameters have priority over Kconfig.
|
|
|
|
Here is an example for module parameters::
|
|
|
|
pstore_blk.blkdev=/dev/mmcblk0p7 pstore_blk.kmsg_size=64 best_effort=y
|
|
|
|
The detail of each configurations may be of interest to you.
|
|
|
|
blkdev
|
|
~~~~~~
|
|
|
|
The block device to use. Most of the time, it is a partition of block device.
|
|
It's required for pstore/blk. It is also used for MTD device.
|
|
|
|
When pstore/blk is built as a module, "blkdev" accepts the following variants:
|
|
|
|
1. /dev/<disk_name> represents the device number of disk
|
|
#. /dev/<disk_name><decimal> represents the device number of partition - device
|
|
number of disk plus the partition number
|
|
#. /dev/<disk_name>p<decimal> - same as the above; this form is used when disk
|
|
name of partitioned disk ends with a digit.
|
|
|
|
When pstore/blk is built into the kernel, "blkdev" accepts the following variants:
|
|
|
|
#. <hex_major><hex_minor> device number in hexadecimal representation,
|
|
with no leading 0x, for example b302.
|
|
#. PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF represents the unique id of
|
|
a partition if the partition table provides it. The UUID may be either an
|
|
EFI/GPT UUID, or refer to an MSDOS partition using the format SSSSSSSS-PP,
|
|
where SSSSSSSS is a zero-filled hex representation of the 32-bit
|
|
"NT disk signature", and PP is a zero-filled hex representation of the
|
|
1-based partition number.
|
|
#. PARTUUID=<UUID>/PARTNROFF=<int> to select a partition in relation to a
|
|
partition with a known unique id.
|
|
#. <major>:<minor> major and minor number of the device separated by a colon.
|
|
|
|
It accepts the following variants for MTD device:
|
|
|
|
1. <device name> MTD device name. "pstore" is recommended.
|
|
#. <device number> MTD device number.
|
|
|
|
kmsg_size
|
|
~~~~~~~~~
|
|
|
|
The chunk size in KB for oops/panic front-end. It **MUST** be a multiple of 4.
|
|
It's optional if you do not care oops/panic log.
|
|
|
|
There are multiple chunks for oops/panic front-end depending on the remaining
|
|
space except other pstore front-ends.
|
|
|
|
pstore/blk will log to oops/panic chunks one by one, and always overwrite the
|
|
oldest chunk if there is no more free chunk.
|
|
|
|
pmsg_size
|
|
~~~~~~~~~
|
|
|
|
The chunk size in KB for pmsg front-end. It **MUST** be a multiple of 4.
|
|
It's optional if you do not care pmsg log.
|
|
|
|
Unlike oops/panic front-end, there is only one chunk for pmsg front-end.
|
|
|
|
Pmsg is a user space accessible pstore object. Writes to */dev/pmsg0* are
|
|
appended to the chunk. On reboot the contents are available in
|
|
*/sys/fs/pstore/pmsg-pstore-blk-0*.
|
|
|
|
console_size
|
|
~~~~~~~~~~~~
|
|
|
|
The chunk size in KB for console front-end. It **MUST** be a multiple of 4.
|
|
It's optional if you do not care console log.
|
|
|
|
Similar to pmsg front-end, there is only one chunk for console front-end.
|
|
|
|
All log of console will be appended to the chunk. On reboot the contents are
|
|
available in */sys/fs/pstore/console-pstore-blk-0*.
|
|
|
|
ftrace_size
|
|
~~~~~~~~~~~
|
|
|
|
The chunk size in KB for ftrace front-end. It **MUST** be a multiple of 4.
|
|
It's optional if you do not care console log.
|
|
|
|
Similar to oops front-end, there are multiple chunks for ftrace front-end
|
|
depending on the count of cpu processors. Each chunk size is equal to
|
|
ftrace_size / processors_count.
|
|
|
|
All log of ftrace will be appended to the chunk. On reboot the contents are
|
|
combined and available in */sys/fs/pstore/ftrace-pstore-blk-0*.
|
|
|
|
Persistent function tracing might be useful for debugging software or hardware
|
|
related hangs. Here is an example of usage::
|
|
|
|
# mount -t pstore pstore /sys/fs/pstore
|
|
# mount -t debugfs debugfs /sys/kernel/debug/
|
|
# echo 1 > /sys/kernel/debug/pstore/record_ftrace
|
|
# reboot -f
|
|
[...]
|
|
# mount -t pstore pstore /sys/fs/pstore
|
|
# tail /sys/fs/pstore/ftrace-pstore-blk-0
|
|
CPU:0 ts:5914676 c0063828 c0063b94 call_cpuidle <- cpu_startup_entry+0x1b8/0x1e0
|
|
CPU:0 ts:5914678 c039ecdc c006385c cpuidle_enter_state <- call_cpuidle+0x44/0x48
|
|
CPU:0 ts:5914680 c039e9a0 c039ecf0 cpuidle_enter_freeze <- cpuidle_enter_state+0x304/0x314
|
|
CPU:0 ts:5914681 c0063870 c039ea30 sched_idle_set_state <- cpuidle_enter_state+0x44/0x314
|
|
CPU:1 ts:5916720 c0160f59 c015ee04 kernfs_unmap_bin_file <- __kernfs_remove+0x140/0x204
|
|
CPU:1 ts:5916721 c05ca625 c015ee0c __mutex_lock_slowpath <- __kernfs_remove+0x148/0x204
|
|
CPU:1 ts:5916723 c05c813d c05ca630 yield_to <- __mutex_lock_slowpath+0x314/0x358
|
|
CPU:1 ts:5916724 c05ca2d1 c05ca638 __ww_mutex_lock <- __mutex_lock_slowpath+0x31c/0x358
|
|
|
|
max_reason
|
|
~~~~~~~~~~
|
|
|
|
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.
|
|
|
|
Configurations for driver
|
|
-------------------------
|
|
|
|
A device driver uses ``register_pstore_device`` with
|
|
``struct pstore_device_info`` to register to pstore/blk.
|
|
|
|
.. kernel-doc:: fs/pstore/blk.c
|
|
:export:
|
|
|
|
Compression and header
|
|
----------------------
|
|
|
|
Block device is large enough for uncompressed oops data. Actually we do not
|
|
recommend data compression because pstore/blk will insert some information into
|
|
the first line of oops/panic data. For example::
|
|
|
|
Panic: Total 16 times
|
|
|
|
It means that it's OOPS|Panic for the 16th time since the first booting.
|
|
Sometimes the number of occurrences of oops|panic since the first booting is
|
|
important to judge whether the system is stable.
|
|
|
|
The following line is inserted by pstore filesystem. For example::
|
|
|
|
Oops#2 Part1
|
|
|
|
It means that it's OOPS for the 2nd time on the last boot.
|
|
|
|
Reading the data
|
|
----------------
|
|
|
|
The dump data can be read from the pstore filesystem. The format for these
|
|
files is ``dmesg-pstore-blk-[N]`` for oops/panic front-end,
|
|
``pmsg-pstore-blk-0`` for pmsg front-end and so on. The timestamp of the
|
|
dump file records the trigger time. To delete a stored record from block
|
|
device, simply unlink the respective pstore file.
|
|
|
|
Attentions in panic read/write APIs
|
|
-----------------------------------
|
|
|
|
If on panic, the kernel is not going to run for much longer, the tasks will not
|
|
be scheduled and most kernel resources will be out of service. It
|
|
looks like a single-threaded program running on a single-core computer.
|
|
|
|
The following points require special attention for panic read/write APIs:
|
|
|
|
1. Can **NOT** allocate any memory.
|
|
If you need memory, just allocate while the block driver is initializing
|
|
rather than waiting until the panic.
|
|
#. Must be polled, **NOT** interrupt driven.
|
|
No task schedule any more. The block driver should delay to ensure the write
|
|
succeeds, but NOT sleep.
|
|
#. Can **NOT** take any lock.
|
|
There is no other task, nor any shared resource; you are safe to break all
|
|
locks.
|
|
#. Just use CPU to transfer.
|
|
Do not use DMA to transfer unless you are sure that DMA will not keep lock.
|
|
#. Control registers directly.
|
|
Please control registers directly rather than use Linux kernel resources.
|
|
Do I/O map while initializing rather than wait until a panic occurs.
|
|
#. Reset your block device and controller if necessary.
|
|
If you are not sure of the state of your block device and controller when
|
|
a panic occurs, you are safe to stop and reset them.
|
|
|
|
pstore/blk supports psblk_blkdev_info(), which is defined in
|
|
*linux/pstore_blk.h*, to get information of using block device, such as the
|
|
device number, sector count and start sector of the whole disk.
|
|
|
|
pstore block internals
|
|
----------------------
|
|
|
|
For developer reference, here are all the important structures and APIs:
|
|
|
|
.. kernel-doc:: fs/pstore/zone.c
|
|
:internal:
|
|
|
|
.. kernel-doc:: include/linux/pstore_zone.h
|
|
:internal:
|
|
|
|
.. kernel-doc:: include/linux/pstore_blk.h
|
|
:internal:
|