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Yoann Congal 08169cc8e1 printk: Fix LOG_CPU_MAX_BUF_SHIFT when BASE_SMALL is enabled 
[ Upstream commit 320bf43190 ]

LOG_CPU_MAX_BUF_SHIFT default value depends on BASE_SMALL:
  config LOG_CPU_MAX_BUF_SHIFT
  	default 12 if !BASE_SMALL
  	default 0 if BASE_SMALL
But, BASE_SMALL is a config of type int and "!BASE_SMALL" is always
evaluated to true whatever is the value of BASE_SMALL.

This patch fixes this by using the correct conditional operator for int
type : BASE_SMALL != 0.

Note: This changes CONFIG_LOG_CPU_MAX_BUF_SHIFT=12 to
CONFIG_LOG_CPU_MAX_BUF_SHIFT=0 for BASE_SMALL defconfigs, but that will
not be a big impact due to this code in kernel/printk/printk.c:
  /* by default this will only continue through for large > 64 CPUs */
  if (cpu_extra <= __LOG_BUF_LEN / 2)
          return;
Systems using CONFIG_BASE_SMALL and having 64+ CPUs should be quite
rare.

John Ogness <john.ogness@linutronix.de> (printk reviewer) wrote:
> For printk this will mean that BASE_SMALL systems were probably
> previously allocating/using the dynamic ringbuffer and now they will
> just continue to use the static ringbuffer. Which is fine and saves
> memory (as it should).

Petr Mladek <pmladek@suse.com> (printk maintainer) wrote:
> More precisely, it allocated the buffer dynamically when the sum
> of per-CPU-extra space exceeded half of the default static ring
> buffer. This happened for systems with more than 64 CPUs with
> the default config values.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Closes: https://lore.kernel.org/all/CAMuHMdWm6u1wX7efZQf=2XUAHascps76YQac6rdnQGhc8nop_Q@mail.gmail.com/
Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Closes: https://lore.kernel.org/all/f6856be8-54b7-0fa0-1d17-39632bf29ada@oracle.com/
Fixes: 4e244c10ea ("kconfig: remove unneeded symbol_empty variable")
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Yoann Congal <yoann.congal@smile.fr>
Link: https://lore.kernel.org/r/20240505080343.1471198-2-yoann.congal@smile.fr
Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2024-06-12 11:39:35 +02:00
..
.gitignore kbuild: build init/built-in.a just once 2022-09-29 04:40:15 +09:00
build-version kbuild: build init/built-in.a just once 2022-09-29 04:40:15 +09:00
calibrate.c
do_mounts.c init: flush async file closing 2024-02-08 18:41:03 +01:00
do_mounts.h init: flush async file closing 2024-02-08 18:41:03 +01:00
do_mounts_initrd.c init: pass root_device_name explicitly 2023-06-05 10:55:20 -06:00
do_mounts_rd.c init: add an init_unlink helper 2020-07-31 08:17:52 +02:00
init_task.c rcu-tasks: Initialize data to eliminate RCU-tasks/do_exit() deadlocks 2024-02-25 14:21:43 -08:00
initramfs.c init: open output files from cpio unpacking with O_LARGEFILE 2024-04-05 11:21:30 -07:00
Kconfig printk: Fix LOG_CPU_MAX_BUF_SHIFT when BASE_SMALL is enabled 2024-06-12 11:39:35 +02:00
main.c init/main.c: Fix potential static_command_line memory overflow 2024-04-13 00:59:36 +09:00
Makefile x86/retpoline: Make sure there are no unconverted return thunks due to KCSAN 2023-10-20 13:02:23 +02:00
noinitramfs.c init: move usermodehelper_enable() to populate_rootfs() 2021-09-08 11:50:27 -07:00
version-timestamp.c init/version-timestamp.c: remove unneeded #include <linux/version.h> 2023-01-09 07:34:38 +09:00
version.c init/version.c: Replace strlcpy with strscpy 2023-09-22 09:50:56 -07:00