[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: [PATCH] Fix memory order issue inside pv spinlock
On 09/09/09 09:30, Yang, Xiaowei wrote: > Jeremy Fitzhardinge wrote: >> On 09/07/09 00:40, Yang, Xiaowei wrote: >>> barrier() can't prevent reads after it not being reordered with older >>> writes to different locates before it. Because of it, I can't bring up >>>> 4 HVM guests on one SMP machine. Use mb() instead. >> >> Which read is happening too early? Is it "xl->spinners"? How does >> it fail? > > Yes. If read of xl->spinners happens earlier than write 0 to xl->lock, > notifications to wake up other spinners can be omitted incorrectly, > resulting in others polling indefinitely (because of poll evtchn not > pending) with the lock is uncontended. OK. And the CPU only guarantees that, without explicit barriers, write-read ordering is only maintained between accesses to the same memory location, not separate locations? J _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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