[PATCH RESEND v6 1/3] printk: Fix LOG_CPU_MAX_BUF_SHIFT when BASE_SMALL is enabled

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From: Yoann Congal <yoann.congal@xxxxxxxx>

LOG_CPU_MAX_BUF_SHIFT default value depends on BASE_SMALL:
  	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)
Systems using CONFIG_BASE_SMALL and having 64+ CPUs should be quite

John Ogness <john.ogness@xxxxxxxxxxxxx> (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@xxxxxxxx> (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@xxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/all/CAMuHMdWm6u1wX7efZQf=2XUAHascps76YQac6rdnQGhc8nop_Q@xxxxxxxxxxxxxx/
Reported-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Closes: https://lore.kernel.org/all/f6856be8-54b7-0fa0-1d17-39632bf29ada@xxxxxxxxxx/
Fixes: 4e244c10eab3 ("kconfig: remove unneeded symbol_empty variable")
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Reviewed-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Signed-off-by: Yoann Congal <yoann.congal@xxxxxxxx>
 init/Kconfig | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 8426d59cc634d..ad4b6f778d2bd 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -743,8 +743,8 @@ config LOG_CPU_MAX_BUF_SHIFT
 	int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
 	depends on SMP
 	range 0 21
-	default 12 if !BASE_SMALL
-	default 0 if BASE_SMALL
+	default 0 if BASE_SMALL != 0
+	default 12
 	depends on PRINTK
 	  This option allows to increase the default ring buffer size

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