/*-
 * Copyright (c) 1986, 1988, 1991, 1993
 *      The Regents of the University of California.  All rights reserved.
 * (c) UNIX System Laboratories, Inc.
 * All or some portions of this file are derived from material licensed
 * to the University of California by American Telephone and Telegraph
 * Co. or Unix System Laboratories, Inc. and are reproduced herein with
 * the permission of UNIX System Laboratories, Inc.
 *
 * 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
 *
 *      @(#)kern_shutdown.c     8.3 (Berkeley) 1/21/94
 * $FreeBSD: src/sys/kern/kern_shutdown.c,v 1.72.2.12 2002/02/21 19:15:10 dillon Exp $
 */

#include "opt_ddb.h"
#include "opt_ddb_trace.h"
#include "opt_panic.h"
#include "use_gpio.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/eventhandler.h>
#include <sys/buf.h>
#include <sys/disk.h>
#include <sys/diskslice.h>
#include <sys/reboot.h>
#include <sys/proc.h>
#include <sys/caps.h>
#include <sys/fcntl.h>          /* FREAD        */
#include <sys/stat.h>           /* S_IFCHR      */
#include <sys/vnode.h>
#include <sys/kernel.h>
#include <sys/kerneldump.h>
#include <sys/kthread.h>
#include <sys/malloc.h>
#include <sys/mount.h>
#include <sys/queue.h>
#include <sys/sysctl.h>
#include <sys/vkernel.h>
#include <sys/conf.h>
#include <sys/sysmsg.h>
#include <sys/device.h>
#include <sys/cons.h>
#include <sys/kbio.h>
#include <sys/shm.h>
#include <sys/kern_syscall.h>
#include <vm/vm_map.h>
#include <vm/pmap.h>

#include <sys/thread2.h>
#include <sys/buf2.h>
#include <sys/mplock2.h>

#include <machine/cpu.h>
#include <machine/clock.h>
#include <machine/md_var.h>
#include <machine/smp.h>                /* smp_active_mask, cpuid */
#include <machine/vmparam.h>
#include <machine/thread.h>

#include <sys/signalvar.h>

#if defined(WDOG_DISABLE_ON_PANIC)
#include <sys/wdog.h>
#endif
#include <dev/acpica/acpi_pvpanic/panic_notifier.h>
#if (NGPIO > 0) && defined(ERROR_LED_ON_PANIC)
#include <dev/misc/gpio/gpio.h>
#endif

#ifndef PANIC_REBOOT_WAIT_TIME
#define PANIC_REBOOT_WAIT_TIME 15 /* default to 15 seconds */
#endif

/*
 * Note that stdarg.h and the ANSI style va_start macro is used for both
 * ANSI and traditional C compilers.  We use the machine version to stay
 * within the confines of the kernel header files.
 */
#include <machine/stdarg.h>

#ifdef DDB
#include <ddb/ddb.h>
#ifdef DDB_UNATTENDED
int debugger_on_panic = 0;
#else
int debugger_on_panic = 1;
#endif
SYSCTL_INT(_debug, OID_AUTO, debugger_on_panic, CTLFLAG_RW,
        &debugger_on_panic, 0, "Run debugger on kernel panic");

#ifdef DDB_TRACE
int trace_on_panic = 1;
#else
int trace_on_panic = 0;
#endif
SYSCTL_INT(_debug, OID_AUTO, trace_on_panic, CTLFLAG_RW,
        &trace_on_panic, 0, "Print stack trace on kernel panic");
#endif

static int sync_on_panic = 0;
SYSCTL_INT(_kern, OID_AUTO, sync_on_panic, CTLFLAG_RW,
        &sync_on_panic, 0, "Do a sync before rebooting from a panic");

SYSCTL_NODE(_kern, OID_AUTO, shutdown, CTLFLAG_RW, 0, "Shutdown environment");

/*
 * Variable panicstr contains argument to first call to panic; used as flag
 * to indicate that the kernel has already called panic.
 */
const char *panicstr;

__read_mostly int dumping;              /* system is dumping */
static struct dumperinfo dumper;        /* selected dumper */

__read_frequently globaldata_t panic_cpu_gd;    /* used in lock assertion */
struct lwkt_tokref panic_tokens[LWKT_MAXTOKENS];
int panic_tokens_count;

__read_mostly int bootverbose = 0;      /* note: assignment to force non-bss */
SYSCTL_INT(_debug, OID_AUTO, bootverbose, CTLFLAG_RW,
           &bootverbose, 0, "Verbose kernel messages");

int cold = 1;                           /* note: assignment to force non-bss */
int dumplo;                             /* OBSOLETE - savecore compat */
u_int64_t dumplo64;

static void boot (int) __dead2;
static int setdumpdev (cdev_t dev);
static void poweroff_wait (void *, int);
static void print_uptime (void);
static void shutdown_halt (void *junk, int howto);
static void shutdown_panic (void *junk, int howto);
static void shutdown_reset (void *junk, int howto);
static int shutdown_busycount1(struct buf *bp, void *info);
static int shutdown_busycount2(struct buf *bp, void *info);
static void shutdown_cleanup_proc(struct proc *p);

/* register various local shutdown events */
static void 
shutdown_conf(void *unused)
{
        EVENTHANDLER_REGISTER(shutdown_final, poweroff_wait, NULL, SHUTDOWN_PRI_FIRST);
        EVENTHANDLER_REGISTER(shutdown_final, shutdown_halt, NULL, SHUTDOWN_PRI_LAST + 100);
        EVENTHANDLER_REGISTER(shutdown_final, shutdown_panic, NULL, SHUTDOWN_PRI_LAST + 100);
        EVENTHANDLER_REGISTER(shutdown_final, shutdown_reset, NULL, SHUTDOWN_PRI_LAST + 200);
}

SYSINIT(shutdown_conf, SI_BOOT2_MACHDEP, SI_ORDER_ANY, shutdown_conf, NULL);

/* ARGSUSED */

/*
 * The system call that results in a reboot
 *
 * MPALMOSTSAFE
 */
int
sys_reboot(struct sysmsg *sysmsg, const struct reboot_args *uap)
{
        int error;

        if ((error = caps_priv_check_self(SYSCAP_NOREBOOT | __SYSCAP_WHEELOK)))
                return (error);

        get_mplock();
        boot(uap->opt);
        rel_mplock();
        return (0);
}

/*
 * Called by events that want to shut down.. e.g  <CTL><ALT><DEL> on a PC
 */
static int shutdown_howto = 0;

void
shutdown_nice(int howto)
{
        shutdown_howto = howto;
        
        /* Send a signal to init(8) and have it shutdown the world */
        if (initproc != NULL) {
                ksignal(initproc, SIGINT);
        } else {
                /* No init(8) running, so simply reboot */
                boot(RB_NOSYNC);
        }
        return;
}
static int      waittime = -1;
struct pcb      dumppcb;
struct thread   *dumpthread;

static void
print_uptime(void)
{
        int f;
        struct timespec ts;

        getnanouptime(&ts);
        kprintf("Uptime: ");
        f = 0;
        if (ts.tv_sec >= 86400) {
                kprintf("%ldd", ts.tv_sec / 86400);
                ts.tv_sec %= 86400;
                f = 1;
        }
        if (f || ts.tv_sec >= 3600) {
                kprintf("%ldh", ts.tv_sec / 3600);
                ts.tv_sec %= 3600;
                f = 1;
        }
        if (f || ts.tv_sec >= 60) {
                kprintf("%ldm", ts.tv_sec / 60);
                ts.tv_sec %= 60;
                f = 1;
        }
        kprintf("%lds\n", ts.tv_sec);
}

/*
 *  Go through the rigmarole of shutting down..
 * this used to be in machdep.c but I'll be dammned if I could see
 * anything machine dependant in it.
 */
static void
boot(int howto)
{
        /*
         * Get rid of any user scheduler baggage and then give
         * us a high priority.
         */
        if (curthread->td_release)
                curthread->td_release(curthread);
        lwkt_setpri_self(TDPRI_MAX);

        /* collect extra flags that shutdown_nice might have set */
        howto |= shutdown_howto;

        /*
         * We really want to shutdown on the BSP.  Subsystems such as ACPI
         * can't power-down the box otherwise.
         */
        if (!CPUMASK_ISUP(smp_active_mask)) {
                kprintf("boot() called on cpu#%d\n", mycpu->gd_cpuid);
        }
        if (panicstr == NULL && mycpu->gd_cpuid != 0) {
                kprintf("Switching to cpu #0 for shutdown\n");
                lwkt_setcpu_self(globaldata_find(0));
        }
        /*
         * Do any callouts that should be done BEFORE syncing the filesystems.
         */
        EVENTHANDLER_INVOKE(shutdown_pre_sync, howto);

        /*
         * Try to get rid of any remaining FS references.  The calling
         * process, proc0, and init may still hold references.  The
         * VFS cache subsystem may still hold a root reference to root.
         *
         * XXX this needs work.  We really need to SIGSTOP all remaining
         * processes in order to avoid blowups due to proc0's filesystem
         * references going away.  For now just make sure that the init
         * process is stopped.
         */
        if (panicstr == NULL) {
                shutdown_cleanup_proc(curproc);
                shutdown_cleanup_proc(&proc0);
                if (initproc) {
                        if (initproc != curproc) {
                                ksignal(initproc, SIGSTOP);
                                tsleep(boot, 0, "shutdn", hz / 20);
                        }
                        shutdown_cleanup_proc(initproc);
                }
                vfs_cache_setroot(NULL, NULL);
        }

        /* 
         * Now sync filesystems
         */
        if (!cold && (howto & RB_NOSYNC) == 0 && waittime < 0) {
                int iter, nbusy, pbusy;
                int zcount;

                waittime = 0;
                zcount = 0;
                kprintf("\nsyncing disks... ");

                sys_sync(NULL, NULL);

                /*
                 * With soft updates, some buffers that are written will be
                 * remarked as dirty until other buffers are written.
                 *
                 * sys_sync() usually runs asynchronously, to give us a
                 * better chance of syncing the rest of the filesystems when
                 * one or more of them are stuck.
                 */
                for (iter = pbusy = 0; iter < 20 + zcount; iter++) {
                        if (iter <= 10)
                                nbusy = scan_all_buffers(shutdown_busycount1,
                                                         &iter);
                        else
                                nbusy = scan_all_buffers(shutdown_busycount2,
                                                         &iter);
                        kprintf("%d ", nbusy);
                        if (nbusy == 0) {
                                if (++zcount == 3)
                                        break;
                        } else {
                                zcount = 0;
                        }

                        /*
                         * There could be a lot to sync, only allow iter to
                         * proceed while there is progress.
                         */
                        if (nbusy < pbusy) {
                                if (iter > 10)
                                        iter = 10;
                                else
                                        iter = 0;
                        }
                        pbusy = nbusy;

                        /*
                         * XXX:
                         * Process soft update work queue if buffers don't sync
                         * after 6 iterations by permitting the syncer to run.
                         */
                        if (iter > 5)
                                bio_ops_sync(NULL);
 
                        sys_sync(NULL, NULL);
                        tsleep(boot, 0, "shutdn", hz * iter / 20 + 1);
                }
                kprintf("\n");

                if (zcount < 3) {
                        /*
                         * Failed to sync all blocks. Indicate this and don't
                         * unmount filesystems (thus forcing an fsck on reboot).
                         */
                        kprintf("giving up on %d buffers\n", nbusy);
#ifdef DDB
                        if (debugger_on_panic)
                                Debugger("busy buffer problem");
#endif /* DDB */
                        tsleep(boot, 0, "shutdn", hz * 5 + 1);
                } else {
                        kprintf("done\n");

                        /*
                         * Unmount filesystems
                         */
                        if (panicstr == NULL)
                                vfs_unmountall(1);
                }
                tsleep(boot, 0, "shutdn", hz / 10 + 1);
        }

        print_uptime();

        /*
         * Dump before doing post_sync shutdown ops
         */
        crit_enter();
        if ((howto & (RB_HALT|RB_DUMP)) == RB_DUMP && !cold) {
                dumpsys();
        }

        /*
         * Ok, now do things that assume all filesystem activity has
         * been completed.  This will also call the device shutdown
         * methods.
         */
        EVENTHANDLER_INVOKE(shutdown_post_sync, howto);

        /* Now that we're going to really halt the system... */
        EVENTHANDLER_INVOKE(shutdown_final, howto);

        for(;;) ;       /* safety against shutdown_reset not working */
        /* NOTREACHED */
}

/*
 * Pass 1 - Figure out if there are any busy or dirty buffers still present.
 *
 *      We ignore TMPFS mounts in this pass.
 */
static int
shutdown_busycount1(struct buf *bp, void *info __unused)
{
        struct vnode *vp;

        if ((vp = bp->b_vp) != NULL && vp->v_tag == VT_TMPFS)
                return (0);
        if ((bp->b_flags & B_INVAL) == 0 && BUF_LOCKINUSE(bp))
                return(1);
        if ((bp->b_flags & (B_DELWRI | B_INVAL)) == B_DELWRI)
                return (1);
        return (0);
}

/*
 * Pass 2 - only run after pass 1 has completed or has given up
 *
 *      We ignore TMPFS, NFS, MFS, and SMBFS mounts in this pass.
 */
static int
shutdown_busycount2(struct buf *bp, void *info)
{
        struct vnode *vp;
        int *iterp = info;
        const char *mpath;

        /*
         * Ignore tmpfs and nfs mounts
         */
        if ((vp = bp->b_vp) != NULL) {
                if (vp->v_tag == VT_TMPFS)
                        return (0);
                if (vp->v_tag == VT_NFS)
                        return (0);
                if (vp->v_tag == VT_MFS)
                        return (0);
                if (vp->v_tag == VT_SMBFS)
                        return (0);
        }

        /*
         * Only count buffers stuck on I/O, ignore everything else
         */
        if (((bp->b_flags & B_INVAL) == 0 && BUF_LOCKINUSE(bp)) ||
            ((bp->b_flags & (B_DELWRI|B_INVAL)) == B_DELWRI)) {
                /*
                 * Only count buffers undergoing write I/O
                 * on the related vnode.
                 */
                if (bp->b_vp == NULL || 
                    bio_track_active(&bp->b_vp->v_track_write) == 0) {
                        return (0);
                }
                if (*iterp > 15) {
                        mpath = "?";
                        if (bp->b_vp->v_mount)
                                mpath = bp->b_vp->v_mount->mnt_stat.f_mntonname;

                        kprintf("%p on %s, flags:%08x, loffset:%jd, "
                                "doffset:%jd\n",
                                bp,
                                mpath,
                                bp->b_flags,
                                (intmax_t)bp->b_loffset,
                                (intmax_t)bp->b_bio2.bio_offset);
                }
                return(1);
        }
        return(0);
}

/*
 * If the shutdown was a clean halt, behave accordingly.
 */
static void
shutdown_halt(void *junk, int howto)
{
        if (howto & RB_HALT) {
                kprintf("\n");
                kprintf("The operating system has halted.\n");
#ifdef _KERNEL_VIRTUAL
                cpu_halt();
#else
                kprintf("Please press any key to reboot.\n\n");
                cnpoll(TRUE);
                switch (cngetc()) {
                case -1:                /* No console, just die */
                        cpu_halt();
                        /* NOTREACHED */
                default:
                        howto &= ~RB_HALT;
                        break;
                }
#endif
        }
}

/*
 * Check to see if the system paniced, pause and then reboot
 * according to the specified delay.
 */
static void
shutdown_panic(void *junk, int howto)
{
        int loop;
        int c;

        if (howto & RB_DUMP) {
                if (PANIC_REBOOT_WAIT_TIME != 0) {
                        if (PANIC_REBOOT_WAIT_TIME != -1) {
                                kprintf("Automatic reboot in %d seconds - "
                                       "press a key on the console to abort\n",
                                        PANIC_REBOOT_WAIT_TIME);
                                for (loop = PANIC_REBOOT_WAIT_TIME * 10;
                                     loop > 0; --loop) {
                                        DELAY(1000 * 100); /* 1/10th second */
                                        /* Did user type a key? */
                                        c = cncheckc();
                                        if (c != -1 && c != NOKEY)
                                                break;
                                }
                                if (!loop)
                                        return;
                        }
                } else { /* zero time specified - reboot NOW */
                        return;
                }
                kprintf("--> Press a key on the console to reboot,\n");
                kprintf("--> or switch off the system now.\n");
                cngetc();
        }
}

/*
 * Everything done, now reset
 */
static void
shutdown_reset(void *junk, int howto)
{
        kprintf("Rebooting...\n");
        DELAY(1000000); /* wait 1 sec for kprintf's to complete and be read */
        /* cpu_boot(howto); */ /* doesn't do anything at the moment */
        cpu_reset();
        /* NOTREACHED */ /* assuming reset worked */
}

/*
 * Try to remove FS references in the specified process.  This function
 * is used during shutdown
 */
static
void
shutdown_cleanup_proc(struct proc *p)
{
        struct filedesc *fdp;
        struct vmspace *vm;

        if (p == NULL)
                return;
        if ((fdp = p->p_fd) != NULL) {
                kern_closefrom(0);
                if (fdp->fd_cdir) {
                        cache_drop(&fdp->fd_ncdir);
                        vrele(fdp->fd_cdir);
                        fdp->fd_cdir = NULL;
                }
                if (fdp->fd_rdir) {
                        cache_drop(&fdp->fd_nrdir);
                        vrele(fdp->fd_rdir);
                        fdp->fd_rdir = NULL;
                }
                if (fdp->fd_jdir) {
                        cache_drop(&fdp->fd_njdir);
                        vrele(fdp->fd_jdir);
                        fdp->fd_jdir = NULL;
                }
        }
        if (p->p_vkernel)
                vkernel_exit(p);
        if (p->p_textvp) {
                vrele(p->p_textvp);
                p->p_textvp = NULL;
        }
        if (p->p_textnch.ncp)
                cache_drop(&p->p_textnch);
        vm = p->p_vmspace;
        if (vm != NULL) {
                pmap_remove_pages(vmspace_pmap(vm),
                                  VM_MIN_USER_ADDRESS,
                                  VM_MAX_USER_ADDRESS);
                vm_map_remove(&vm->vm_map,
                              VM_MIN_USER_ADDRESS,
                              VM_MAX_USER_ADDRESS);
        }
}

/*
 * Magic number for savecore
 *
 * exported (symorder) and used at least by savecore(8)
 *
 * Mark it as used so that gcc doesn't optimize it away.
 */
__attribute__((__used__))
        static u_long const dumpmag = 0x8fca0101UL;

__attribute__((__used__))
        static int      dumpsize = 0;           /* also for savecore */

static int      dodump = 1;

SYSCTL_INT(_machdep, OID_AUTO, do_dump, CTLFLAG_RW, &dodump, 0,
    "Try to perform coredump on kernel panic");

void
mkdumpheader(struct kerneldumpheader *kdh, char *magic, uint32_t archver,
    uint64_t dumplen, uint32_t blksz)
{
        bzero(kdh, sizeof(*kdh));
        strncpy(kdh->magic, magic, sizeof(kdh->magic));
        strncpy(kdh->architecture, MACHINE_ARCH, sizeof(kdh->architecture));
        kdh->version = htod32(KERNELDUMPVERSION);
        kdh->architectureversion = htod32(archver);
        kdh->dumplength = htod64(dumplen);
        kdh->dumptime = htod64(time_second);
        kdh->blocksize = htod32(blksz);
        strncpy(kdh->hostname, hostname, sizeof(kdh->hostname));
        strncpy(kdh->versionstring, version, sizeof(kdh->versionstring));
        if (panicstr != NULL)
                strncpy(kdh->panicstring, panicstr, sizeof(kdh->panicstring));
        kdh->parity = kerneldump_parity(kdh);
}

static int
setdumpdev(cdev_t dev)
{
        int error;
        int doopen;

        if (dev == NULL) {
                disk_dumpconf(NULL, 0/*off*/);
                dumpdev = NULL;
                return (0);
        }

        /*
         * We have to open the device before we can perform ioctls on it,
         * or the slice/label data may not be present.  Device opens are
         * usually tracked by specfs, but the dump device can be set in
         * early boot and may not be open so this is somewhat of a hack.
         */
        doopen = (dev->si_sysref.refcnt == 1);
        if (doopen) {
                error = dev_dopen(dev, FREAD, S_IFCHR,
                                  proc0.p_ucred, NULL, NULL);
                if (error)
                        return (error);
        }
        error = disk_dumpconf(dev, 1/*on*/);
        if (error == 0)
                dumpdev = dev;

        return error;
}

/* ARGSUSED */
static void dump_conf (void *dummy);
static void
dump_conf(void *dummy)
{
        char *path;
        cdev_t dev;
        int _dummy;

        path = kmalloc(MNAMELEN, M_TEMP, M_WAITOK);
        if (TUNABLE_STR_FETCH("dumpdev", path, MNAMELEN) != 0) {
                /*
                 * Make sure all disk devices created so far have also been
                 * probed, and also make sure that the newly created device
                 * nodes for probed disks are ready, too.
                 *
                 * XXX - Delay an additional 2 seconds to help drivers which
                 *       pickup devices asynchronously and are not caught by
                 *       CAM's initial probe.
                 */
                sync_devs();
                tsleep(&_dummy, 0, "syncer", hz*2);

                dev = kgetdiskbyname(path);
                if (dev != NULL)
                        dumpdev = dev;
        }
        kfree(path, M_TEMP);
        if (setdumpdev(dumpdev) != 0)
                dumpdev = NULL;
}

SYSINIT(dump_conf, SI_SUB_DUMP_CONF, SI_ORDER_FIRST, dump_conf, NULL);

static int
sysctl_kern_dumpdev(SYSCTL_HANDLER_ARGS)
{
        int error;
        dev_t ndumpdev;

        ndumpdev = devid_from_dev(dumpdev);
        error = sysctl_handle_opaque(oidp, &ndumpdev, sizeof ndumpdev, req);
        if (error == 0 && req->newptr != NULL)
                error = setdumpdev(dev_from_devid(ndumpdev, 0));
        return (error);
}

SYSCTL_PROC(_kern, KERN_DUMPDEV, dumpdev, CTLTYPE_OPAQUE|CTLFLAG_RW,
        0, sizeof dumpdev, sysctl_kern_dumpdev, "T,udev_t", "");

static struct panicerinfo *panic_notifier;

int
set_panic_notifier(struct panicerinfo *info)
{
        if (info == NULL)
                panic_notifier = NULL;
        else if (panic_notifier != NULL)
                return 1;
        else
                panic_notifier = info;

        return 0;
}

/*
 * Panic is called on unresolvable fatal errors.  It prints "panic: mesg",
 * and then reboots.  If we are called twice, then we avoid trying to sync
 * the disks as this often leads to recursive panics.
 */
void
panic(const char *fmt, ...)
{
        int bootopt, newpanic;
        globaldata_t gd = mycpu;
        thread_t td = gd->gd_curthread;
        __va_list ap;
        static char buf[256];

        /*
         * If a panic occurs on multiple cpus before the first is able to
         * halt the other cpus, only one cpu is allowed to take the panic.
         * Attempt to be verbose about this situation but if the kprintf() 
         * itself panics don't let us overrun the kernel stack.
         *
         * Be very nasty about descheduling our thread at the lowest
         * level possible in an attempt to freeze the thread without
         * inducing further panics.
         *
         * Bumping gd_trap_nesting_level will also bypass assertions in
         * lwkt_switch() and allow us to switch away even if we are a
         * FAST interrupt or IPI.
         *
         * The setting of panic_cpu_gd also determines how kprintf()
         * spin-locks itself.  DDB can set panic_cpu_gd as well.
         */
        for (;;) {
                globaldata_t xgd = panic_cpu_gd;

                /*
                 * Someone else got the panic cpu
                 */
                if (xgd && xgd != gd) {
                        crit_enter();
                        ++mycpu->gd_trap_nesting_level;
                        if (mycpu->gd_trap_nesting_level < 25) {
                                kprintf("SECONDARY PANIC ON CPU %d THREAD %p\n",
                                        mycpu->gd_cpuid, td);
                        }
                        td->td_release = NULL;  /* be a grinch */
                        for (;;) {
                                lwkt_deschedule_self(td);
                                lwkt_switch();
                        }
                        /* NOT REACHED */
                        /* --mycpu->gd_trap_nesting_level */
                        /* crit_exit() */
                }

                /*
                 * Reentrant panic
                 */
                if (xgd && xgd == gd)
                        break;

                /*
                 * We got it
                 */
                if (atomic_cmpset_ptr(&panic_cpu_gd, NULL, gd))
                        break;
        }
        /*
         * Try to get the system into a working state.  Save information
         * we are about to destroy.
         */
        kvcreinitspin();
        if (panicstr == NULL) {
                bcopy(td->td_toks_array, panic_tokens, sizeof(panic_tokens));
                panic_tokens_count = td->td_toks_stop - &td->td_toks_base;
        }
        lwkt_relalltokens(td);
        td->td_toks_stop = &td->td_toks_base;
        if (gd->gd_spinlocks)
                kprintf("panic with %d spinlocks held\n", gd->gd_spinlocks);
        gd->gd_spinlocks = 0;

        /*
         * Setup
         */
        bootopt = RB_AUTOBOOT | RB_DUMP;
        if (sync_on_panic == 0)
                bootopt |= RB_NOSYNC;
        newpanic = 0;
        if (panicstr) {
                bootopt |= RB_NOSYNC;
        } else {
                panicstr = fmt;
                newpanic = 1;
        }

        /*
         * Format the panic string.
         */
        __va_start(ap, fmt);
        kvsnprintf(buf, sizeof(buf), fmt, ap);
        if (panicstr == fmt)
                panicstr = buf;
        __va_end(ap);
        if (panic_notifier != NULL)
                panic_notifier->notifier(panic_notifier->arg);
        kprintf("panic: %s\n", buf);
        /* two separate prints in case of an unmapped page and trap */
        kprintf("cpuid = %d\n", mycpu->gd_cpuid);

#if (NGPIO > 0) && defined(ERROR_LED_ON_PANIC)
        led_switch("error", 1);
#endif

#if defined(WDOG_DISABLE_ON_PANIC)
        wdog_disable();
#endif

        /*
         * Make sure kgdb knows who we are, there won't be a stoppcbs[]
         * entry since our cpu wasn't stopped.
         */
        savectx(&dumppcb);
        dumpthread = curthread;

        /*
         * Enter the debugger or fall through & dump.  Entering the
         * debugger will stop cpus.  If not entering the debugger stop
         * cpus here.
         *
         * Limit the trace history to leave more panic data on a
         * potentially row-limited console.
         */

#if defined(DDB)
        if (newpanic && trace_on_panic)
                print_backtrace(6);
        if (debugger_on_panic)
                Debugger("panic");
        else
#endif
        if (newpanic)
                stop_cpus(mycpu->gd_other_cpus);
        boot(bootopt);
}

/*
 * Support for poweroff delay.
 */
#ifndef POWEROFF_DELAY
# define POWEROFF_DELAY 5000
#endif
static int poweroff_delay = POWEROFF_DELAY;

SYSCTL_INT(_kern_shutdown, OID_AUTO, poweroff_delay, CTLFLAG_RW,
        &poweroff_delay, 0, "");

static void 
poweroff_wait(void *junk, int howto)
{
        if(!(howto & RB_POWEROFF) || poweroff_delay <= 0)
                return;
        DELAY(poweroff_delay * 1000);
}

/*
 * Some system processes (e.g. syncer) need to be stopped at appropriate
 * points in their main loops prior to a system shutdown, so that they
 * won't interfere with the shutdown process (e.g. by holding a disk buf
 * to cause sync to fail).  For each of these system processes, register
 * shutdown_kproc() as a handler for one of shutdown events.
 */
static int kproc_shutdown_wait = 60;
SYSCTL_INT(_kern_shutdown, OID_AUTO, kproc_shutdown_wait, CTLFLAG_RW,
    &kproc_shutdown_wait, 0, "");

void
shutdown_kproc(void *arg, int howto)
{
        struct thread *td;
        struct proc *p;
        int error;

        if (panicstr)
                return;

        td = (struct thread *)arg;
        if ((p = td->td_proc) != NULL) {
            kprintf("Waiting (max %d seconds) for system process `%s' to stop...",
                kproc_shutdown_wait, p->p_comm);
        } else {
            kprintf("Waiting (max %d seconds) for system thread %s to stop...",
                kproc_shutdown_wait, td->td_comm);
        }
        error = suspend_kproc(td, kproc_shutdown_wait * hz);

        if (error == EWOULDBLOCK)
                kprintf("timed out\n");
        else
                kprintf("stopped\n");
}

/* Registration of dumpers */
int
set_dumper(struct dumperinfo *di)
{
        if (di == NULL) {
                bzero(&dumper, sizeof(dumper));
                return 0;
        }

        if (dumper.dumper != NULL)
                return (EBUSY);

        dumper = *di;
        return 0;
}

void
dumpsys(void)
{
#if defined (_KERNEL_VIRTUAL)
        /* vkernels don't support dumps */
        kprintf("vkernels don't support dumps\n");
        return;
#endif
        /*
         * If there is a dumper registered and we aren't dumping already, call
         * the machine dependent dumpsys (md_dumpsys) to do the hard work.
         *
         * XXX: while right now the md_dumpsys() of x86 and x86_64 could be
         *      factored out completely into here, I rather keep them machine
         *      dependent in case we ever add a platform which does not share
         *      the same dumpsys() code, such as arm.
         */
        if (dumper.dumper != NULL && !dumping) {
                dumping++;
                md_dumpsys(&dumper);
        }
}

__read_frequently int dump_stop_usertds = 0;

static
void
need_user_resched_remote(void *dummy)
{
        need_user_resched();
}

void
dump_reactivate_cpus(void)
{
        globaldata_t gd;
        int cpu, seq;

        dump_stop_usertds = 1;

        need_user_resched();

        for (cpu = 0; cpu < ncpus; cpu++) {
                gd = globaldata_find(cpu);
                seq = lwkt_send_ipiq(gd, need_user_resched_remote, NULL);
                lwkt_wait_ipiq(gd, seq);
        }

        restart_cpus(stopped_cpus);
}