[PATCH 5/5] ThreadSanitizer: add suppressions

["Martin Ågren" <martin.agren@gmail.com>]

Add .tsan-suppressions for want_color() and transfer_debug(). Both of
these use the pattern

	static int foo = -1;
	if (foo == -1)
		foo = func();

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

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>
---
I am no memory-model expert. Maybe (aligned) stores and loads of int are
not actually atomic on all the various hardware that Git wants to run
on. Or maybe the compiler is allowed to compile them into 4 1-byte
accesses anyway...

 .tsan-suppressions | 12 ++++++++++++
 1 file changed, 12 insertions(+)
 create mode 100644 .tsan-suppressions

diff --git a/.tsan-suppressions b/.tsan-suppressions
new file mode 100644
index 000000000..910c02e59
--- /dev/null
+++ b/.tsan-suppressions
@@ -0,0 +1,12 @@
+# Suppressions for ThreadSanitizer (tsan).
+#
+# This file is used by setting the environment variable TSAN_OPTIONS to, e.g.,
+# "suppressions=$(pwd)/.tsan-suppressions". Observe that relative paths such as
+# ".tsan-suppressions" might not work.
+#
+# These suppressions can be, e.g., that a static variable is written to and it
+# is always the same value being written, so it doesn't really matter that two
+# or more such writes race.
+
+race:^want_color$
+race:^transfer_debug$
-- 
2.14.1.151.gdfeca7a7e