[PATCH v5 3/4] printk/nmi: increase the size of NMI buffer and make it configurable
From: pmladek@suse.com (Petr Mladek)
Date: 2016-04-21 11:49:54
Also in:
linux-mips, linux-sh, linuxppc-dev, lkml, sparclinux
Subsystem:
printk, the rest · Maintainers:
Petr Mladek, Linus Torvalds
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 <pmladek@suse.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Russell King <redacted>
Cc: Daniel Thompson <redacted>
Cc: Jiri Kosina <redacted>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <redacted>
Cc: Ralf Baechle <redacted>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <redacted>
Cc: David Miller <davem@davemloft.net>
Cc: Daniel Thompson <redacted>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
init/Kconfig | 22 ++++++++++++++++++++++
kernel/printk/nmi.c | 3 ++-
2 files changed, 24 insertions(+), 1 deletion(-)
diff --git a/init/Kconfig b/init/Kconfig
index 85c7a2bf1ea4..9dfd27394d43 100644
--- a/init/Kconfig
+++ b/init/Kconfig@@ -862,6 +862,28 @@ 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 572f94922230..bf08557d7e3d 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