[RELEASE] LTTng-UST 2.9.7 (EOL), 2.10.6 (Linux user-space tracer)

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We are pleased to announce the 2.9.7 (EOL) and 2.10.6 stable releases
of the LTTng-UST 2.9 and 2.10 stable branches.

LTTng-UST, the Linux Trace Toolkit Next Generation Userspace Tracer,
is a low-overhead application tracer. The library "liblttng-ust" enables
tracing of applications and libraries.

* New in this release:

Important fixes to the lttng-ust fd tracker (liblttng-ust-fd.so) were done,
taking care of locking the fd tracker across fork() in the liblttng-ust-fork.so
wrapper, eliminating hangs observed in the child if the parent was executing
close() concurrently with fork(). Also, given that close() is an async-signal-safe
function, ensure that the synchronization strategy is robust against signals
by disabling signals and using a TLS nesting counter when taking the fd tracker
lock. [1, 2]

Another important fix to the lttng-ust fd tracker is disabling thread
cancellation around fd tracker lock, and locking the fd tracker across
fork() in the liblttng-ust-fork.so wrapper. Failure to do so causes
deadlocks in child applications if a pthread cancellation is performed
on a thread while it ran the liblttng-ust-fd close(3) wrapper. [3]

The locking strategy of the LTTng perf counter contexts was revisited to
eliminate a deadlock occurring once in a while when using the perf counters
context with lttng-ust. [4]

Now that the release of LTTng-UST 2.11.0 is imminent, version 2.9.7 marks
the end of life (EOL) of the 2.9 stable branch of LTTng-UST.



Project website: http://lttng.org
Documentation: http://lttng.org/docs
Download link: http://lttng.org/download

[1] https://bugs.lttng.org/issues/1199
[2] https://bugs.lttng.org/issues/1200
[3] https://bugs.lttng.org/issues/1201
[4] https://bugs.lttng.org/issues/1202

Mathieu Desnoyers
EfficiOS Inc.

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