• Sebastian Andrzej Siewior's avatar
    sched/core: Remove get_cpu() from sched_fork() · af0fffd9
    Sebastian Andrzej Siewior authored
    get_cpu() disables preemption for the entire sched_fork() function.
    This get_cpu() was introduced in commit:
    
      dd41f596 ("sched: cfs core code")
    
    ... which also invoked sched_balance_self() and this function
    required preemption do be off.
    
    Today, sched_balance_self() seems to be moved to ->task_fork callback
    which is invoked while the ->pi_lock is held.
    
    set_load_weight() could invoke reweight_task() which then via $callchain
    might end up in smp_processor_id() but since `update_load' is false
    this won't happen.
    
    I didn't find any this_cpu*() or similar usage during the initialisation
    of the task_struct.
    
    The `cpu' value (from get_cpu()) is only used later in __set_task_cpu()
    while the ->pi_lock lock is held.
    
    Based on this it is possible to remove get_cpu() and use
    smp_processor_id() for the `cpu' variable without breaking anything.
    Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/20180706130615.g2ex2kmfu5kcvlq6@linutronix.deSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    af0fffd9
core.c 173 KB