lkml.org 
[lkml]   [2019]   [Dec]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: Crash in fair scheduler
On Tue, Dec 03, 2019 at 09:11:14AM +0000, Schmid, Carsten wrote:
> Hi maintainers of the fair scheduler,
>
> we had a crash in the fair scheduler and analysis shows that this could happen again.
> Happened on 4.14.86 (LTS series) but failing code path still exists in 5.4-rc2 (and 4.14.147 too).

Please, do try if you can reproduce with Linus' latest git. I've no idea
what is, or is not, in those stable trees.

> crash> * cfs_rq ffff99a96dda9800
> struct cfs_rq {
> load = { weight = 1048576, inv_weight = 0 },
> nr_running = 1,
> h_nr_running = 1,
> exec_clock = 0,
> min_vruntime = 190894920101,
> tasks_timeline = { rb_root = { rb_node = 0xffff99a9502e0d10 }, rb_leftmost = 0x0 },
> curr = 0x0,
> next = 0x0,
> last = 0x0,
> skip = 0x0,


> &cfs_rq->tasks_timeline->rb_leftmost
> tasks_timeline = {
> rb_root = {
> rb_node = 0xffff99a9502e0d10
> },
> rb_leftmost = 0x0
> },

> include/linux/rbtree.h:91:#define rb_first_cached(root) (root)->rb_leftmost

> struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
> {
> struct rb_node *left = rb_first_cached(&cfs_rq->tasks_timeline);
>
> if (!left)
> return NULL; <<<<<<<<<< the case
>
> return rb_entry(left, struct sched_entity, run_node);
> }

This the problem, for some reason the rbtree code got that rb_leftmost
thing wrecked.

> Is this a corner case nobody thought of or do we have cfs_rq data that is unexpected in it's content?

No, the rbtree is corrupt. Your tree has a single node (which matches
with nr_running), but for some reason it thinks rb_leftmost is NULL.
This is wrong, if the tree is non-empty, it must have a leftmost
element.

Can you reproduce at will? If so, can you please try the latest kernel,
and or share the reproducer?

\
 
 \ /
  Last update: 2019-12-03 11:31    [W:0.053 / U:0.536 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site