[PATCH] arm64: fix infinite stacktrace

[will.deacon@arm.com (Will Deacon)]

Hi all,

On Fri, Jun 15, 2018 at 12:58:23PM +0100, Mark Rutland wrote:
> On Thu, Jun 14, 2018 at 02:58:21PM -0400, Mikulas Patocka wrote:
> > I've got this infinite stacktrace when debugging another problem:
> > [  908.795225] INFO: rcu_preempt detected stalls on CPUs/tasks:
> > [  908.796176]  1-...!: (1 GPs behind) idle=952/1/4611686018427387904 softirq=1462/1462 fqs=355
> > [  908.797692]  2-...!: (1 GPs behind) idle=f42/1/4611686018427387904 softirq=1550/1551 fqs=355
> > [  908.799189]  (detected by 0, t=2109 jiffies, g=130, c=129, q=235)
> > [  908.800284] Task dump for CPU 1:
> > [  908.800871] kworker/1:1     R  running task        0    32      2 0x00000022
> > [  908.802127] Workqueue: writecache-writeabck writecache_writeback [dm_writecache]
> > [  908.820285] Call trace:
> > [  908.824785]  __switch_to+0x68/0x90
> > [  908.837661]  0xfffffe00603afd90
> > [  908.844119]  0xfffffe00603afd90
> > [  908.850091]  0xfffffe00603afd90
> > [  908.854285]  0xfffffe00603afd90
> > [  908.863538]  0xfffffe00603afd90
> > [  908.865523]  0xfffffe00603afd90
> > 
> > The machine just locked up and kept on printing the same line over and
> > over again. This patch fixes it.
> > 
> > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> > Cc: stable at vger.kernel.org
> 
> Given this can only occur when there's a corrupted stack (where a frame
> record points to itself), I'm not sure this requires a cc stable.
> 
> > Index: linux-2.6/arch/arm64/kernel/stacktrace.c
> > ===================================================================
> > --- linux-2.6.orig/arch/arm64/kernel/stacktrace.c
> > +++ linux-2.6/arch/arm64/kernel/stacktrace.c
> > @@ -56,6 +56,9 @@ int notrace unwind_frame(struct task_str
> >  	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
> >  	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
> >  
> > +	if (frame->fp <= fp)
> > +		return -EINVAL;
> > +
> 
> Dave Martin had a series [1] which addressed this along with a number of
> other cases where stack traces might not terminate.
> 
> Dave, do you plan to respin that?

I'd be interested in an update on that; we clearly should be fixing this in
one way or another.

Mikulus -- would you be able to test and/or review it, please?

Will