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IPoIB can miss a change in destination GID under some conditions. The
problem is caused when ipoib_neigh->dgid contains a stale address.
The fix is to set ipoib_neigh->dgid to zero in ipoib_neigh_alloc().
This can happen when a system using bonding on its IPoIB interfaces
has switched its active interface from interface A to B and back to A.
The system that fails over will not correctly processes the 2nd
address change, as described below.
When an address has changed neighbor->ha is updated with the new
address. Each neighbor has an associated ipoib_neigh.
ipoib_neigh->dgid also holds a copy of the remote node's hardware
address. When an address changes neighbor->ha is updated by the
network layer (arp code) with the new address. IPoIB detects this
change in ipoib_start_xmit() by comparing neighbor->ha with
ipoib_neigh->dgid. The bug is that ipoib_neigh->dgid may already
contain the new address (A) thus the change from B to A is missed by
ipoib. Here is the sequence of events:
ipoib_neigh->dgid = A and neighbor->ha = A
The address is switched to B (the first switch)
neighbor->ha = B
The change is seen in ipoib_start_xmit() -- neighbor->ha !=
ipoib_neigh->dgid so ipoib_neigh is released, and a new one is
allocated.
The allocator may return the same chunk of memory that was just
released, therefore ipoib_neigh->dgid still contains A at this point.
ipoib_neigh->dgid should be updated in neigh_add_path(), but if the
following conditions are true dgid is not updated:
1) __path_find() returns a path
2) path->ah is NULL
The remote system now switches from address B to A, neighbor->ha is
updated to A.
Now we have again : ipoib_neigh->dgid = A and neighbor->ha = A
Since the addresses are the same ipoib won't process the change in
address. Fix this by zeroing out the dgid field when allocating a new
struct ipoib_neigh.
Signed-off-by: David Wilder <dwilder@us.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
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