On Wed, Jul 08, 2009 at 06:40:40PM +0100, Ralf Baechle wrote:
> > The resume() implementation octeon_switch.S examines the saved
> > cp0_status register. We were clobbering the entire pt_regs structure
> > in kernel threads leading to random crashes.
> > When switching away from a kernel thread, the saved cp0_status is
> > examined and if bit 30 is set it is cleared and the CP2 state saved
> > into the pt_regs structure. Since the kernel thread stack overlaid
> > the pt_regs structure this resulted in a corrupt stack. When the
> > kthread with the corrupt stack was resumed, it could crash if it used
> > any of the data in the stack that was clobbered.
> > We fix it by moving the kernel thread stack down so it doesn't overlay
> > pt_regs.
> > Differences from v1: Don't adjust the sp by an additional 32 bytes, it
> > was not needed. Also fix up __KSTK_TOS and
> > task_pt_regs.
> Thanks for fixing and testing the issues I raised on IRC. Next I'm wonding
> what impact the uninitialized state of the stack frame we allocate may
> have. I think we're ok - but I need to stare at this for a few more