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5324953c06
Kernel test robot reported that tools/testing/selftests/kvm/hardware_disable_test was failing due to commit704069649b("sched/core: Rework sched_class::wakeup_preempt() and rq_modified_*()") It turns out there were two related problems that could lead to a missed preemption: - when hitting newidle balance from the idle thread, it would elevate rb->next_class from &idle_sched_class to &fair_sched_class, causing later wakeup_preempt() calls to not hit the sched_class_above() case, and not issue resched_curr(). Notably, this modification pattern should only lower the next_class, and never raise it. Create two new helper functions to wrap this. - when doing schedule_idle(), it was possible to miss (re)setting rq->next_class to &idle_sched_class, leading to the very same problem. Cc: Sean Christopherson <seanjc@google.com> Fixes:704069649b("sched/core: Rework sched_class::wakeup_preempt() and rq_modified_*()") Reported-by: kernel test robot <oliver.sang@intel.com> Closes: https://lore.kernel.org/oe-lkp/202602122157.4e861298-lkp@intel.com Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://patch.msgid.link/20260218163329.GQ1395416@noisy.programming.kicks-ass.net