Re: [PATCH 00/14] sched: Support shared runqueue locking

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Sep 10, 2025 at 07:32:12PM +0200, Andrea Righi wrote:

> I've done a quick test with this patch set applied and I was able to
> trigger this:
> 
> [   49.746281] ============================================
> [   49.746457] WARNING: possible recursive locking detected
> [   49.746559] 6.17.0-rc4-virtme #85 Not tainted
> [   49.746666] --------------------------------------------
> [   49.746763] stress-ng-race-/5818 is trying to acquire lock:
> [   49.746856] ffff890e0adacc18 (&dsq->lock){-.-.}-{2:2}, at: dispatch_dequeue+0x125/0x1f0
> [   49.747052]
> [   49.747052] but task is already holding lock:
> [   49.747234] ffff890e0adacc18 (&dsq->lock){-.-.}-{2:2}, at: task_rq_lock+0x6c/0x170
> [   49.747416]
> [   49.747416] other info that might help us debug this:
> [   49.747557]  Possible unsafe locking scenario:
> [   49.747557]
> [   49.747689]        CPU0
> [   49.747740]        ----
> [   49.747793]   lock(&dsq->lock);
> [   49.747867]   lock(&dsq->lock);
> [   49.747950]
> [   49.747950]  *** DEADLOCK ***
> [   49.747950]
> [   49.748086]  May be due to missing lock nesting notation
> [   49.748086]
> [   49.748197] 3 locks held by stress-ng-race-/5818:
> [   49.748335]  #0: ffff890e0f0fce70 (&p->pi_lock){-.-.}-{2:2}, at: task_rq_lock+0x38/0x170
> [   49.748474]  #1: ffff890e3b6bcc98 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x20/0xa0
> [   49.748652]  #2: ffff890e0adacc18 (&dsq->lock){-.-.}-{2:2}, at: task_rq_lock+0x6c/0x170
> 
> Reproducer:
> 
>  $ cd tools/sched_ext
>  $ make scx_simple
>  $ sudo ./build/bin/scx_simple
>  ... and in another shell
>  $ stress-ng --race-sched 0

Heh, the selftests thing was bound to not cover everything. I'll have a
poke at it. Thanks!