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Date:      Sat, 19 Aug 2000 15:21:11 -0700 (PDT)
From:      John Polstra <jdp@polstra.com>
To:        current@freebsd.org
Subject:   Instant panic in _MEXT_ALLOC_CNT
Message-ID:  <XFMail.000819152111.jdp@polstra.com>

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With sources from this morning I am getting an instant kernel-mode
page fault in the new mbuf cluster reference counting code.  It is
failing in this statement of _MEXT_ALLOC_CNT (sys/mbuf.h), as far as
I can tell:

#define _MEXT_ALLOC_CNT(m_cnt) MBUFLOCK(                                \
        union mext_refcnt *__mcnt;                                      \
                                                                        \
        __mcnt = mext_refcnt_free;                                      \
        if ((__mcnt == NULL) && (m_alloc_ref(1) == 0))                  \
                panic("mbuf subsystem: out of ref counts!");            \
        mext_refcnt_free = __mcnt->next_ref;                            \
[*crash*]

Here is the console output and a stack trace from DDB:

Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
        The Regents of the University of California. All rights reserved.
FreeBSD 5.0-CURRENT #0: Sat Aug 19 14:49:39 PDT 2000
    jdp@blake.polstra.com:/local0/obj/local0/src/sys/BLAKE
Timecounter "i8254"  frequency 1193163 Hz
Timecounter "TSC"  frequency 400902857 Hz
CPU: Pentium II/Pentium II Xeon/Celeron (400.90-MHz 686-class CPU)
  Origin = "GenuineIntel"  Id = 0x653  Stepping = 3
 
Features=0x183f9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36
,MMX,FXSR>
real memory  = 134205440 (131060K bytes)
avail memory = 127336448 (124352K bytes)
Preloaded elf kernel "kernel" at 0xc034b000.
Pentium Pro MTRR support enabled
npx0: <math processor> on motherboard
npx0: INT 16 interface
pcib0: <Intel 82443BX (440 BX) host to PCI bridge> on motherboard
pci0: <PCI bus> on pcib0
pci0: <Intel 82443BX (440 BX) host to PCI bridge> at 0.0
pcib1: <Intel 82443BX (440 BX) PCI-PCI (AGP) bridge> at device 1.0 on pci0
pci1: <PCI bus> on pcib1
pci1: <Matrox MGA G400 AGP graphics accelerator> at 0.0 irq 11
isab0: <Intel 82371AB PCI to ISA bridge> at device 4.0 on pci0
isa0: <ISA bus> on isab0
pci0: <Intel PIIX4 ATA controller> at 4.1
pci0: <Intel 82371AB/EB (PIIX4) USB controller> at 4.2
intpm0: <Intel 82371AB Power management controller> port 0xe800-0xe80f irq 9 at
device 4.3 on pci0
intpm0: I/O mapped e800
intpm0: intr IRQ 9 enabled revision 0
smbus0: <System Management Bus> on intsmb0
smb0: <SMBus general purpose I/O> on smbus0
intpm0: PM I/O mapped e400 
ahc0: <Adaptec aic7890/91 Ultra2 SCSI adapter> port 0xd000-0xd0ff mem
0xe0000000-0xe0000fff irq 5 at device 6.0 on pci0
ahc0: aic7890/91 Wide Channel A, SCSI Id=7, 32/255 SCBs
fxp0: <Intel Pro 10/100B/100+ Ethernet> port 0xb800-0xb83f mem
0xdf000000-0xdf0fffff,0xdf800000-0xdf800fff irq 12 at device 10.
0 on pci0


Fatal trap 12: page fault while in kernel mode
fault virtual address   = 0x0
fault code              = supervisor read, page not present
instruction pointer     = 0x8:0xc02126ac
stack pointer           = 0x10:0xc035fea8
frame pointer           = 0x10:0xc035febc
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         = 0 (swapper)
interrupt mask          = net tty bio cam 
kernel: type 12 trap, code=0
Stopped at      fxp_add_rfabuf+0x170:   movl    0(%ebx),%eax
db> trace
fxp_add_rfabuf(c0a52c00,0) at fxp_add_rfabuf+0x170
fxp_attach_common(c0a52c00,c0a52cd8) at fxp_attach_common+0xb8
fxp_attach(c0a4ad80,c0a4ad80,c0a49600,c0a49580,0) at fxp_attach+0x1ad
device_probe_and_attach(c0a4ad80) at device_probe_and_attach+0x8e
bus_generic_attach(c0a49580,c0a49580,c0a49700,c0a49600,0) at bus_generic_attach+0x16
device_probe_and_attach(c0a49580) at device_probe_and_attach+0x8e
bus_generic_attach(c0a49600,c0a49600,c071b680,c0a49700,0) at bus_generic_attach+0x16
device_probe_and_attach(c0a49600) at device_probe_and_attach+0x8e
bus_generic_attach(c0a49700,c0a35080,c035ffc0,c0170c46,c0a49700) at
bus_generic_attach+0x16
nexus_attach(c0a49700,c0a49700,c02c0e10,364000,0) at nexus_attach+0xd
device_probe_and_attach(c0a49700) at device_probe_and_attach+0x8e
root_bus_configure(c071b680,c029bacc,0) at root_bus_configure+0x16
configure(0,35dc00,364000,0,c011dc09) at configure+0x33
mi_startup(0,0,0,0,0) at mi_startup+0x68
begin() at begin+0x30


John
--
  John Polstra                                               jdp@polstra.com
  John D. Polstra & Co., Inc.                        Seattle, Washington USA
  "Disappointment is a good sign of basic intelligence."  -- Chögyam Trungpa



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