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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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