[Xen-changelog] [xen-3.0-testing] [NET] back: fix synchronisation of access to deallocation buffer ring.

[Xen patchbot-3.0-testing <patchbot-3.0-testing@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID e1a85211281f7f2097a3d400b0b3db90e5da2ff6
# Parent  e8a45450a48dd588b8c0ba06a85dd3f5f5157f8e
[NET] back: fix synchronisation of access to deallocation buffer ring.
Must ensure ring is written to before producer index is incremented.
Bug diagnosed by Ky Srinivasan <ksrinivasan@xxxxxxxxxx>
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
xen-unstable changeset:   10268:9f50b8c2de0ad641d7795613edc35d78240dab8c
xen-unstable date:        Mon Jun  5 15:14:58 2006 +0100
---
 linux-2.6-xen-sparse/drivers/xen/netback/netback.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletion(-)

diff -r e8a45450a48d -r e1a85211281f 
linux-2.6-xen-sparse/drivers/xen/netback/netback.c
--- a/linux-2.6-xen-sparse/drivers/xen/netback/netback.c        Mon Jun 05 
10:44:07 2006 +0100
+++ b/linux-2.6-xen-sparse/drivers/xen/netback/netback.c        Mon Jun 05 
15:15:45 2006 +0100
@@ -452,6 +452,9 @@ inline static void net_tx_action_dealloc
        dc = dealloc_cons;
        dp = dealloc_prod;
 
+       /* Ensure we see all indexes enqueued by netif_idx_release(). */
+       smp_rmb();
+
        /*
         * Free up any grants we have finished using
         */
@@ -689,7 +692,10 @@ static void netif_idx_release(u16 pendin
        unsigned long flags;
 
        spin_lock_irqsave(&_lock, flags);
-       dealloc_ring[MASK_PEND_IDX(dealloc_prod++)] = pending_idx;
+       dealloc_ring[MASK_PEND_IDX(dealloc_prod)] = pending_idx;
+       /* Sync with net_tx_action_dealloc: insert idx /then/ incr producer. */
+       smp_wmb();
+       dealloc_prod++;
        spin_unlock_irqrestore(&_lock, flags);
 
        tasklet_schedule(&net_tx_tasklet);

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