From 97a545ab6ce922a0f868d192718a48a0091ebc5e Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty@rustcorp.com.au>
Date: Wed, 24 Feb 2010 14:22:22 -0600
Subject: [PATCH] virtio: remove bogus barriers from DEBUG version of
virtio_ring.c
With DEBUG defined, we add an ->in_use flag to detect if the caller
invokes two virtio methods in parallel. The barriers attempt to ensure
timely update of the ->in_use flag.
But they're voodoo: if we need these barriers it implies that the
calling code doesn't have sufficient synchronization to ensure the
code paths aren't invoked at the same time anyway, and we want to
detect it.
Also, adding barriers changes timing, so turning on debug has more
chance of hiding real problems.
Thanks to MST for drawing my attention to this code...
CC: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
---
drivers/virtio/virtio_ring.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index fbd2ecde93e4..1ee97d402a48 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -36,10 +36,9 @@
panic("%s:in_use = %i\n", \
(_vq)->vq.name, (_vq)->in_use); \
(_vq)->in_use = __LINE__; \
- mb(); \
} while (0)
#define END_USE(_vq) \
- do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; mb(); } while(0)
+ do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
#else
#define BAD_RING(_vq, fmt, args...) \
do { \
--
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