ThreadSanitizer: add suppressions

Add a file .tsan-suppressions and list two functions in it: want_color()
and transfer_debug(). Both of these use the pattern

	static int foo = -1;
	if (foo < 0)
		foo = bar();

where bar always returns the same non-negative value. This can cause
ThreadSanitizer to diagnose a race when foo is written from two threads.
That is indeed a race, although it arguably doesn't matter in practice
since it's always the same value that is written.

Add NEEDSWORK-comments to the functions so that this problem is not
forever swept way under the carpet.

The suppressions-file is used by setting the environment variable
TSAN_OPTIONS to, e.g., "suppressions=$(pwd)/.tsan-suppressions". Observe
that relative paths such as ".tsan-suppressions" might not work.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/.tsan-suppressions b/.tsan-suppressions
new file mode 100644
index 0000000000..8c85014a0a
--- /dev/null
+++ b/.tsan-suppressions
@@ -0,0 +1,10 @@
+# Suppressions for ThreadSanitizer (tsan).
+#
+# This file is used by setting the environment variable TSAN_OPTIONS to, e.g.,
+# "suppressions=$(pwd)/.tsan-suppressions". Observe that relative paths such as
+# ".tsan-suppressions" might not work.
+
+# A static variable is written to racily, but we always write the same value, so
+# in practice it (hopefully!) doesn't matter.
+race:^want_color$
+race:^transfer_debug$