On 10/23, Paul E. McKenney wrote: > > * Note that this guarantee implies a further memory-ordering guarantee. > * On systems with more than one CPU, when synchronize_sched() returns, > * each CPU is guaranteed to have executed a full memory barrier since > * the end of its last RCU read-side critical section ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Ah wait... I misread this comment. But this patch needs more? Or I misunderstood. There is no RCU unlock in percpu_up_read(). IOW. Suppose the code does percpu_down_read(); x = PROTECTED_BY_THIS_RW_SEM; percpu_up_read(); Withoit mb() the load above can be reordered with this_cpu_dec() in percpu_up_read(). However, we do not care if we can guarantee that the next percpu_down_write() can not return (iow, the next "write" section can not start) until this load is complete. And I _think_ that another synchronize_sched() in percpu_down_write() added by this patch should work. But, "since the end of its last RCU read-side critical section" does not look enough. Or I misundersood you/Mikulas/both ? Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/