[Xen-changelog] [xen-unstable] evtchn_do_upcall() has a micro optimization which is depends on that xchg is a barrier.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID c9696012fe05347ad6a0d503bc55b53b76783af3
# Parent  5db7bbccf4d2d759265415085fa81094893f60a9
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.

Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>
---
 linux-2.6-xen-sparse/drivers/xen/core/evtchn.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletion(-)

diff -r 5db7bbccf4d2 -r c9696012fe05 
linux-2.6-xen-sparse/drivers/xen/core/evtchn.c
--- a/linux-2.6-xen-sparse/drivers/xen/core/evtchn.c    Fri Jun 30 10:04:22 
2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/core/evtchn.c    Fri Jun 30 10:07:38 
2006 +0100
@@ -219,7 +219,10 @@ asmlinkage void evtchn_do_upcall(struct 
 
        vcpu_info->evtchn_upcall_pending = 0;
 
-       /* NB. No need for a barrier here -- XCHG is a barrier on x86. */
+#ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. */
+       /* Clear master pending flag /before/ clearing selector flag. */
+       rmb();
+#endif
        l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);
        while (l1 != 0) {
                l1i = __ffs(l1);

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