• David J. Wilder's avatar
    IPoIB: Clear ipoib_neigh.dgid in ipoib_neigh_alloc() · 0cd4d0fd
    David J. Wilder authored
    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: default avatarDavid Wilder <dwilder@us.ibm.com>
    Signed-off-by: default avatarRoland Dreier <rolandd@cisco.com>
    0cd4d0fd
ipoib_main.c 35.8 KB