Re: Shutdown-time hangs in -next in locktorture

[Paul E. McKenney]

On Sat, Dec 20, 2025 at 08:49:01AM -0800, Paul E. McKenney wrote:
> On Sat, Dec 20, 2025 at 01:52:01PM +0100, Peter Zijlstra wrote:
> > On Fri, Dec 19, 2025 at 04:29:26PM -0800, Paul E. McKenney wrote:
> > > Hello, Peter,
> > > 
> > > I started hitting shutdown-time hangs in next-20251217 which persist
> > > in next-20251219.  This hang happens on both x86 and arm64.  Once I
> > > figured out that the failure is high probability, but not deterministic,
> > > bisection converged here:
> > > 
> > > 5d1f0b2f278e ("sched/core: Rework sched_class::wakeup_preempt() and rq_modified_*()")
> > 
> > That commit no longer exists in tip/sched/core; it was fixed a few days
> > ago, except other problems made -next use an old tip branch which has
> > caused this fix to have delayed visibility :-(
> 
> Very good, I will retry later.

A bit later than I was planning, but here we are on next-20260113.  This
has a very similar failure on arm64 with that same repeat-by as before:

tools/testing/selftests/rcutorture/bin/torture.sh --duration 20 --do-none --do-normal --do-locktorture --do-kasan --configs-locktorture "LOCK09"

Bisection converges here:

704069649b5b ("sched/core: Rework sched_class::wakeup_preempt() and rq_modified_*()")

This commit does not revert cleanly, but retesting on both this commit
and the previous commit confirms the bisection result.

I have not yet checked this carefully on x86.

Or is this another case of stale commits in -next?  If not, please let
me know if there are debug options/patches that would be helpful.



							Thanx, Paul