minix/kernel/start.c
Tomas Hruby 5efa92f754 NMI watchdog is an awesome feature for debugging locked up kernels.
There is not that much use for it on a single CPU, however, deadlock
between kernel and system task can be delected. Or a runaway loop.

If a kernel gets locked up the timer interrupts don't occure (as all
interrupts are disabled in kernel mode). The only chance is to
interrupt the kernel by a non-maskable interrupt.

This patch generates NMIs using performance counters. It uses the most
widely available performace counters. As the performance counters are 
highly model-specific this patch is not guaranteed to work on every
machine.  Unfortunately this is also true for KVM :-/ On the other
hand adding this feature for other models is not extremely difficult
and the framework makes it hopefully easy enough.

Depending on the frequency of the CPU an NMI is generated at most
about every 0.5s If the cpu's speed is less then 2Ghz it is generated
at most every 1s. In general an NMI is generated much less often as
the performance counter counts down only if the cpu is not idle.
Therefore the overhead of this feature is fairly minimal even if the
load is high.

Uppon detecting that the kernel is locked up the kernel dumps the 
state of the kernel registers and panics.

Local APIC must be enabled for the watchdog to work.

The code is _always_ compiled in, however, it is only enabled if  
watchdog=<non-zero> is set in the boot monitor.

One corner case is serial console debugging. As dumping a lot of stuff
to the serial link may take a lot of time, the watchdog does not 
detect lockups during this time!!! as it would result in too many
false positives. 10 nmi have to be handled before the lockup is
detected. This means something between ~5s to 10s.

Another corner case is that the watchdog is enabled only after the
paging is enabled as it would be pure madness to try to get it right.
2010-01-16 20:53:55 +00:00

126 lines
3.9 KiB
C

/* First C file used by the kernel. */
#include "kernel.h"
#include "proc.h"
#include <stdlib.h>
#include <string.h>
#include <archconst.h>
#include "proto.h"
#ifdef CONFIG_WATCHDOG
#include "watchdog.h"
#endif
FORWARD _PROTOTYPE( char *get_value, (_CONST char *params, _CONST char *key));
/*===========================================================================*
* cstart *
*===========================================================================*/
PUBLIC void cstart(cs, ds, mds, parmoff, parmsize)
U16_t cs, ds; /* kernel code and data segment */
U16_t mds; /* monitor data segment */
U16_t parmoff, parmsize; /* boot parameters offset and length */
{
/* Perform system initializations prior to calling main(). Most settings are
* determined with help of the environment strings passed by MINIX' loader.
*/
register char *value; /* value in key=value pair */
extern int etext, end;
int h;
/* Record where the kernel and the monitor are. */
kinfo.code_base = seg2phys(cs);
kinfo.code_size = (phys_bytes) &etext; /* size of code segment */
kinfo.data_base = seg2phys(ds);
kinfo.data_size = (phys_bytes) &end; /* size of data segment */
/* protection initialization */
prot_init();
/* Copy the boot parameters to the local buffer. */
arch_get_params(params_buffer, sizeof(params_buffer));
/* Record miscellaneous information for user-space servers. */
kinfo.nr_procs = NR_PROCS;
kinfo.nr_tasks = NR_TASKS;
strncpy(kinfo.release, OS_RELEASE, sizeof(kinfo.release));
kinfo.release[sizeof(kinfo.release)-1] = '\0';
strncpy(kinfo.version, OS_VERSION, sizeof(kinfo.version));
kinfo.version[sizeof(kinfo.version)-1] = '\0';
kinfo.proc_addr = (vir_bytes) proc;
/* Load average data initialization. */
kloadinfo.proc_last_slot = 0;
for(h = 0; h < _LOAD_HISTORY; h++)
kloadinfo.proc_load_history[h] = 0;
/* Processor? Decide if mode is protected for older machines. */
machine.processor=atoi(get_value(params_buffer, "processor"));
/* XT, AT or MCA bus? */
value = get_value(params_buffer, "bus");
if (value == NIL_PTR || strcmp(value, "at") == 0) {
machine.pc_at = TRUE; /* PC-AT compatible hardware */
} else if (strcmp(value, "mca") == 0) {
machine.pc_at = machine.ps_mca = TRUE; /* PS/2 with micro channel */
}
/* Type of VDU: */
value = get_value(params_buffer, "video"); /* EGA or VGA video unit */
if (strcmp(value, "ega") == 0) machine.vdu_ega = TRUE;
if (strcmp(value, "vga") == 0) machine.vdu_vga = machine.vdu_ega = TRUE;
/* Get clock tick frequency. */
value = get_value(params_buffer, "hz");
if(value)
system_hz = atoi(value);
if(!value || system_hz < 2 || system_hz > 50000) /* sanity check */
system_hz = DEFAULT_HZ;
value = get_value(params_buffer, SERVARNAME);
if(value && atoi(value) == 0)
do_serial_debug=1;
#ifdef CONFIG_APIC
value = get_value(params_buffer, "no_apic");
if(value)
config_no_apic = atoi(value);
else
config_no_apic = 1;
#endif
#ifdef CONFIG_WATCHDOG
value = get_value(params_buffer, "watchdog");
if (value)
watchdog_enabled = atoi(value);
#endif
/* Return to assembler code to switch to protected mode (if 286),
* reload selectors and call main().
*/
intr_init(INTS_MINIX, 0);
}
/*===========================================================================*
* get_value *
*===========================================================================*/
PRIVATE char *get_value(params, name)
_CONST char *params; /* boot monitor parameters */
_CONST char *name; /* key to look up */
{
/* Get environment value - kernel version of getenv to avoid setting up the
* usual environment array.
*/
register _CONST char *namep;
register char *envp;
for (envp = (char *) params; *envp != 0;) {
for (namep = name; *namep != 0 && *namep == *envp; namep++, envp++)
;
if (*namep == '\0' && *envp == '=') return(envp + 1);
while (*envp++ != 0)
;
}
return(NIL_PTR);
}