Messages in this thread | | | Date | Wed, 6 Nov 2019 14:08:38 +0100 | From | Peter Zijlstra <> | Subject | Re: NULL pointer dereference in pick_next_task_fair |
| |
On Wed, Nov 06, 2019 at 01:05:25PM +0100, Peter Zijlstra wrote: > On Mon, Oct 28, 2019 at 05:46:03PM +0000, Quentin Perret wrote: > > > > After digging a bit, the offending commit seems to be: > > > > 67692435c411 ("sched: Rework pick_next_task() slow-path") > > > > By 'offending' I mean that reverting it makes the issue go away. The > > issue comes from the fact that pick_next_entity() returns a NULL se in > > the 'simple' path of pick_next_task_fair(), which causes obvious > > problems in the subsequent call to set_next_entity(). > > > > I'll dig more, but if anybody understands the issue in the meatime feel > > free to send me a patch to try out :) > > So for all those who didn't follow along on IRC, the below seems to cure > things. > > The only thing I'm now considering is if we shouldn't be setting > ->on_cpu=2 _before_ calling put_prev_task(). I'll go audit the RT/DL > cases.
So I think it all works, but that's more by accident than anything else. I'll move the ->on_cpu=2 assignment earlier. That clearly avoids calling put_prev_task() while we're in put_prev_task().
| |