FreeBSD/Linux Kernel Cross Reference
sys/x86/x86/mp_watchdog.c

     /*-
      * Copyright (c) 2004 Robert N. M. Watson
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     * $FreeBSD$
     */
    
    #include "opt_mp_watchdog.h"
    #include "opt_sched.h"
    
    #ifdef SCHED_ULE
    #error MP_WATCHDOG cannot currently be used with SCHED_ULE
    #endif
    
    #include <sys/param.h>
    #include <sys/kdb.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/pcpu.h>
    #include <sys/proc.h>
    #include <sys/sysctl.h>
    #include <sys/systm.h>
    
    #include <machine/smp.h>
    #include <x86/apicreg.h>
    #include <x86/apicvar.h>
    #include <machine/mp_watchdog.h>
    
    /*
     * mp_watchdog hijacks the idle thread on a specified CPU, prevents new work
     * from being scheduled there, and uses it as a "watchdog" to detect kernel
     * failure on other CPUs.  This is made reasonable by inclusion of logical
     * processors in Xeon hardware.  The watchdog is configured by setting the
     * debug.watchdog sysctl/tunable to the CPU of interest.  A callout will then
     * begin executing reseting a timer that is gradually lowered by the watching
     * thread.  If the timer reaches 0, the watchdog fires by ether dropping
     * directly to the debugger, or by sending an NMI IPI to the boot processor.
     * This is a somewhat less efficient substitute for dedicated watchdog
     * hardware, but can be quite an effective tool for debugging hangs.
     *
     * XXXRW: This should really use the watchdog(9)/watchdog(4) framework, but
     * doesn't yet.
     */
    static int      watchdog_cpu = -1;
    static int      watchdog_dontfire = 1;
    static int      watchdog_timer = -1;
    static int      watchdog_nmi = 1;
    
    SYSCTL_INT(_debug, OID_AUTO, watchdog_nmi, CTLFLAG_RWTUN, &watchdog_nmi, 0,
        "IPI the boot processor with an NMI to enter the debugger");
    
    static struct callout   watchdog_callout;
    
    static void watchdog_change(int wdcpu);
    
    /*
     * Number of seconds before the watchdog will fire if the callout fails to
     * reset the timer.
     */
    #define WATCHDOG_THRESHOLD      10
    
    static void
    watchdog_init(void *arg)
    {
    
            callout_init(&watchdog_callout, 1);
            if (watchdog_cpu != -1)
                    watchdog_change(watchdog_cpu);
    }
    
    /*
     * This callout resets a timer until the watchdog kicks in.  It acquires some
     * critical locks to make sure things haven't gotten wedged with those locks
     * held.
     */
    static void
    watchdog_function(void *arg)
   {
   
           /*
            * Since the timer ran, we must not be wedged.  Acquire some critical
            * locks to make sure.  Then reset the timer.
            */
           mtx_lock(&Giant);
           watchdog_timer = WATCHDOG_THRESHOLD;
           mtx_unlock(&Giant);
           callout_reset(&watchdog_callout, 1 * hz, watchdog_function, NULL);
   }
   SYSINIT(watchdog_init, SI_SUB_DRIVERS, SI_ORDER_ANY, watchdog_init, NULL);
   
   static void
   watchdog_change(int wdcpu)
   {
   
           if (wdcpu == -1 || wdcpu == 0xffffffff) {
                   /*
                    * Disable the watchdog.
                    */
                   watchdog_cpu = -1;
                   watchdog_dontfire = 1;
                   callout_stop(&watchdog_callout);
                   printf("watchdog stopped\n");
           } else {
                   watchdog_timer = WATCHDOG_THRESHOLD;
                   watchdog_dontfire = 0;
                   watchdog_cpu = wdcpu;
                   callout_reset(&watchdog_callout, 1 * hz, watchdog_function,
                       NULL);
           }
   }
   
   /*
    * This sysctl sets which CPU is the watchdog CPU.  Set to -1 or 0xffffffff
    * to disable the watchdog.
    */
   static int
   sysctl_watchdog(SYSCTL_HANDLER_ARGS)
   {
           int error, temp;
   
           temp = watchdog_cpu;
           error = sysctl_handle_int(oidp, &temp, 0, req);
           if (error)
                   return (error);
   
           if (req->newptr != NULL)
                   watchdog_change(temp);
           return (0);
   }
   SYSCTL_PROC(_debug, OID_AUTO, watchdog, CTLTYPE_INT|CTLFLAG_RW, 0, 0,
       sysctl_watchdog, "I", "");
   
   /*
    * Drop into the debugger by sending an IPI NMI to the boot processor.
    */
   static void
   watchdog_ipi_nmi(void)
   {
   
           /*
            * Deliver NMI to the boot processor.  Why not?
            */
           lapic_ipi_raw(APIC_DEST_DESTFLD | APIC_TRIGMOD_EDGE |
               APIC_LEVEL_ASSERT | APIC_DESTMODE_PHY | APIC_DELMODE_NMI,
               boot_cpu_id);
           lapic_ipi_wait(-1);
   }
   
   /*
    * ap_watchdog() is called by the SMP idle loop code.  It works on the same
    * premise that the disabling of logical processors does: that if the cpu is
    * idle, then it can ignore the world from then on, as nothing will be
    * scheduled on it.  Leaving aside multi-runqueue schedulers (SCHED_ULE) and
    * explicit process migration (sched_bind()), this is not an unreasonable
    * assumption.
    */
   void
   ap_watchdog(u_int cpuid)
   {
           char old_pcomm[MAXCOMLEN + 1];
           struct proc *p;
   
           if (watchdog_cpu != cpuid)
                   return;
   
           printf("watchdog started on cpu %d\n", cpuid);
           p = curproc;
           bcopy(p->p_comm, old_pcomm, MAXCOMLEN + 1);
           snprintf(p->p_comm, MAXCOMLEN + 1, "mp_watchdog cpu %d", cpuid);
           while (1) {
                   DELAY(1000000);                         /* One second. */
                   if (watchdog_cpu != cpuid)
                           break;
                   atomic_subtract_int(&watchdog_timer, 1);
                   if (watchdog_timer < 4)
                           printf("Watchdog timer: %d\n", watchdog_timer);
                   if (watchdog_timer == 0 && watchdog_dontfire == 0) {
                           printf("Watchdog firing!\n");
                           watchdog_dontfire = 1;
                           if (watchdog_nmi)
                                   watchdog_ipi_nmi();
                           else
                                   kdb_enter(KDB_WHY_WATCHDOG, "mp_watchdog");
                   }
           }
           bcopy(old_pcomm, p->p_comm, MAXCOMLEN + 1);
           printf("watchdog stopped on cpu %d\n", cpuid);
   }

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