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.
Also, if you do that can you get rid of the ifdef? If it really *really*
mattered, we could introduce smp_mb before/after xchg... but if you
use smp_wmb anyway then it definitely does not matter because that is a
noop on x86.
Thanks,
Nick
>
Cc: Samuel Thibault <samuel.thibault@xxxxxxxxxxxxx>
> Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
> ---
> drivers/xen/events.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index 73d78dc..332dd63 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -529,7 +529,7 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
>
> #ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86.
> */ /* Clear master flag /before/ clearing selector flag. */
> - rmb();
> + wmb();
> #endif
> pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0);
> while (pending_words != 0) {
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