• Mike Galbraith's avatar
    Sched: fix skip_clock_update optimization · f26f9aff
    Mike Galbraith authored
    idle_balance() drops/retakes rq->lock, leaving the previous task
    vulnerable to set_tsk_need_resched().  Clear it after we return
    from balancing instead, and in setup_thread_stack() as well, so
    no successfully descheduled or never scheduled task has it set.
    
    Need resched confused the skip_clock_update logic, which assumes
    that the next call to update_rq_clock() will come nearly immediately
    after being set.  Make the optimization robust against the waking
    a sleeper before it sucessfully deschedules case by checking that
    the current task has not been dequeued before setting the flag,
    since it is that useless clock update we're trying to save, and
    clear unconditionally in schedule() proper instead of conditionally
    in put_prev_task().
    Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
    Reported-by: default avatarBjoern B. Brandenburg <bbb.lst@gmail.com>
    Tested-by: default avatarYong Zhang <yong.zhang0@gmail.com>
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: stable@kernel.org
    LKML-Reference: <1291802742.1417.9.camel@marge.simson.net>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    f26f9aff
fork.c 42.1 KB