| Message ID | 1449667265-17525-5-git-send-email-pmladek@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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
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 */
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(-)