Re: Why a “barrier()” is enough for disabling or enabling the preemption?

Doug Wilson doug.lkml at
Mon Nov 30 04:36:21 EST 2015

> #define preempt_disable() barrier()
> ......
> #define preempt_enable() barrier()

  Let me try answering this with a limited knowledge I have about barriers.
barrier() essentially was added so that compiler reordering does not happen.

  In the code above, since the compiler does not know/understand the
specialty of preempt_[enable/disable], the compiler might decide to change
the ordering.

 In this case, where the code is disabling/enabling preemption, barrier() tells
the compiler that it can't move stuff around.

 I hope this helps.

- Doug

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