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There is a very short race in the queues which happens in the following
situation:
- stream A on thread 1 is being processed by a server
- stream B on thread 2 waits in the backend queue for a server
- stream B on thread 2 is fed up with waiting and expires, calls
stream_free() which calls pendconn_free(), which sees the
stream attached
- at the exact same instant, stream A finishes on thread 1, sees
one stream is waiting (B), detaches it and wakes it up
- stream B continues pendconn_free() and calls pendconn_unlink()
- pendconn_unlink() now detaches the node again and performs a
second deletion (harmless since idempotent), and decrements
srv/px->nbpend again
=> the number of connections on the proxy or server may reach -1 if/when
this race occurs.
It is extremely tight as it can only occur during the test on p->leaf_p
though it has been witnessed at least once. The solution consists in
testing leaf_p again once the lock is held to make sure the element was
not removed in the mean time.
This should be backported to 2.0 and 1.9, probably even 1.8.
The HAProxy documentation has been split into a number of different files for ease of use. Please refer to the following files depending on what you're looking for : - INSTALL for instructions on how to build and install HAProxy - BRANCHES to understand the project's life cycle and what version to use - LICENSE for the project's license - CONTRIBUTING for the process to follow to submit contributions The more detailed documentation is located into the doc/ directory : - doc/intro.txt for a quick introduction on HAProxy - doc/configuration.txt for the configuration's reference manual - doc/lua.txt for the Lua's reference manual - doc/SPOE.txt for how to use the SPOE engine - doc/network-namespaces.txt for how to use network namespaces under Linux - doc/management.txt for the management guide - doc/regression-testing.txt for how to use the regression testing suite - doc/peers.txt for the peers protocol reference - doc/coding-style.txt for how to adopt HAProxy's coding style - doc/internals for developer-specific documentation (not all up to date)