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This is the h1 equivalent of previous "BUG/MEDIUM: mux-h2: fail earlier
on malloc in takeover()".
Connection takeover was implemented for H1 in 2.2 by commit f12ca9f8f1
("MEDIUM: mux_h1: Implement the takeover() method."). It does have one
corner case related to memory allocation failure: in case the task or
tasklet allocation fails, the connection gets released synchronously.
Unfortunately the situation is bad there, because the lower layers are
already switched to the new thread while the tasklet is either NULL or
still the old one, and calling h1_release() will call some unsubscribe
and and possibly other things whose safety is not guaranteed (and the
ambiguity here alone is sufficient to be careful). There are even code
paths where the thread will try to grab the lock of its own idle conns
list, believing the connection is there while it has no useful effect.
However, if the owner thread was doing the same at the same moment, and
ended up trying to pick from the current thread (which could happen if
picking a connection for a different name), the two could even deadlock.
Contrary to mux-h2, a few tests were not sufficient to try to crash the
process, but there's nothing that indicates it couldn't happen based on
the description above.
This patch takes a simple but radically different approach. Instead of
starting to migrate the connection before risking to face allocation
failures, it first pre-allocates a new task and tasklet, then assigns
them to the connection if the migration succeeds, otherwise it just
frees them. This way it's no longer needed to manipulate the connection
until it's fully migrated, and as a bonus this means the connection will
continue to exist and the use-after-free condition is solved at the same
time.
This should be backported to 2.2. Thanks to Fred for the initial analysis
of the problem!
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)