Re: LOR + panic in scope6.c

On Tuesday 09 August 2005 11:28 am, Bjoern A. Zeeb wrote:
> On Tue, 9 Aug 2005, John Baldwin wrote:
> > On Tuesday 09 August 2005 07:40 am, Bjoern A. Zeeb wrote:
> > > Hi,
> > >
> > > HEAD as of yesterday + rwatson mega-commit from today.
> > >
> > > lock order reversal
> > >  1st 0xffffff0000ad6bf0 if_afdata (if_afdata) _at_
> > > sys/netinet6/scope6.c:415 2nd 0xffffffff8081dd30 user map (user map) _at_
> > > sys/vm/vm_map.c:2997 KDB: stack backtrace:
> > >
> > > --- trap 0xc, rip = 0xffffffff804990a0, rsp = 0xffffffff809dc3f0, rbp =
> > > 0xffffffff809dc430 --- in6_setscope() at in6_setscope+0x50
> > > in6_ifdetach() at in6_ifdetach+0x24a
> > > if_detach() at if_detach+0x39
> > > ether_ifdetach() at ether_ifdetach+0x35
> > > sk_attach() at sk_attach+0x51a
> > >
> > > Fatal trap 12: page fault while in kernel mode
> > > fault virtual address   = 0x18
> > > fault code              = supervisor read, page not present
> > > instruction pointer     = 0x8:0xffffffff804990a0
> > > stack pointer           = 0x10:0xffffffff809dc3f0
> > > frame pointer           = 0x10:0xffffffff809dc430
> > > 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         = 0 (swapper)
> > > [thread pid 0 tid 0 ]
> > > Stopped at      in6_setscope+0x50:      movq    0x18(%rax),%r13
> > >
> > > (gdb) l *0xffffffff804990a0
> > > 0xffffffff804990a0 is in in6_setscope (sys/netinet6/scope6.c:417).
> > > 412             u_int32_t zoneid = 0;
> > > 413             struct scope6_id *sid;
> > > 414
> > > 415             IF_AFDATA_LOCK(ifp);
> > > 416
> > > 417             sid = SID(ifp);
> > > 418
> > > 419     #ifdef DIAGNOSTIC
> > > 420             if (sid == NULL) { /* should not happen */
> > > 421                     panic("in6_setscope: scope array is NULL");
> >
> > Well, SID is a macro that expands this to:
> >
> > 	sid = ifp->if_afdata[AF_INET6]->scope6_id
> >
> > If if_afdata[AF_INET6] has already been freed that could be the problem.
> > It might have never been non-null either I guess.  You can try having
> > in6_setscope() bail if ifp->if_afdata[AF_INET6] is NULL.
>
> I will. I think I found another problem with attach/detach in sk.
> Might be a double free.
> The above seems to happen in the "No PHY found" case (which I fixed
> already locally and everything went away).

Well, I've seen this when attach fails on de(4) as well, so I think it's some 
sort of bug where you ether_ifdetach() an interface before it's fully up or 
something.

> I will further investigate. The LOR might as well be bogus because of
> the trap.

Yes, LOR's with user map or system map after a page fault are usually bogus, 
the real problem is a trap while holding a lock.

-- 
John Baldwin <jhb_at_FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org