Re: [PATCHSET sched_ext/for-7.0-fixes] sched_ext: Fix SCX_KICK_WAIT deadlock

[Christian Loehle <christian.loehle@arm.com>]

On 3/29/26 00:18, Tejun Heo wrote:
> Hello,
> 
> SCX_KICK_WAIT busy-waits in kick_cpus_irq_workfn() until the target CPU
> reschedules. Because the irq_work runs in hardirq context, the waiting
> CPU's kick_sync never advances, and if multiple CPUs form a wait cycle, all
> deadlock. This was reported by Christian while testing on arm64.
> 
> 0001 fixes the deadlock by deferring the wait to a balance callback which
> drops the rq lock and enables IRQs, allowing IPIs to be processed and
> kick_sync to keep advancing during the wait.
> 
> 0002 adds a selftest that creates a 3-CPU kick_wait cycle to reproduce the
> issue.
> 
> Based on sched_ext/for-7.0-fixes (db08b1940f4b).
> 
>  0001-sched_ext-Fix-SCX_KICK_WAIT-deadlock-by-deferring-wa.patch
>  0002-selftests-sched_ext-Add-cyclic-SCX_KICK_WAIT-stress-.patch
> 
>  kernel/sched/ext.c                                 |  95 +++++++---
>  kernel/sched/sched.h                               |   3 +
>  tools/testing/selftests/sched_ext/Makefile         |   1 +
>  .../selftests/sched_ext/cyclic_kick_wait.bpf.c     |  68 ++++++++
>  .../testing/selftests/sched_ext/cyclic_kick_wait.c | 194 +++++++++++++++++++++
>  5 files changed, 336 insertions(+), 25 deletions(-)
> 
> --
> tejun

For both:
Tested-by: Christian Loehle <christian.loehle@arm.com>

Thanks for fixing this!