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

John Ogness
2021-02-25T20:24:23Z

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@linutronix.de
[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