linux-kernel - [PATCH v2 5/5] printk/nmi: Increase the size of the temporary buffer

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Date:	Fri, 27 Nov 2015 12:09:32 +0100
From:	Petr Mladek <pmladek@...e.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	Jiri Kosina <jkosina@...e.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-arm-kernel@...ts.infradead.org,
	adi-buildroot-devel@...ts.sourceforge.net,
	linux-cris-kernel@...s.com, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>
Subject: [PATCH v2 5/5] printk/nmi: Increase the size of the temporary buffer

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.

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@...e.com>
---
 kernel/printk/nmi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c
index 8af1e4016719..6111644d5f01 100644
--- a/kernel/printk/nmi.c
+++ b/kernel/printk/nmi.c
@@ -42,7 +42,7 @@ atomic_t nmi_message_lost;
 struct nmi_seq_buf {
 	atomic_t		len;	/* length of written data */
 	struct irq_work		work;	/* IRQ work that flushes the buffer */
-	unsigned char		buffer[PAGE_SIZE - sizeof(atomic_t) -
+	unsigned char		buffer[2 * PAGE_SIZE - sizeof(atomic_t) -
 				       sizeof(struct irq_work)];
 };
 static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
-- 
1.8.5.6

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