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Re: [Xen-devel] [PATCH] fix event channel notification loss on IA64

On 29 Jun 2006, at 06:43, Isaku Yamahata wrote:

evtchn_do_upcall() has a micro optimization which is depends on
that xchg is a barrier.
However xchg of IA64 has acquire semantics so that event
channel notification is lost sometimes. This patch fixes it.

clear_bit() isn't a barrier either (at least according to Linux bitop semantics). You want 'rmb();'. I suggest just putting it inside ifndef CONFIG_X86, with the comment about XCHG being a barrier on x86 placed just before the ifndef. Leave the zap of pending flag as a plain write.

 -- Keir

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