[PATCH next v3 00/15] printk: remove logbuf_lock

[John Ogness]

Hello,

Here is v3 of a series to remove @logbuf_lock, exposing the
ringbuffer locklessly to both readers and writers. v2 is here [0].

Since @logbuf_lock was protecting much more than just the
ringbuffer, this series clarifies and cleans up the various
protections using comments, lockless accessors, atomic types, and a
new finer-grained @syslog_lock.

Removing @logbuf_lock required changing the semantics of the
kmsg_dumper callback in order to work locklessly. Since this
involved touching all the kmsg_dump users, we also decided [1] to
use this opportunity to clean up and clarify the kmsg_dump semantics
in general.

This series is based on next-20210225.

Changes since v2:

- use get_maintainer.pl to get the full list of developers that
  should at least see the changes in their respective areas

- do not disable interrupts in arch/um kmsg_dumper (because there is
  no need to)

- protect the mtd/mtdoops kmsg_dumper buffer against concurrent
  dumps

- update kerneldoc for kmsg_dump_get_line() (@len_out)

- remove ksmg_dump's @active flag

- change kmsg_dumper callback to:
  void (*dump)(enum kmsg_dump_reason reason);

- rename kmsg_dumper_iter to kmsg_dump_iter

- update kmsg_dumpers to use their own kmsg_dump_iter (and
  initialize it with kmsg_dump_rewind() if necessary)

John Ogness

[0] https://lkml.kernel.org/r/20210218081817.28849-1-john.ogness@xxxxxxxxxxxxx
[1] https://lkml.kernel.org/r/YDeZAA08NKCHa4s%2F@alley

John Ogness (15):
  um: synchronize kmsg_dumper
  mtd: mtdoops: synchronize kmsg_dumper
  printk: limit second loop of syslog_print_all
  printk: kmsg_dump: remove unused fields
  printk: refactor kmsg_dump_get_buffer()
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: introduce CONSOLE_LOG_MAX for improved multi-line support
  printk: use seqcount_latch for clear_seq
  printk: use atomic64_t for devkmsg_user.seq
  printk: add syslog_lock
  printk: kmsg_dumper: remove @active field
  printk: introduce a kmsg_dump iterator
  printk: remove logbuf_lock
  printk: kmsg_dump: remove _nolock() variants
  printk: console: remove unnecessary safe buffer usage

 arch/powerpc/kernel/nvram_64.c             |  14 +-
 arch/powerpc/platforms/powernv/opal-kmsg.c |   3 +-
 arch/powerpc/xmon/xmon.c                   |   6 +-
 arch/um/kernel/kmsg_dump.c                 |  15 +-
 drivers/hv/vmbus_drv.c                     |   7 +-
 drivers/mtd/mtdoops.c                      |  20 +-
 fs/pstore/platform.c                       |   8 +-
 include/linux/kmsg_dump.h                  |  49 +--
 kernel/debug/kdb/kdb_main.c                |  10 +-
 kernel/printk/internal.h                   |   4 +-
 kernel/printk/printk.c                     | 456 ++++++++++-----------
 kernel/printk/printk_safe.c                |  27 +-
 12 files changed, 309 insertions(+), 310 deletions(-)

-- 
2.20.1