On Thu, 03 Sep 2026 13:10:36 +0530, Athira Rajeev wrote:
> commit 79104becf42b ("sched/fair: Forfeit vruntime on yield") changed
> yield_task_fair() to only bump the deadline when the entity is eligible
> (vruntime <= avg_vruntime). When the entity is ineligible the yield
> becomes a complete no-op from scheduling perspective.
>
> lost_exception_test calls sched_yield() 100,000 times per iteration to
> race the EBB exception delivery with a context switch to the eat_cpu
> companion process. After enough iterations the test process's vruntime
> races ahead of avg_vruntime (each eligible yield bumps vruntime to
> deadline, then advances deadline by one slice). Once ineligible,
> yield_task_fair() does nothing: so the scheduler won't pick the
> eat_cpu child. No context switch occurs, the PMAO race is never
> triggered, and ebb_count stays at 0 forever causing the test to
> hang until timeout.
>
> [...]
Applied to powerpc/fixes.
[1/1] selftests/powerpc/pmu/ebb: fix lost_exception_test hang with sched yield
change
https://git.kernel.org/powerpc/c/ef17515a8ef88c246c342a6c532aa10f9ecdcfaf
cheers
