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e51891a01d
With 4d9888c ("CLEANUP: fd: get rid of the __GET_{NEXT,PREV} macros") some
"volatile" keywords were dropped at various assignment places in fd's code.
In fd_add_to_fd_list() and fd_add_to_fd_list(), because of the absence of
the "volatile" keyword: the compiler was able to perform some code
optimizations that prevented prev and next variables from being reloaded
between locking attempts (goto loop).
The result was that fd_add_to_fd_list() and fd_rm_from_fd_list() could enter in
infinite loops, preventing other threads from working further and ultimately
resulting in the watchdog being triggered as described in GH #2011.
To fix this, we made sure to re-audit 4d9888c in order to restore the required
memory barriers / compilers hints to prevent the compiler from mis-optimizing
the code around the fd's locks.
That is: using atomic loads to fetch the prev and next values, and restoring
the "volatile" cast for cur_list.ent variable assignment in fd_rm_from_fd_list()
Big thanks to @xanaxalan for his help and patience and to @wtarreau for his
findings and explanations in regard to compiler's optimizations.
This must be backported in 2.7 with 4d9888c ("CLEANUP: fd: get rid of the
__GET_{NEXT,PREV} macros")
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)