On Sat, Oct 21, 2017 at 04:06:52PM +0200, Thomas Gleixner wrote:
> The recent rework of the cpu hotplug internals changed the usage of the per
> cpu state->node field, but missed to clean it up after usage.
>
> So subsequent hotplug operations use the stale pointer from a previous
> operation and hand it into the callback functions. The callbacks then
> dereference a pointer which either belongs to a different facility or
> points to freed and potentially reused memory. In either case data
> corruption and crashes are the obvious consequence.
>
> Reset the node and the last pointers in the per cpu state to NULL after the
> operation which set them has completed.
>
> Fixes: 96abb968549c ("smp/hotplug: Allow external multi-instance rollback")
> Reported-by: Tvrtko Ursulin <tursu...@ursulin.net>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
This does fine with rcutorture, though it does not fix the lost
(or egregiously delayed) timer problem that is still eluding me.
Nevertheless, for whatever it is worth:
Tested-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> ---
> kernel/cpu.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -632,6 +632,11 @@ cpuhp_invoke_ap_callback(int cpu, enum c
> __cpuhp_kick_ap(st);
> }
>
> + /*
> + * Clean up the leftovers so the next hotplug operation wont use stale
> + * data.
> + */
> + st->node = st->last = NULL;
> return ret;
> }
>
>
