transport-helper: fix TSAN race in transfer_debug()

Currently, transfer_debug() lazily initializes a static variable based
on GIT_TRANSLOOP_DEBUG. Since the function may be called from multiple
worker threads, this initialization is racy and is therefore suppressed
in .tsan-suppressions.

Initialize the variable in bidirectional_transfer_loop() before any
worker threads or processes are created. This patch removes the race and
allows dropping the corresponding TSAN suppression.

Signed-off-by: Pushkar Singh <pushkarkumarsingh1970@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/.tsan-suppressions b/.tsan-suppressions
index 5ba86d68459e61f87dae1332c7f2402860b4280c..d84883bd90f9a6cc44f505e4eeff44bb67c5b82b 100644 (file)
--- a/.tsan-suppressions
+++ b/.tsan-suppressions
@@ -7,7 +7,6 @@
 # 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$
 
 # A boolean value, which tells whether the replace_map has been initialized or
 # not, is read racily with an update. As this variable is written to only once,

diff --git a/transport-helper.c b/transport-helper.c
index 4614036c99a5a0464beb81a7b8e47e602074700c..8eee2de14bf20556ea3d8d9f742daef780b7ad42 100644 (file)
--- a/transport-helper.c
+++ b/transport-helper.c
@@ -1343,24 +1343,18 @@ int transport_helper_init(struct transport *transport, const char *name)
 /* This should be enough to hold debugging message. */
 #define PBUFFERSIZE 8192
 
+static int transfer_debug_enabled = -1;
+
 /* Print bidirectional transfer loop debug message. */
 __attribute__((format (printf, 1, 2)))
 static void transfer_debug(const char *fmt, ...)
 {
-       /*
-        * NEEDSWORK: This function is sometimes used from multiple threads, and
-        * we end up using debug_enabled racily. That "should not matter" since
-        * we always write the same value, but it's still wrong. This function
-        * is listed in .tsan-suppressions for the time being.
-        */
-
        va_list args;
        char msgbuf[PBUFFERSIZE];
-       static int debug_enabled = -1;
 
-       if (debug_enabled < 0)
-               debug_enabled = getenv("GIT_TRANSLOOP_DEBUG") ? 1 : 0;
-       if (!debug_enabled)
+       if (transfer_debug_enabled < 0)
+               BUG("somebody forgot to check GIT_TRANSLOOP_DEBUG!");
+       if (!transfer_debug_enabled)
                return;
 
        va_start(args, fmt);
@@ -1630,6 +1624,9 @@ int bidirectional_transfer_loop(int input, int output)
 {
        struct bidirectional_transfer_state state;
 
+       if (transfer_debug_enabled < 0)
+               transfer_debug_enabled = getenv("GIT_TRANSLOOP_DEBUG") ? 1 : 0;
+
        /* Fill the state fields. */
        state.ptg.src = input;
        state.ptg.dest = 1;