[lttng-dev] [PATCH 00/11] Add support for TSAN to liburcu

Olivier Dion odion at efficios.com
Tue May 23 12:05:07 EDT 2023

Hi Dmitry,

We do have a new issue and we think it might be a limitation from TSAN.

Find attached a test program that we believe is correct.  You can
compile it with `gcc -fsanitize=thread test.c -pthread'.

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TSAN flags a race condition between the atomic store relaxed at line 36
and the free at line 81.

We can solve the issue by replacing the atomic store relaxed with a
atomic store release.  However, the preceding atomic exchange with
sequential consistency already acts as an implicit release (in term of
memory barrier) for the following store, making the release semantic

We've found an alternative to fix this by ignoring the thread during the
relaxed store (line 39).  However, what we would like is to annotate the
memory stored (line 45).

My theory (I don't know the internal of TSAN much) is that TSAN thinks
for some reason that the atomic store relaxed happen at the same epoch
as the free, resulting in a false positive.  If so, m


Olivier Dion
EfficiOS Inc.

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