[Bug 233511] [panic] Fatal trap 12: page fault while in kernel mode (kern_ptrace, sys_process.c:1148)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=233511

            Bug ID: 233511
           Summary: [panic] Fatal trap 12: page fault while in kernel mode
                    (kern_ptrace, sys_process.c:1148)
           Product: Base System
           Version: 11.2-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: nicholas.h.briggs at gmail.com

using "truss", tracing a process that might have been stopped

Fatal trap 12: page fault while in kernel mode
cpuid = 0; apic id = 00
fault virtual address   = 0x1d0
fault code              = supervisor write, page not present
instruction pointer     = 0x20:0xc0becb50
stack pointer           = 0x28:0xd6563a68
frame pointer           = 0x28:0xd6563b1c
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, def32 1, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 80728 (truss)
trap number             = 12
panic: page fault
cpuid = 0
KDB: stack backtrace:
#0 0xc0bcd3be at kdb_backtrace+0x4e
#1 0xc0b8ca08 at vpanic+0x108
#2 0xc0b8c8f4 at panic+0x14
#3 0xc109fc3e at trap_fatal+0x32e
#4 0xc109fc83 at trap_pfault+0x33
#5 0xc109f3e2 at trap+0x332
#6 0xc108d6c7 at calltrap+0x6
#7 0xc0bebae0 at sys_ptrace+0xd0
#8 0xc10a0a69 at syscall+0xa29
#9 0xc108d77b at Xint0x80_syscall+0x2b


(kgdb)
#0  0xc0b8c8a5 in doadump (textdump=<value optimized out>)
    at /usr/src/sys/kern/kern_shutdown.c:314
#1  0xc0b8c6f3 in kern_reboot (howto=260)
    at /usr/src/sys/kern/kern_shutdown.c:383
#2  0xc0b8ca3c in vpanic (fmt=0xc11c0d6e "%s", ap=0xd656390c "<C6><E9>f<C1>")
    at /usr/src/sys/kern/kern_shutdown.c:776
#3  0xc0b8c8f4 in panic (fmt=0xc11c0d6e "%s")
    at /usr/src/sys/kern/kern_shutdown.c:707
#4  0xc109fc3e in trap_fatal (frame=<value optimized out>, 
    eva=<value optimized out>) at /usr/src/sys/i386/i386/trap.c:992
#5  0xc109fc83 in trap_pfault (frame=<value optimized out>, usermode=0, 
    eva=464) at pcpu.h:226
#6  0xc109f3e2 in trap (frame=0xd6563a28) at /usr/src/sys/i386/i386/trap.c:508
#7  0xc108d6c7 in calltrap () at /usr/src/sys/i386/i386/exception.s:172
#8  0xc0becb50 in kern_ptrace (td=0xc4907800, req=10, pid=80660, addr=0x0, 
    data=-1052223757) at /usr/src/sys/kern/sys_process.c:1146
#9  0xc0bebae0 in sys_ptrace (td=0xc4907800, uap=0xc4907b68)
    at /usr/src/sys/kern/sys_process.c:627
#10 0xc10a0a69 in syscall (frame=0xd6563ce8) at subr_syscall.c:132
#11 0xc108d77b in Xint0x80_syscall ()
    at /usr/src/sys/i386/i386/exception.s:286


(kgdb) list *0xc0becb50
0xc0becb50 is in kern_ptrace (/usr/src/sys/kern/sys_process.c:1148).
1143                    }
1144                    p->p_xsig = data;
1145                    p->p_xthread = NULL;
1146                    if ((p->p_flag & (P_STOPPED_SIG | P_STOPPED_TRACE)) !=
0) {
1147                            /* deliver or queue signal */
1148                            td2->td_dbgflags &= ~TDB_XSIG;
1149                            td2->td_xsig = data;
1150    
1151                            /*
1152                             * P_WKILLED is insurance that a
PT_KILL/SIGKILL always

at this point, td2 is 0x0.  "p" is unavailable, "<value optimized out>"

I will keep the core file in case there's anything else that would be useful.

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