From: AKIYAMA Nobuyuki <akiyama.nobuyuk@jp.fujitsu.com>
-Summary
I made a patch for debugging with the help of NMI trigger switch. When
kernel hangs severely, keyboard operation(e.g.Ctrl-Alt-Del) doesn't work
properly. This patch enables debugging information to be displayed on
console in this case. I think this feature is necessary as standard
functionality.
-Background
When a trouble occurs in kernel, we usually begin to investigate with
following information:
- panic >> panic message.
- oops >> CPU registers and stack trace.
- hang >> **NONE** no standard method established.
-How it works
Most IA32 servers have a NMI switch that fires NMI interrupt up. The
NMI interrupt can interrupt even if kernel is serious state, for example
deadlock under the interrupt disabled. When the NMI switch is pressed
after this feature is activated, CPU registers and stack trace are
displayed on console and then panic occurs. This feature is activated or
deactivated with sysctl.
On IA32 architecture, only the following are defined as reason of NMI
interrupt:
- memory parity error
- I/O check error
The reason code of NMI switch is not defined, so this patch assumes that
all undefined NMI interrupts are fired by MNI switch. However, oprofile
and NMI watchdog also use undefined NMI interrupt. Therefore this feature
cannot be used at the same time with oprofile and NMI watchdog. This
feature hands NMI interrupt over to oprofile and NMI watchdog. So, when
they have been activated, this feature doesn't work even if it is
activated.
-Setup
Set up the system control parameter as follows:
# sysctl -w kernel.unknown_nmi_panic=1
kernel.unknown_nmi_panic = 1
If the NMI switch is pressed, CPU registers and stack trace will be
displayed on console and then panic occurs.
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/Documentation/filesystems/proc.txt | 14 ++++++
25-akpm/arch/i386/kernel/nmi.c | 64 +++++++++++++++++++++--------
25-akpm/arch/i386/kernel/traps.c | 21 +++++++++
25-akpm/include/linux/sysctl.h | 1
25-akpm/kernel/sysctl.c | 16 +++++++
5 files changed, 99 insertions(+), 17 deletions(-)
diff -puN arch/i386/kernel/nmi.c~nmi-trigger-switch-support-for-debugging arch/i386/kernel/nmi.c
--- 25/arch/i386/kernel/nmi.c~nmi-trigger-switch-support-for-debugging 2004-05-27 01:49:03.006069648 -0700
+++ 25-akpm/arch/i386/kernel/nmi.c 2004-05-27 01:49:53.599378296 -0700
@@ -25,13 +25,17 @@
#include <linux/module.h>
#include <linux/nmi.h>
#include <linux/sysdev.h>
+#include <linux/sysctl.h>
#include <asm/smp.h>
#include <asm/mtrr.h>
#include <asm/mpspec.h>
#include <asm/nmi.h>
+#include "mach_traps.h"
+
unsigned int nmi_watchdog = NMI_NONE;
+int unknown_nmi_panic;
static unsigned int nmi_hz = HZ;
static unsigned int nmi_perfctr_msr; /* the MSR to reset in NMI handler */
static unsigned int nmi_p4_cccr_val;
@@ -426,8 +430,6 @@ void setup_apic_nmi_watchdog (void)
nmi_active = 1;
}
-static spinlock_t nmi_print_lock = SPIN_LOCK_UNLOCKED;
-
/*
* the best way to detect whether a CPU has a 'hard lockup' problem
* is to check it's local APIC timer IRQ counts. If they are not
@@ -459,6 +461,8 @@ void touch_nmi_watchdog (void)
alert_counter[i] = 0;
}
+extern void die_nmi(struct pt_regs *, const char *msg);
+
void nmi_watchdog_tick (struct pt_regs * regs)
{
@@ -477,21 +481,8 @@ void nmi_watchdog_tick (struct pt_regs *
* wait a few IRQs (5 seconds) before doing the oops ...
*/
alert_counter[cpu]++;
- if (alert_counter[cpu] == 5*nmi_hz) {
- spin_lock(&nmi_print_lock);
- /*
- * We are in trouble anyway, lets at least try
- * to get a message out.
- */
- bust_spinlocks(1);
- printk("NMI Watchdog detected LOCKUP on CPU%d, eip %08lx, registers:\n", cpu, regs->eip);
- show_registers(regs);
- printk("console shuts up ...\n");
- console_silent();
- spin_unlock(&nmi_print_lock);
- bust_spinlocks(0);
- do_exit(SIGSEGV);
- }
+ if (alert_counter[cpu] == 5*nmi_hz)
+ die_nmi(regs, "NMI Watchdog detected LOCKUP");
} else {
last_irq_sums[cpu] = sum;
alert_counter[cpu] = 0;
@@ -518,6 +509,45 @@ void nmi_watchdog_tick (struct pt_regs *
}
}
+static int unknown_nmi_panic_callback(struct pt_regs *regs, int cpu)
+{
+ unsigned char reason = get_nmi_reason();
+ char buf[64];
+
+ if (!(reason & 0xc0)) {
+ sprintf(buf, "NMI received for unknown reason %02x\n", reason);
+ die_nmi(regs, buf);
+ }
+ return 0;
+}
+
+/*
+ * proc handler for /proc/sys/kernel/unknown_nmi_panic
+ */
+int proc_unknown_nmi_panic(ctl_table *table, int write,
+ struct file *file, void __user *buffer, size_t *length)
+{
+ int old_state;
+
+ old_state = unknown_nmi_panic;
+ proc_dointvec(table, write, file, buffer, length);
+ if (!!old_state == !!unknown_nmi_panic)
+ return 0;
+
+ if (unknown_nmi_panic) {
+ if (reserve_lapic_nmi() < 0) {
+ unknown_nmi_panic = 0;
+ return -EBUSY;
+ } else {
+ set_nmi_callback(unknown_nmi_panic_callback);
+ }
+ } else {
+ release_lapic_nmi();
+ unset_nmi_callback();
+ }
+ return 0;
+}
+
EXPORT_SYMBOL(nmi_active);
EXPORT_SYMBOL(nmi_watchdog);
EXPORT_SYMBOL(reserve_lapic_nmi);
diff -puN arch/i386/kernel/traps.c~nmi-trigger-switch-support-for-debugging arch/i386/kernel/traps.c
--- 25/arch/i386/kernel/traps.c~nmi-trigger-switch-support-for-debugging 2004-05-27 01:49:03.008069344 -0700
+++ 25-akpm/arch/i386/kernel/traps.c 2004-05-27 01:49:03.021067368 -0700
@@ -497,6 +497,27 @@ static void unknown_nmi_error(unsigned c
printk("Do you have a strange power saving mode enabled?\n");
}
+static spinlock_t nmi_print_lock = SPIN_LOCK_UNLOCKED;
+
+void die_nmi (struct pt_regs *regs, const char *msg)
+{
+ spin_lock(&nmi_print_lock);
+ /*
+ * We are in trouble anyway, lets at least try
+ * to get a message out.
+ */
+ bust_spinlocks(1);
+ printk(msg);
+ printk(" on CPU%d, eip %08lx, registers:\n",
+ smp_processor_id(), regs->eip);
+ show_registers(regs);
+ printk("console shuts up ...\n");
+ console_silent();
+ spin_unlock(&nmi_print_lock);
+ bust_spinlocks(0);
+ do_exit(SIGSEGV);
+}
+
static void default_do_nmi(struct pt_regs * regs)
{
unsigned char reason = get_nmi_reason();
diff -puN Documentation/filesystems/proc.txt~nmi-trigger-switch-support-for-debugging Documentation/filesystems/proc.txt
--- 25/Documentation/filesystems/proc.txt~nmi-trigger-switch-support-for-debugging 2004-05-27 01:49:03.010069040 -0700
+++ 25-akpm/Documentation/filesystems/proc.txt 2004-05-27 01:49:03.018067824 -0700
@@ -1109,6 +1109,20 @@ modprobe
The location where the modprobe binary is located. The kernel uses this
program to load modules on demand.
+unknown_nmi_panic
+-----------------
+
+The value in this file affects behavior of handling NMI. When the value is
+non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
+debugging information is displayed on console.
+
+NMI switch that most IA32 servers have fires unknown NMI up, for example.
+If a system hangs up, try pressing the NMI switch.
+
+[NOTE]
+ This function and oprofile share a NMI callback. Therefore this function
+ cannot be enabled when oprofile is activated.
+
2.4 /proc/sys/vm - The virtual memory subsystem
-----------------------------------------------
diff -puN include/linux/sysctl.h~nmi-trigger-switch-support-for-debugging include/linux/sysctl.h
--- 25/include/linux/sysctl.h~nmi-trigger-switch-support-for-debugging 2004-05-27 01:49:03.011068888 -0700
+++ 25-akpm/include/linux/sysctl.h 2004-05-27 01:49:03.022067216 -0700
@@ -133,6 +133,7 @@ enum
KERN_NGROUPS_MAX=63, /* int: NGROUPS_MAX */
KERN_SPARC_SCONS_PWROFF=64, /* int: serial console power-off halt */
KERN_HZ_TIMER=65, /* int: hz timer on or off */
+ KERN_UNKNOWN_NMI_PANIC=66, /* int: unknown nmi panic flag */
};
diff -puN kernel/sysctl.c~nmi-trigger-switch-support-for-debugging kernel/sysctl.c
--- 25/kernel/sysctl.c~nmi-trigger-switch-support-for-debugging 2004-05-27 01:49:03.013068584 -0700
+++ 25-akpm/kernel/sysctl.c 2004-05-27 01:49:03.060061440 -0700
@@ -65,6 +65,12 @@ extern int min_free_kbytes;
extern int printk_ratelimit_jiffies;
extern int printk_ratelimit_burst;
+#if defined(__i386__)
+extern int unknown_nmi_panic;
+extern int proc_unknown_nmi_panic(ctl_table *, int, struct file *,
+ void __user *, size_t *);
+#endif
+
/* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
static int maxolduid = 65535;
static int minolduid;
@@ -636,6 +642,16 @@ static ctl_table kern_table[] = {
.mode = 0444,
.proc_handler = &proc_dointvec,
},
+#if defined(__i386__)
+ {
+ .ctl_name = KERN_UNKNOWN_NMI_PANIC,
+ .procname = "unknown_nmi_panic",
+ .data = &unknown_nmi_panic,
+ .maxlen = sizeof (int),
+ .mode = 0644,
+ .proc_handler = &proc_unknown_nmi_panic,
+ },
+#endif
{ .ctl_name = 0 }
};
_