Received-SPF: pass (google.com: domain of linux-kernel+bounces-168914-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
From: yoann.congal@smile.fr
To: linux-fsdevel@vger.kernel.org,
	linux-kbuild@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-serial@vger.kernel.org,
	x86@kernel.org
Cc: =?UTF-8?q?Andr=C3=A9=20Almeida?= <andrealmeid@igalia.com>,
	Borislav Petkov <bp@alien8.de>,
	Darren Hart <dvhart@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Ingo Molnar <mingo@redhat.com>,
	Jiri Slaby <jirislaby@kernel.org>,
	John Ogness <john.ogness@linutronix.de>,
	Josh Triplett <josh@joshtriplett.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	Yoann Congal <yoann.congal@smile.fr>,
	Vegard Nossum <vegard.nossum@oracle.com>
Subject: [PATCH RESEND v6 1/3] printk: Fix LOG_CPU_MAX_BUF_SHIFT when BASE_SMALL is enabled
Date: Sun,  5 May 2024 10:03:41 +0200
Message-Id: <20240505080343.1471198-2-yoann.congal@smile.fr>
In-Reply-To: <20240505080343.1471198-1-yoann.congal@smile.fr>
References: <20240505080343.1471198-1-yoann.congal@smile.fr>
Precedence: bulk
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit

From: Yoann Congal <yoann.congal@smile.fr>

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: 4e244c10eab3 ("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>
---
 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
 	help
 	  This option allows to increase the default ring buffer size
-- 
2.39.2