Messages in this thread Patch in this message | | | Date | Tue, 29 Oct 2019 12:34:11 +0100 | From | Peter Zijlstra <> | Subject | Re: NULL pointer dereference in pick_next_task_fair |
| |
On Mon, Oct 28, 2019 at 05:46:03PM +0000, Quentin Perret wrote: > The issue is very transient and relatively hard to reproduce. > > 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 :)
Can you please see if this makes any difference?
--- kernel/sched/core.c | 6 ++++-- kernel/sched/fair.c | 2 +- kernel/sched/idle.c | 3 +-- 3 files changed, 6 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 7880f4f64d0e..abd2d4f80381 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3922,8 +3922,10 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) goto restart;
/* Assumes fair_sched_class->next == idle_sched_class */ - if (unlikely(!p)) - p = idle_sched_class.pick_next_task(rq, prev, rf); + if (unlikely(!p)) { + prev->sched_class->put_prev_task(rq, prev, rf); + p = idle_sched_class.pick_next_task(rq, NULL, NULL); + }
return p; } diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 83ab35e2374f..2aad94bb7165 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6820,7 +6820,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf simple: #endif if (prev) - put_prev_task(rq, prev); + prev->sched_class->put_prev_task(rq, prev, rf);
do { se = pick_next_entity(cfs_rq, NULL); diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 8dad5aa600ea..e8dfc84f375a 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -390,8 +390,7 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf { struct task_struct *next = rq->idle;
- if (prev) - put_prev_task(rq, prev); + WARN_ON_ONCE(prev || rf);
set_next_task_idle(rq, next);
| |