From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751924AbbLKNU7 (ORCPT ); Fri, 11 Dec 2015 08:20:59 -0500 Received: from mx2.suse.de ([195.135.220.15]:48205 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751118AbbLKNUy (ORCPT ); Fri, 11 Dec 2015 08:20:54 -0500 From: Petr Mladek To: akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org, Geert Uytterhoeven , Arnd Bergmann , jkosina@suse.com, pmladek@suse.com Subject: [PATCH v4 4/4] printk/nmi: Increase the size of NMI buffer and make it configurable Date: Fri, 11 Dec 2015 14:20:52 +0100 Message-Id: <1449840052-10491-5-git-send-email-pmladek@suse.com> X-Mailer: git-send-email 1.8.5.6 In-Reply-To: <1449840052-10491-1-git-send-email-pmladek@suse.com> References: <1449840052-10491-1-git-send-email-pmladek@suse.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Testing has shown that the backtrace sometimes does not fit into the 4kB temporary buffer that is used in NMI context. The warnings are gone when I double the temporary buffer size. This patch doubles the buffer size and makes it configurable. Note that this problem existed even in the x86-specific implementation that was added by the commit a9edc8809328 ("x86/nmi: Perform a safe NMI stack trace on all CPUs"). Nobody noticed it because it did not print any warnings. Signed-off-by: Petr Mladek Cc: Jan Kara Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Russell King Cc: Daniel Thompson Cc: Jiri Kosina Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Ralf Baechle Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: David Miller Signed-off-by: Andrew Morton --- init/Kconfig | 22 ++++++++++++++++++++++ kernel/printk/nmi.c | 3 ++- 2 files changed, 24 insertions(+), 1 deletion(-) diff --git a/init/Kconfig b/init/Kconfig index c1c0b6a2d712..61cfd96a3c96 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -866,6 +866,28 @@ config LOG_CPU_MAX_BUF_SHIFT 13 => 8 KB for each CPU 12 => 4 KB for each CPU +config NMI_LOG_BUF_SHIFT + int "Temporary per-CPU NMI log buffer size (12 => 4KB, 13 => 8KB)" + range 10 21 + default 13 + depends on PRINTK_NMI + help + Select the size of a per-CPU buffer where NMI messages are temporary + stored. They are copied to the main log buffer in a safe context + to avoid a deadlock. The value defines the size as a power of 2. + + NMI messages are rare and limited. The largest one is when + a backtrace is printed. It usually fits into 4KB. Select + 8KB if you want to be on the safe side. + + Examples: + 17 => 128 KB for each CPU + 16 => 64 KB for each CPU + 15 => 32 KB for each CPU + 14 => 16 KB for each CPU + 13 => 8 KB for each CPU + 12 => 4 KB for each CPU + # # Architectures with an unreliable sched_clock() should select this: # diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c index d86f55cccf31..92c61e960c4a 100644 --- a/kernel/printk/nmi.c +++ b/kernel/printk/nmi.c @@ -41,7 +41,8 @@ DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default; static int printk_nmi_irq_ready; atomic_t nmi_message_lost; -#define NMI_LOG_BUF_LEN (4096 - sizeof(atomic_t) - sizeof(struct irq_work)) +#define NMI_LOG_BUF_LEN ((1 << CONFIG_NMI_LOG_BUF_SHIFT) - \ + sizeof(atomic_t) - sizeof(struct irq_work)) struct nmi_seq_buf { atomic_t len; /* length of written data */ -- 1.8.5.6