The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/amd64/amd64/mp_watchdog.c

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    1 /*-
    2  * Copyright (c) 2004 Robert N. M. Watson
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  *
   26  * $FreeBSD: releng/9.1/sys/amd64/amd64/mp_watchdog.c 214631 2010-11-01 18:18:46Z jhb $
   27  */
   28 
   29 #include "opt_mp_watchdog.h"
   30 #include "opt_sched.h"
   31 
   32 #ifdef SCHED_ULE
   33 #error MP_WATCHDOG cannot currently be used with SCHED_ULE
   34 #endif
   35 
   36 #include <sys/param.h>
   37 #include <sys/kdb.h>
   38 #include <sys/kernel.h>
   39 #include <sys/lock.h>
   40 #include <sys/mutex.h>
   41 #include <sys/pcpu.h>
   42 #include <sys/proc.h>
   43 #include <sys/sysctl.h>
   44 #include <sys/systm.h>
   45 
   46 #include <machine/smp.h>
   47 #include <x86/apicreg.h>
   48 #include <machine/apicvar.h>
   49 #include <machine/mp_watchdog.h>
   50 
   51 /*
   52  * mp_watchdog hijacks the idle thread on a specified CPU, prevents new work
   53  * from being scheduled there, and uses it as a "watchdog" to detect kernel
   54  * failure on other CPUs.  This is made reasonable by inclusion of logical
   55  * processors in Xeon hardware.  The watchdog is configured by setting the
   56  * debug.watchdog sysctl/tunable to the CPU of interest.  A callout will then
   57  * begin executing reseting a timer that is gradually lowered by the watching
   58  * thread.  If the timer reaches 0, the watchdog fires by ether dropping
   59  * directly to the debugger, or by sending an NMI IPI to the boot processor.
   60  * This is a somewhat less efficient substitute for dedicated watchdog
   61  * hardware, but can be quite an effective tool for debugging hangs.
   62  *
   63  * XXXRW: This should really use the watchdog(9)/watchdog(4) framework, but
   64  * doesn't yet.
   65  */
   66 static int      watchdog_cpu = -1;
   67 static int      watchdog_dontfire = 1;
   68 static int      watchdog_timer = -1;
   69 static int      watchdog_nmi = 1;
   70 
   71 TUNABLE_INT("debug.watchdog", &watchdog_cpu);
   72 SYSCTL_INT(_debug, OID_AUTO, watchdog_nmi, CTLFLAG_RW, &watchdog_nmi, 0,
   73     "IPI the boot processor with an NMI to enter the debugger");
   74 
   75 static struct callout   watchdog_callout;
   76 
   77 static void watchdog_change(int wdcpu);
   78 
   79 /*
   80  * Number of seconds before the watchdog will fire if the callout fails to
   81  * reset the timer.
   82  */
   83 #define WATCHDOG_THRESHOLD      10
   84 
   85 static void
   86 watchdog_init(void *arg)
   87 {
   88 
   89         callout_init(&watchdog_callout, CALLOUT_MPSAFE);
   90         if (watchdog_cpu != -1)
   91                 watchdog_change(watchdog_cpu);
   92 }
   93 
   94 /*
   95  * This callout resets a timer until the watchdog kicks in.  It acquires some
   96  * critical locks to make sure things haven't gotten wedged with hose locks
   97  * held.
   98  */
   99 static void
  100 watchdog_function(void *arg)
  101 {
  102 
  103         /*
  104          * Since the timer ran, we must not be wedged.  Acquire some critical
  105          * locks to make sure.  Then reset the timer.
  106          */
  107         mtx_lock(&Giant);
  108         watchdog_timer = WATCHDOG_THRESHOLD;
  109         mtx_unlock(&Giant);
  110         callout_reset(&watchdog_callout, 1 * hz, watchdog_function, NULL);
  111 }
  112 SYSINIT(watchdog_init, SI_SUB_DRIVERS, SI_ORDER_ANY, watchdog_init, NULL);
  113 
  114 static void
  115 watchdog_change(int wdcpu)
  116 {
  117 
  118         if (wdcpu == -1 || wdcpu == 0xffffffff) {
  119                 /*
  120                  * Disable the watchdog.
  121                  */
  122                 watchdog_cpu = -1;
  123                 watchdog_dontfire = 1;
  124                 callout_stop(&watchdog_callout);
  125                 printf("watchdog stopped\n");
  126         } else {
  127                 watchdog_timer = WATCHDOG_THRESHOLD;
  128                 watchdog_dontfire = 0;
  129                 watchdog_cpu = wdcpu;
  130                 callout_reset(&watchdog_callout, 1 * hz, watchdog_function,
  131                     NULL);
  132         }
  133 }
  134 
  135 /*
  136  * This sysctl sets which CPU is the watchdog CPU.  Set to -1 or 0xffffffff
  137  * to disable the watchdog.
  138  */
  139 static int
  140 sysctl_watchdog(SYSCTL_HANDLER_ARGS)
  141 {
  142         int error, temp;
  143 
  144         temp = watchdog_cpu;
  145         error = sysctl_handle_int(oidp, &temp, 0, req);
  146         if (error)
  147                 return (error);
  148 
  149         if (req->newptr != NULL)
  150                 watchdog_change(temp);
  151         return (0);
  152 }
  153 SYSCTL_PROC(_debug, OID_AUTO, watchdog, CTLTYPE_INT|CTLFLAG_RW, 0, 0,
  154     sysctl_watchdog, "I", "");
  155 
  156 /*
  157  * Drop into the debugger by sending an IPI NMI to the boot processor.
  158  */
  159 static void
  160 watchdog_ipi_nmi(void)
  161 {
  162 
  163         /*
  164          * Deliver NMI to the boot processor.  Why not?
  165          */
  166         lapic_ipi_raw(APIC_DEST_DESTFLD | APIC_TRIGMOD_EDGE |
  167             APIC_LEVEL_ASSERT | APIC_DESTMODE_PHY | APIC_DELMODE_NMI,
  168             boot_cpu_id);
  169         lapic_ipi_wait(-1);
  170 }
  171 
  172 /*
  173  * ap_watchdog() is called by the SMP idle loop code.  It works on the same
  174  * premise that the disabling of logical processors does: that if the cpu is
  175  * idle, then it can ignore the world from then on, as nothing will be
  176  * scheduled on it.  Leaving aside multi-runqueue schedulers (SCHED_ULE) and
  177  * explicit process migration (sched_bind()), this is not an unreasonable
  178  * assumption.
  179  */
  180 void
  181 ap_watchdog(u_int cpuid)
  182 {
  183         char old_pcomm[MAXCOMLEN + 1];
  184         struct proc *p;
  185 
  186         if (watchdog_cpu != cpuid)
  187                 return;
  188 
  189         printf("watchdog started on cpu %d\n", cpuid);
  190         p = curproc;
  191         bcopy(p->p_comm, old_pcomm, MAXCOMLEN + 1);
  192         snprintf(p->p_comm, MAXCOMLEN + 1, "mp_watchdog cpu %d", cpuid);
  193         while (1) {
  194                 DELAY(1000000);                         /* One second. */
  195                 if (watchdog_cpu != cpuid)
  196                         break;
  197                 atomic_subtract_int(&watchdog_timer, 1);
  198                 if (watchdog_timer < 4)
  199                         printf("Watchdog timer: %d\n", watchdog_timer);
  200                 if (watchdog_timer == 0 && watchdog_dontfire == 0) {
  201                         printf("Watchdog firing!\n");
  202                         watchdog_dontfire = 1;
  203                         if (watchdog_nmi)
  204                                 watchdog_ipi_nmi();
  205                         else
  206                                 kdb_enter(KDB_WHY_WATCHDOG, "mp_watchdog");
  207                 }
  208         }
  209         bcopy(old_pcomm, p->p_comm, MAXCOMLEN + 1);
  210         printf("watchdog stopped on cpu %d\n", cpuid);
  211 }

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