Re: panic in pmap_remove_pages()

On Fri, Jan 23, 2015 at 12:51:00PM +0200, Konstantin Belousov wrote:
> On Wed, Jan 21, 2015 at 01:47:06PM -0800, Steve Kargl wrote:
> > Fatal trap 9: general protection fault while in kernel mode
> > cpuid = 3; apic id = 13
> > instruction pointer     = 0x20:0xffffffff8079abf9
> > stack pointer           = 0x28:0xfffffe047325e360
> > frame pointer           = 0x28:0xfffffe047325e440
> > code segment            = base 0x0, limit 0xfffff, type 0x1b
> >                         = DPL 0, pres 1, long 1, def32 0, gran 1
> > processor eflags        = interrupt enabled, resume, IOPL = 0
> > current process         = 41779 (z)
> > trap number             = 9
> > panic: general protection fault
> > cpuid = 3
> > KDB: stack backtrace:
> > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xfffffe047325e020
> > panic() at panic+0x1c1/frame 0xfffffe047325e0e0
> > trap_fatal() at trap_fatal+0x396/frame 0xfffffe047325e140
> > trap() at trap+0x6ce/frame 0xfffffe047325e2a0
> > calltrap() at calltrap+0x8/frame 0xfffffe047325e2a0
> > --- trap 0x9, rip = 0xffffffff8079abf9, rsp = 0xfffffe047325e360, rbp = 0xfffffe047325e440 ---
> > pmap_remove_pages() at pmap_remove_pages+0x539/frame 0xfffffe047325e440
> > exec_new_vmspace() at exec_new_vmspace+0x180/frame 0xfffffe047325e4a0
> > exec_elf64_imgact() at exec_elf64_imgact+0x6c0/frame 0xfffffe047325e570
> > kern_execve() at kern_execve+0x484/frame 0xfffffe047325e8c0
> > sys_execve() at sys_execve+0x35/frame 0xfffffe047325e920
> > amd64_syscall() at amd64_syscall+0x289/frame 0xfffffe047325ea30
> > Xfast_syscall() at Xfast_syscall+0xfb/frame 0xfffffe047325ea30
> > --- syscall (59, FreeBSD ELF64, sys_execve), rip = 0x4251ba, rsp = 0x7ffffe8ebab8, rbp = 0x7ffffe8ec1c0 ---
> > Uptime: 22d22h22m46s
> > 
> > #0  doadump (textdump=1) at pcpu.h:219
> > 219	pcpu.h: No such file or directory.
> > 	in pcpu.h
> > (kgdb) #0  doadump (textdump=1) at pcpu.h:219
> > #1  0xffffffff80555bd7 in kern_reboot (howto=260)
> >     at /usr/src/sys/kern/kern_shutdown.c:447
> > #2  0xffffffff80556040 in panic (fmt=<value optimized out>)
> >     at /usr/src/sys/kern/kern_shutdown.c:746
> > #3  0xffffffff807a2986 in trap_fatal (frame=<value optimized out>, 
> >     eva=<value optimized out>) at /usr/src/sys/amd64/amd64/trap.c:867
> > #4  0xffffffff807a25de in trap (frame=<value optimized out>)
> >     at /usr/src/sys/amd64/amd64/trap.c:201
> > #5  0xffffffff80787ca3 in calltrap ()
> >     at /usr/src/sys/amd64/amd64/exception.S:235
> > #6  0xffffffff8079abf9 in pmap_remove_pages (pmap=0xfffff801c627dec8)
> >     at /usr/src/sys/amd64/amd64/pmap.c:5389
> Please do 'frame 6' and from there, do 'p *m'.  Is it reproducable ?
> 

(kgdb) p *m
$9 = {plinks = {q = {tqe_next = 0xfffff804384044c0, 
      tqe_prev = 0xfffff8042e89eac0}, s = {ss = {
        sle_next = 0xfffff804384044c0}, pv = 0xfffff8042e89eac0}, memguard = {
      p = 18446735295740134592, v = 18446735295577189056}}, listq = {
    tqe_next = 0xfffff8043cddb158, tqe_prev = 0xfffff804335c2358}, 
  object = 0xfffff801882d5100, pindex = 30, phys_addr = 4352778240, md = {
    pv_list = {tqh_first = 0xfffff800bc1d37a8, tqh_last = 0xfefff800bc1d37b0}, 
    pv_gen = 1012, pat_mode = 6}, wire_count = 0, busy_lock = 1, 
  hold_count = 0, flags = 0, aflags = 1 '\001', oflags = 0 '\0', 
  queue = 1 '\001', psind = 0 '\0', segind = 7 '\a', order = 13 '\r', 
  pool = 0 '\0', act_count = 5 '\005', valid = 255 'ÿ', dirty = 255 'ÿ'}

It would have been reproducible except that the panic truncated
the program 'z' (which caused the panic) to 0 bytes and took the
source code I was writing.  Neither 'z' nor the source code appeared
in /usr/lost+found.  Unfortunately, the source code was a quickly
written Fortran program with obviously a programming error, and I
doubt that I'll be able to replicate the program.

-- 
Steve