[GIT PULL] printk for 5.10 (includes lockless ringbuffer)

From: Petr Mladek
Date: Mon Oct 12 2020 - 10:49:21 EST


please pull the latest printk changes from

git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux tags/printk-for-5.10


- 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@xxxxxxxxxxxxx. 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.


The fully lockless ringbuffer code has been tested in linux-next
since Jul 10. The pr_cont() handling has been pushed in Sep 15.
I am not aware of any regression at the moment. But of course,
there will be some. And we are ready to work on the fixes.

Andy Shevchenko (1):
kernel.h: Move oops_in_progress to printk.h

Gustavo A. R. Silva (1):
printk: Use fallthrough pseudo-keyword

John Ogness (22):
crash: add VMCOREINFO macro to define offset in a struct declared by typedef
printk: add lockless ringbuffer
Revert "printk: lock/unlock console only for new logbuf entries"
printk: use the lockless ringbuffer
printk: ringbuffer: support dataless records
printk: reduce LOG_BUF_SHIFT range for H8300
docs: vmcoreinfo: add lockless printk ringbuffer vmcoreinfo
scripts/gdb: add utils.read_ulong()
scripts/gdb: update for lockless printk ringbuffer
printk: ringbuffer: fix setting state in desc_read()
printk: ringbuffer: avoid memcpy() on state_var
printk: ringbuffer: relocate get_data()
printk: ringbuffer: add BLK_DATALESS() macro
printk: ringbuffer: clear initial reserved fields
printk: ringbuffer: change representation of states
printk: ringbuffer: add finalization/extension support
printk: reimplement log_cont using record extension
printk: move printk_info into separate array
printk: move dictionary keys to dev_printk_info
printk: remove dict ring
printk: avoid and/or handle record truncation
printk: reduce setup_text_buf size to LOG_LINE_MAX

Petr Mladek (2):
MAINTAIERS: Add John Ogness as printk reviewer
Merge branch 'printk-rework' into for-linus

Randy Dunlap (1):
kernel: printk: delete repeated words in comments

Sergey Senozhatsky (1):
serial: 8250: change lock order in serial8250_do_startup()

Documentation/admin-guide/kdump/gdbmacros.txt | 159 +-
Documentation/admin-guide/kdump/vmcoreinfo.rst | 131 +-
drivers/base/core.c | 46 +-
drivers/tty/serial/8250/8250_port.c | 9 +-
include/linux/crash_core.h | 3 +
include/linux/debug_locks.h | 2 +-
include/linux/dev_printk.h | 8 +
include/linux/kernel.h | 1 -
include/linux/printk.h | 8 +-
init/Kconfig | 3 +-
kernel/printk/Makefile | 1 +
kernel/printk/internal.h | 4 +-
kernel/printk/printk.c | 1153 +++++++------
kernel/printk/printk_ringbuffer.c | 2083 ++++++++++++++++++++++++
kernel/printk/printk_ringbuffer.h | 382 +++++
kernel/printk/printk_safe.c | 2 +-
scripts/gdb/linux/dmesg.py | 147 +-
scripts/gdb/linux/utils.py | 7 +
19 files changed, 3416 insertions(+), 734 deletions(-)
create mode 100644 kernel/printk/printk_ringbuffer.c
create mode 100644 kernel/printk/printk_ringbuffer.h