• Peter Zijlstra's avatar
    sched: Replace rq::wake_list · a1488664
    Peter Zijlstra authored
    The recent commit: 90b5363a ("sched: Clean up scheduler_ipi()")
    got smp_call_function_single_async() subtly wrong. Even though it will
    return -EBUSY when trying to re-use a csd, that condition is not
    atomic and still requires external serialization.
    
    The change in ttwu_queue_remote() got this wrong.
    
    While on first reading ttwu_queue_remote() has an atomic test-and-set
    that appears to serialize the use, the matching 'release' is not in
    the right place to actually guarantee this serialization.
    
    The actual race is vs the sched_ttwu_pending() call in the idle loop;
    that can run the wakeup-list without consuming the CSD.
    
    Instead of trying to chain the lists, merge them.
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Link: https://lore.kernel.org/r/20200526161908.129371594@infradead.org
    a1488664
idle.c 11.3 KB