ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

[Benjamin Herrenschmidt]

> > Oops: Exception in kernel mode, sig: 11 [#1]
> > Exsw1600
> > Modules linked in:
> > NIP: c00bbb20 LR: c00bbb20 CTR: 00000000
> > REGS: dd5b1c50 TRAP: 0700   Not tainted  (2.6.27-rc2)
> > MSR: 00029000 <EE,ME>  CR: 24082282  XER: 20000000
> > TASK = ddcce060[1707] 'find' THREAD: dd5b0000
> > GPR00: 00000000 dd5b1d00 ddcce060 dd801180 dd5b1d68 dd5b1d58 dd80125b 
> > 100234ec
> > GPR08: c0800000 00019330 0000ffff dd5b1d20 24000288 100ad874 100936f8 
> > 1008a1d0
> > GPR16: 10083f80 dd5b1e2c dd5b1d68 fffffff4 c0380000 dd5b1d60 dd5b1d58 
> > dd802084
> > GPR24: dc3d7700 dd802018 dd5b1d68 c0380000 dd801180 dd5b1d68 00000000 
> > dd5b1d00
> > NIP [c00bbb20] d_lookup+0x40/0x90
> > LR [c00bbb20] d_lookup+0x40/0x90
> > Call Trace:
> > [dd5b1d00] [dd5b1d58] 0xdd5b1d58 (unreliable)
> 
> Can you check if, at some point during the system execution (starting
> from boot), 0xdd5b1d58 is an address where a module is loaded ? (the
> module can be later unloaded, what I wonder is if this address would
> appear to have had a loaded+unloaded module).
> 
> Actually, could you try to compile your kernel without "MODULE_UNLOAD" ?

I've had similar crashes (with similar backtraces in the VFS) on
machines with no modules, netbooted zImages.

Ben.