• Peter Zijlstra's avatar
    sched: Fix balance vs hotplug race · 6ad4c188
    Peter Zijlstra authored
    Since (e761b772: cpu hotplug, sched: Introduce cpu_active_map and redo
    sched domain managment) we have cpu_active_mask which is suppose to rule
    scheduler migration and load-balancing, except it never (fully) did.
    
    The particular problem being solved here is a crash in try_to_wake_up()
    where select_task_rq() ends up selecting an offline cpu because
    select_task_rq_fair() trusts the sched_domain tree to reflect the
    current state of affairs, similarly select_task_rq_rt() trusts the
    root_domain.
    
    However, the sched_domains are updated from CPU_DEAD, which is after the
    cpu is taken offline and after stop_machine is done. Therefore it can
    race perfectly well with code assuming the domains are right.
    
    Cure this by building the domains from cpu_active_mask on
    CPU_DOWN_PREPARE.
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    LKML-Reference: <new-submission>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    6ad4c188
cpumask.h 25.3 KB