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tipc: introduce node contact FSM

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The logics for determining when a node is permitted to establish
and maintain contact with its peer node becomes non-trivial in the
presence of multiple parallel links that may come and go independently.

A known failure scenario is that one endpoint registers both its links
to the peer lost, cleans up it binding table, and prepares for a table
update once contact is re-establihed, while the other endpoint may
see its links reset and re-established one by one, hence seeing
no need to re-synchronize the binding table. To avoid this, a node
must not allow re-establishing contact until it has confirmation that
even the peer has lost both links.

Currently, the mechanism for handling this consists of setting and
resetting two state flags from different locations in the code. This
solution is hard to understand and maintain. A closer analysis even
reveals that it is not completely safe.

In this commit we do instead introduce an FSM that keeps track of
the conditions for when the node can establish and maintain links.
It has six states and four events, and is strictly based on explicit
knowledge about the own node's and the peer node's contact states.
Only events leading to state change are shown as edges in the figure
below.

                             +--------------+
                             | SELF_UP/     |
           +---------------->| PEER_COMING  |-----------------+
    SELF_  |                 +--------------+                 |PEER_
    ESTBL_ |                        |                         |ESTBL_
    CONTACT|      SELF_LOST_CONTACT |                         |CONTACT
           |                        v                         |
           |                 +--------------+                 |
           |      PEER_      | SELF_DOWN/   |     SELF_       |
           |      LOST_   +--| PEER_LEAVING |<--+ LOST_       v
+-------------+   CONTACT |  +--------------+   | CONTACT  +-----------+
| SELF_DOWN/  |<----------+                     +----------| SELF_UP/  |
| PEER_DOWN   |<----------+                     +----------| PEER_UP   |
+-------------+   SELF_   |  +--------------+   | PEER_    +-----------+
           |      LOST_   +--| SELF_LEAVING/|<--+ LOST_       A
           |      CONTACT    | PEER_DOWN    |     CONTACT     |
           |                 +--------------+                 |
           |                         A                        |
    PEER_  |       PEER_LOST_CONTACT |                        |SELF_
    ESTBL_ |                         |                        |ESTBL_
    CONTACT|                 +--------------+                 |CONTACT
           +---------------->| PEER_UP/     |-----------------+
                             | SELF_COMING  |
                             +--------------+

Reviewed-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jon Paul Maloy 2015-07-16 16:54:30 -04:00 • committed by David S. Miller
parent 8a1577c96f
commit 1a20cc254e
4 changed files with 185 additions and 54 deletions
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7
net/tipc/msg.h
View file

@ -766,6 +766,13 @@ static inline void msg_set_link_tolerance(struct tipc_msg *m, u32 n)
msg_set_bits(m, 9, 0, 0xffff, n);
}
static inline bool msg_peer_is_up(struct tipc_msg *m)
{
if (likely(msg_user(m) != LINK_PROTOCOL) || (msg_type(m) == STATE_MSG))
return true;
return msg_redundant_link(m);
}
struct sk_buff *tipc_buf_acquire(u32 size);
bool tipc_msg_validate(struct sk_buff *skb);
bool tipc_msg_reverse(u32 own_addr, struct sk_buff *buf, u32 *dnode,