On Tue, Aug 01, 2017 at 06:01:56PM +0800, Yafang Shao wrote: > When we select CFQ as the scheduler, in function pick_next_task_fair
CFS, CFQ is a block IO scheduler. > it will pass NULL as the 2nd argument to pick_next_entity: > pick_next_entity(cfs_rq, NULL); > > And once __pick_first_entity() is called, it could return NULL as well. > > So in function pick_next_entity(), the local variable 'left' and 'curr' > could both be NULL, then this will cause NULL pointer issue. > > In order to fix this issue, we just need return NULL under the condition > that both 'left' and 'curr' are NULL, meaning that no entity available. And how would that happen? We only call pick_next_entity(.curr=NULL) when we _know_ cfs_rq->nr_running. > Signed-off-by: Yafang Shao <laoar.s...@gmail.com> > --- > kernel/sched/fair.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index c95880e..e64c359 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3903,6 +3903,8 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct > sched_entity *se) You diff is broken, this is very much not the clear_buddies() function. > struct sched_entity *left = __pick_first_entity(cfs_rq); > struct sched_entity *se; > > + if (!left && !curr) > + return NULL; > /* > * If curr is set we have to see if its left of the leftmost entity > * still in the tree, provided there was anything in the tree at all. > -- > 1.8.3.1 >
