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printk/nmi: increase the size of NMI buffer and make it configurable

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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 a9edc88093 ("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 <rmk+kernel@arm.linux.org.uk>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jiri Kosina <jkosina@suse.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: David Miller <davem@davemloft.net>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Petr Mladek 2016-05-20 17:00:39 -07:00 committed by Linus Torvalds
parent b522deabc6
commit 427934b871
2 changed files with 24 additions and 1 deletions
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22
init/Kconfig
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@ -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:
#

3
kernel/printk/nmi.c
View File

@ -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 */