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[Qemu-devel] [PATCH] xenfb: Fix overzealous ring test

From: Samuel Thibault
Subject: [Qemu-devel] [PATCH] xenfb: Fix overzealous ring test
Date: Mon, 18 Apr 2016 14:41:48 +0200

From: Wei Liu <address@hidden>

pv-grub booting got broken with recent qemu-xen, due to
ac0487e1d2ae811cd4d035741a109a4ecfb013f1 ('xenfb.c: avoid expensive loops
when prod <= out_cons')

prod - out_cons can actually be XENFB_OUT_RING_LEN when the ring is exactly
full, this is a normal condition and should not be excluded.

From: Wei Liu <address@hidden>
Signed-off-by: Samuel Thibault <address@hidden>
Tested-by: Hao Xudong <address@hidden>
 hw/display/xenfb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c
index 40b096a..9866dfd 100644
--- a/hw/display/xenfb.c
+++ b/hw/display/xenfb.c
@@ -775,7 +775,7 @@ static void xenfb_handle_events(struct XenFB *xenfb)
     prod = page->out_prod;
     out_cons = page->out_cons;
-    if (prod - out_cons >= XENFB_OUT_RING_LEN) {
+    if (prod - out_cons > XENFB_OUT_RING_LEN) {
     xen_rmb();         /* ensure we see ring contents up to prod */

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