Re: Fatal trap 1 [Was: "Memory modified after free" - by whom?]

On Sat, Dec 22, 2012 at 01:08:10PM +0200, Andriy Gapon wrote:
> on 22/12/2012 02:21 Garrett Cooper said the following:
> > Fatal trap 1: privileged instruction fault while in kernel mode
> > Fatal trap 1: privileged instruction fault while in kernel mode
> 
> Unrelated to the original topic - this looks very weird.
> I mean all the CPUs getting this unusual trap...
> Could you please do 'disassemble 0xffffffff80af5099' in kgdb with the same
> kernel.  Or if you have a different kernel now, please use "instruction pointer"
> value from a trap with that kernel.
> 
This is due to the vtoslab() returning NULL. Since slabref is
dereferenced later, clang tries to be helpful as usual and converts
the !(p->flags & PG_SLAB) case from vtoslab() into the jump to un2
instruction if vtoslab() result is NULL.

So instead of KASSERT triggering the next line, you see this improvement.

> > Memory modified after free 0xffffff800040d000(9216) val=5a5a5a5a _at_
> > 0xffffff800040d000
> > Fatal trap 1: privileged instruction fault while in kernel mode
> > cpuid = 3;
> > cpuid = 1;
> > apic id = 02
> > cpuid = 0; apic id = 06
> > apic id = 00
> > instruction pointer     = 0x20:0xffffffff80af5099
> > instruction pointer     = 0x20:0xffffffff80af5099
> > instruction pointer     = 0x20:0xffffffff80af5099
> > Fatal trap 1: privileged instruction fault while in kernel mode
> > stack pointer           = 0x28:0xffffff8496fff880
> > stack pointer           = 0x28:0xffffff8496fe1880
> > cpuid = 2; frame pointer                = 0x28:0xffffff8496fff8b0
> > frame pointer           = 0x28:0xffffff8496fe18b0
> > stack pointer           = 0x28:0xffffff849705d880
> > code segment            = base 0x0, limit 0xfffff, type 0x1b
> > frame pointer           = 0x28:0xffffff849705d8b0
> > apic id = 04
> > code segment            = base 0x0, limit 0xfffff, type 0x1b
> > code segment            = base 0x0, limit 0xfffff, type 0x1b
> >                         = DPL 0, pres 1, long 1, def32 0, gran 1
> >                         = DPL 0, pres 1, long 1, def32 0, gran 1
> > instruction pointer     = 0x20:0xffffffff80af5099
> > processor eflags        =                       = DPL 0, pres 1, long
> > 1, def32 0, gran 1
> > interrupt enabled, processor eflags     = stack pointer         =
> > 0x28:0xffffff8497067880
> > interrupt enabled, resume, resume, frame pointer                =
> > 0x28:0xffffff84970678b0
> > IOPL = 0
> > code segment            = base 0x0, limit 0xfffff, type 0x1b
> > current process         =                       = DPL 0, pres 1, long
> > 1, def32 0, gran 1
> > processor eflags        = 12 (irq280: ix0:que 3)
> > ilock order reversal: (Giant after non-sleepable)
> >  1st 0xfffffe0078148b38 ix0:rx(3) (ix0:rx(3)) _at_
> > /usr/src/sys/modules/ixgbe/../../dev/ixgbe/ixgbe.c:4296
> >  2nd 0xffffffff814457b8 Giant (Giant) _at_ /usr/src/sys/dev/usb/input/ukbd.c:1946
> > KDB: stack backtrace:
> > db_trace_self_wrapper() at db_trace_self_wrapper+0x2b/frame 0xffffff8496fff320
> > kdb_backtrace() at kdb_backtrace+0x39/frame 0xffffff8496fff3d0
> > witness_checkorder() at witness_checkorder+0xc47/frame 0xffffff8496fff450
> > __mtx_lock_flags() at __mtx_lock_flags+0x89/frame 0xffffff8496fff490
> > ukbd_poll() at ukbd_poll+0x28/frame 0xffffff8496fff4b0
> > kbdmux_poll() at kbdmux_poll+0x5b/frame 0xffffff8496fff4d0
> > cngrab() at cngrab+0x35/frame 0xffffff8496fff4f0
> > kdb_trap() at kdb_trap+0x124/frame 0xffffff8496fff550
> > trap_fatal() at trap_fatal+0x345/frame 0xffffff8496fff5b0
> > trap() at trap+0x836/frame 0xffffff8496fff7c0
> > calltrap() at calltrap+0x8/frame 0xffffff8496fff7c0
> > --- trap 0x1, rip = 0xffffffff80af5099, rsp = 0xffffff8496fff880, rbp
> > = 0xffffff8496fff8b0 ---
> > uma_find_refcnt() at uma_find_refcnt+0x79/frame 0xffffff8496fff8b0
> 
> 
> -- 
> Andriy Gapon
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