I understand that DSB, DMB, and ISB are barriers for prevent reordering of instructions. I also can find lots of very good explanations for each of them, but it is pretty hard to imagine the case that I have to use them.

Also, from the open source codes, I see those barriers from time to time, but it is quite hard to understand why they are used. Just for an example, in Linux kernel 3.7 tcp_rcv_synsent_state_process function, there is a line as follows:

    if (unlikely(po->origdev))
            sll->sll_ifindex = orig_dev->ifindex;
    else
            sll->sll_ifindex = dev->ifindex;

    smp_mb();

    if (po->tp_version <= TPACKET_V2)
            __packet_set_status(po, h.raw, status);

where smp_mb() is basically DMB. Could you give me some of your real-life examples? It would help understand more about barriers.

arm barrier
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