Messages in this thread | | | Date | Wed, 11 Jun 2008 07:54:51 +0100 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH] xen: Use wmb instead of rmb in xen_evtchn_do_upcall(). |
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Nick Piggin wrote: > On Tuesday 10 June 2008 17:57, Jeremy Fitzhardinge wrote: > >> Nick Piggin wrote: >> >>> On Tuesday 10 June 2008 17:35, Isaku Yamahata wrote: >>> >>>> This patch is ported one from 534:77db69c38249 of linux-2.6.18-xen.hg. >>>> Use wmb instead of rmb to enforce ordering between >>>> evtchn_upcall_pending and evtchn_pending_sel stores >>>> in xen_evtchn_do_upcall(). >>>> >>> There are a whole load of places in the kernel that should be using >>> smp_ variants of memory barriers. This seemed to me like one of them, >>> but I could be wrong. >>> >> No, it needs to be an unconditional barrier. This is synchronizing with >> the hypervisor - even if the kernel is compiled UP, the SMP hypervisor >> may be testing/setting the events pending bits from another (physical) cpu. >> > > OK. What you *really* want is smp_*mb_even_if_compiled_for_UP() ;) > That is, a small set of primitives that are compiled with CONFIG_SMP > (and given some xxx_ prefix to distinguish). >
We already have a set of sync_* for atomic ops which are always locked.
> IO barriers are probably the best thing you can use for the moment. >
It is conceptually similar, I suppose.
J
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