Re: [patch] Re: [PowerPC][Linux-next][6.11.0-rc4-next-20240820] OOPs while running LTP FS Stress

From: Venkat Rao Bagalkote
Date: Thu Sep 19 2024 - 10:39:59 EST


Hello Mike,

Thanks for the patch. I applied your patch and verified the issue, and can confirm your patch fixes the issue.


Please add the below tags.


Reported-by: Venkat Rao Bagalkote <venkat88@xxxxxxxxxxxxxxxxxx>

Tested-by: Venkat Rao Bagalkote <venkat88@xxxxxxxxxxxxxxxxxx>


Regards,

Venkat.

On 19/09/24 11:39 am, Mike Galbraith wrote:
On Mon, 2024-09-16 at 12:00 +0530, Venkat Rao Bagalkote wrote:
Greetings!!!
Greetings,

I am seeing below kernel crash from 6.11.0-rc4-next-20240820.


Tried to do git bisect, but it didnt point to right patch. Attached is
the bisect log.

Any help in fixing this is much appriciated.
I met this, as well as other ways the wheels can fall off that turned
out to have the same root. I gave Peter a heads up with diag offline,
but having now convinced myself that all is well, I'll go ahead and
post a patchlet.

At the very least it's worth putting out for wider testing.. and should
anyone have something prettier in mind, yeah, do that instead.

sched: Fix sched_delayed vs cfs_bandwidth

Meeting an unfinished DELAY_DEQUEUE treated entity in unthrottle_cfs_rq()
leads to a couple terminal scenarios. Finish it first, so ENQUEUE_WAKEUP
can proceed as it would have sans DELAY_DEQUEUE treatment.

Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
Signed-off-by: Mike Galbraith <efault@xxxxxx>
---
kernel/sched/fair.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6049,10 +6049,14 @@ void unthrottle_cfs_rq(struct cfs_rq *cf
for_each_sched_entity(se) {
struct cfs_rq *qcfs_rq = cfs_rq_of(se);

- if (se->on_rq) {
- SCHED_WARN_ON(se->sched_delayed);
- break;
+ /* Handle any unfinished DELAY_DEQUEUE business first. */
+ if (unlikely(se->on_rq && se->sched_delayed)) {
+ int flags = DEQUEUE_SLEEP | DEQUEUE_SPECIAL;
+
+ dequeue_entity(qcfs_rq, se, flags | DEQUEUE_DELAYED);
}
+ if (se->on_rq)
+ break;
enqueue_entity(qcfs_rq, se, ENQUEUE_WAKEUP);

if (cfs_rq_is_idle(group_cfs_rq(se)))