99d6c889d0
On ARM with 80 cores and a single server, it's sometimes possible to see a segfault in fwlc_get_next_server() around 600-700k RPS. It seldom happens as well on x86 with 128 threads with the same config around 1M rps. It turns out that in fwlc_get_next_server(), before calling fwlc_srv_reposition(), we have to drop the lock and that one takes it back again. The problem is that anything can happen to our node during this time, and it can be freed. Then when continuing our work, we later iterate over it and its next to find a node with an acceptable key, and by doing so we can visit either uninitialized memory or simply nodes that are no longer in the tree. A first attempt at fixing this consisted in artificially incrementing the elements count before dropping the lock, but that turned out to be even worse because other threads could loop forever on such an element looking for an entry that does not exist. Maintaining a separate refcount didn't work well either, and it required to deal with the memory release while dropping it, which is really not convenient. Here we're taking a different approach consisting in simply not trusting this node anymore and going back to the beginning of the loop, as is done at a few other places as well. This way we can safely ignore the possibly released node, and the test runs reliably both on the arm and the x86 platforms mentioned above. No performance regression was observed either, likely because this operation is quite rare. No backport is needed since this appeared with the leastconn rework in 3.2. |
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HAProxy
HAProxy is a free, very fast and reliable reverse-proxy offering high availability, load balancing, and proxying for TCP and HTTP-based applications.
Installation
The INSTALL file describes how to build HAProxy. A list of packages is also available on the wiki.
Getting help
The discourse and the mailing-list are available for questions or configuration assistance. You can also use the slack or IRC channel. Please don't use the issue tracker for these.
The issue tracker is only for bug reports or feature requests.
Documentation
The HAProxy documentation has been split into a number of different files for ease of use. It is available in text format as well as HTML. The wiki is also meant to replace the old architecture guide.
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)
License
HAProxy is licensed under GPL 2 or any later version, the headers under LGPL 2.1. See the LICENSE file for a more detailed explanation.