diff mbox

[v3,4/4] printk/nmi: Increase the size of NMI buffer and make it configurable

Message ID 1449667265-17525-5-git-send-email-pmladek@suse.com (mailing list archive)
State Not Applicable
Delegated to: Simon Horman
Headers show

Commit Message

Petr Mladek Dec. 9, 2015, 1:21 p.m. UTC
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>
---
 init/Kconfig        | 22 ++++++++++++++++++++++
 kernel/printk/nmi.c |  3 ++-
 2 files changed, 24 insertions(+), 1 deletion(-)

Comments

Geert Uytterhoeven Dec. 11, 2015, 11:10 a.m. UTC | #1
On Wed, Dec 9, 2015 at 2:21 PM, Petr Mladek <pmladek@suse.com> wrote:
> --- 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 && HAVE_NMI

Symbol NMI_LOG_BUF_SHIFT does not exist if its dependencies are not met.

> +       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 5465230b75ec..78c07d441b4e 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))

kernel/printk/nmi.c:50:24: error: 'CONFIG_NMI_LOG_BUF_SHIFT'
undeclared here (not in a function)

E.g. efm32_defconfig
http://kisskb.ellerman.id.au/kisskb/buildresult/12565754/

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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diff mbox

Patch

diff --git a/init/Kconfig b/init/Kconfig
index c1c0b6a2d712..efcff25a112d 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 && HAVE_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 5465230b75ec..78c07d441b4e 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 */