[PATCH next v4 00/15] printk: remove logbuf_lock

[John Ogness]

Hello,

Here is v4 of a series to remove @logbuf_lock, exposing the
ringbuffer locklessly to both readers and writers. v3 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. This series
adjusts all kmsg_dumpers and users of the kmsg_dump_get_*()
functions for the new semantics.

This series is based on next-20210303.

Changes since v3:

- disable interrupts in the arch/um kmsg_dumper

- reduce CONSOLE_LOG_MAX value from 4096 back to 1024 to revert
  the increasd 3KiB static memory footprint

- change the kmsg_dumper() callback prototype back to how it
  was because some dumpers need the registered object for
  container_of() usage

- for kmsg_dump_get_line()/kmsg_dump_get_buffer() restrict the
  minimal allowed sequence number to the cleared sequence number

John Ogness

[0] https://lore.kernel.org/lkml/20210225202438.28985-1-john.ogness@xxxxxxxxxxxxx/

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
  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 |   8 +-
 arch/powerpc/xmon/xmon.c       |   6 +-
 arch/um/kernel/kmsg_dump.c     |  13 +-
 drivers/hv/vmbus_drv.c         |   4 +-
 drivers/mtd/mtdoops.c          |  17 +-
 fs/pstore/platform.c           |   5 +-
 include/linux/kmsg_dump.h      |  47 ++--
 kernel/debug/kdb/kdb_main.c    |  10 +-
 kernel/printk/internal.h       |   4 +-
 kernel/printk/printk.c         | 464 +++++++++++++++++----------------
 kernel/printk/printk_safe.c    |  27 +-
 11 files changed, 310 insertions(+), 295 deletions(-)

-- 
2.20.1