linux-toradex.git/Documentation/admin-guide/kdump, branch v5.17-rc4

Documentation: kdump: update kdump guide

2021-06-14T14:12:01+00:00

Some parts of the guide are aged, hence need be updated.

1) The backup area of the 1st 640K on X86_64 has been removed
   by below commits, update the description accordingly.

   commit 7c321eb2b843 ("x86/kdump: Remove the backup region handling")
   commit 6f599d84231f ("x86/kdump: Always reserve the low 1M when the crashkernel option is specified")

2) Sort out the descripiton of "crashkernel syntax" part.

3) And some other minor cleanups.

Signed-off-by: Baoquan He 
Acked-by: Dave Young 
Link: https://lore.kernel.org/r/20210609083218.GB591017@MiWiFi-R3L-srv
[jc: added blank line to fix added build warning]
Signed-off-by: Jonathan Corbet

kdump: append uts_namespace.name offset to VMCOREINFO

2020-12-16T06:46:18+00:00

The offset of the field 'init_uts_ns.name' has changed since commit
9a56493f6942 ("uts: Use generic ns_common::count").

Make the offset of the field 'uts_namespace.name' available in VMCOREINFO
because tools like 'crash-utility' and 'makedumpfile' must be able to read
it from crash dumps.

Link: https://lore.kernel.org/r/159644978167.604812.1773586504374412107.stgit@localhost.localdomain
Link: https://lkml.kernel.org/r/20200930102328.396488-1-egorenar@linux.ibm.com
Signed-off-by: Alexander Egorenkov 
Acked-by: lijiang 
Acked-by: Baoquan He 
Cc: Dave Young 
Cc: Vivek Goyal 
Cc: "Eric W . Biederman" 
Cc: Kirill Tkhai 
Cc: Kees Cook 
Cc: Christian Brauner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Merge tag 'printk-for-5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

2020-10-13T22:58:10+00:00

Pull printk updates from Petr Mladek:
"The big new thing is the fully lockless ringbuffer implementation,
including the support for continuous lines. It will allow to store and
read messages in any situation wihtout the risk of deadlocks and
without the need of temporary per-CPU buffers.

The access is still serialized by logbuf_lock. It synchronizes few
more operations, for example, temporary buffer for formatting the
message, syslog and kmsg_dump operations. The lock removal is being
discussed and should be ready for the next release.

The continuous lines are handled exactly the same way as before to
avoid regressions in user space. It means that they are appended to
the last message when the caller is the same. Only the last message
can be extended.

The data ring includes plain text of the messages. Except for an
integer at the beginning of each message that points back to the
descriptor ring with other metadata.

The dictionary has to stay. journalctl uses it to filter the log. It
allows to show messages related to a given device. The dictionary
values are stored in the descriptor ring with the other metadata.

This is the first part of the printk rework as discussed at Plumbers
2019, see https://lore.kernel.org/r/87k1acz5rx.fsf@linutronix.de. The
next big step will be handling consoles by kthreads during the normal
system operation. It will require special handling of situations when
the kthreads could not get scheduled, for example, early boot,
suspend, panic.

Other changes:

- Add John Ogness as a reviewer for printk subsystem. He is author of
the rework and is familiar with the code and history.

- Fix locking in serial8250_do_startup() to prevent lockdep report.

- Few code cleanups"

* tag 'printk-for-5.10' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (27 commits)
printk: Use fallthrough pseudo-keyword
printk: reduce setup_text_buf size to LOG_LINE_MAX
printk: avoid and/or handle record truncation
printk: remove dict ring
printk: move dictionary keys to dev_printk_info
printk: move printk_info into separate array
printk: reimplement log_cont using record extension
printk: ringbuffer: add finalization/extension support
printk: ringbuffer: change representation of states
printk: ringbuffer: clear initial reserved fields
printk: ringbuffer: add BLK_DATALESS() macro
printk: ringbuffer: relocate get_data()
printk: ringbuffer: avoid memcpy() on state_var
printk: ringbuffer: fix setting state in desc_read()
kernel.h: Move oops_in_progress to printk.h
scripts/gdb: update for lockless printk ringbuffer
scripts/gdb: add utils.read_ulong()
docs: vmcoreinfo: add lockless printk ringbuffer vmcoreinfo
printk: reduce LOG_BUF_SHIFT range for H8300
printk: ringbuffer: support dataless records
...

Merge branch 'printk-rework' into for-linus

2020-10-12T11:01:37+00:00

docs: admin-guide: update kdump documentation due to change of crash URL

2020-09-24T16:43:07+00:00

Since crash utility has been moved to github, the original URL is no
longer available. Let's update it accordingly.

Suggested-by: Dave Young 
Signed-off-by: Lianbo Jiang 
Link: https://lore.kernel.org/r/a088bff5-1174-25fa-ac26-6e46795f4085@redhat.com
Signed-off-by: Jonathan Corbet

printk: move dictionary keys to dev_printk_info

2020-09-22T09:27:48+00:00

Dictionaries are only used for SUBSYSTEM and DEVICE properties. The
current implementation stores the property names each time they are
used. This requires more space than otherwise necessary. Also,
because the dictionary entries are currently considered optional,
it cannot be relied upon that they are always available, even if the
writer wanted to store them. These issues will increase should new
dictionary properties be introduced.

Rather than storing the subsystem and device properties in the
dict ring, introduce a struct dev_printk_info with separate fields
to store only the property values. Embed this struct within the
struct printk_info to provide guaranteed availability.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/87mu1jl6ne.fsf@jogness.linutronix.de

printk: ringbuffer: add finalization/extension support

2020-09-15T14:35:27+00:00

Add support for extending the newest data block. For this, introduce
a new finalization state (desc_finalized) denoting a committed
descriptor that cannot be extended.

Until a record is finalized, a writer can reopen that record to
append new data. Reopening a record means transitioning from the
desc_committed state back to the desc_reserved state.

A writer can explicitly finalize a record if there is no intention
of extending it. Also, records are automatically finalized when a
new record is reserved. This relieves writers of needing to
explicitly finalize while also making such records available to
readers sooner. (Readers can only traverse finalized records.)

Four new memory barrier pairs are introduced. Two of them are
insignificant additions (data_realloc:A/desc_read:D and
data_realloc:A/data_push_tail:B) because they are alternate path
memory barriers that exactly match the purpose, pairing, and
context of the two existing memory barrier pairs they provide an
alternate path for. The other two new memory barrier pairs are
significant additions:

desc_reopen_last:A / _prb_commit:B - When reopening a descriptor,
    ensure the state transitions back to desc_reserved before
    fully trusting the descriptor data.

_prb_commit:B / desc_reserve:D - When committing a descriptor,
    ensure the state transitions to desc_committed before checking
    the head ID to see if the descriptor needs to be finalized.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20200914123354.832-6-john.ogness@linutronix.de

printk: ringbuffer: change representation of states

2020-09-15T13:52:49+00:00

Rather than deriving the state by evaluating bits within the flags
area of the state variable, assign the states explicit values and
set those values in the flags area. Introduce macros to make it
simple to read and write state values for the state variable.

Although the functionality is preserved, the binary representation
for the states is changed.

Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20200914123354.832-5-john.ogness@linutronix.de

scripts/gdb: update for lockless printk ringbuffer

2020-09-08T07:33:15+00:00

With the introduction of the lockless printk ringbuffer, the data
structure for the kernel log buffer was changed. Update the gdb
scripts to be able to parse/print the new log buffer structure.

Fixes: 896fbe20b4e2333fb55 ("printk: use the lockless ringbuffer")
Signed-off-by: John Ogness 
Reported-by: Nick Desaulniers 
Tested-by: Nick Desaulniers 
Tested-by: Petr Mladek 
[akpm@linux-foundation.org: A typo fix.]
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20200814212525.6118-3-john.ogness@linutronix.de

docs: vmcoreinfo: add lockless printk ringbuffer vmcoreinfo

2020-09-08T07:33:15+00:00

With the introduction of the lockless printk ringbuffer, the
VMCOREINFO relating to the kernel log buffer was changed. Update the
documentation to match those changes.

Fixes: 896fbe20b4e2333fb55 ("printk: use the lockless ringbuffer")
Reported-by: Nick Desaulniers 
Signed-off-by: John Ogness 
Reviewed-by: Petr Mladek 
Signed-off-by: Petr Mladek 
Link: https://lore.kernel.org/r/20200814213316.6394-1-john.ogness@linutronix.de