From efc71a3c132be05461ffc872e70390d61f27bc7e Mon Sep 17 00:00:00 2001
From: Ben Wagner <bungeman@chromium.org>
Date: Tue, 31 Aug 2021 12:47:48 -0400
Subject: [PATCH] Free local FcCache lock on contention

If two threads attempt to create the FcCache lock in lock_cache at the
same time, both threads may create and initialize a local FcMutex. One
thread will atomically make cache_lock point to its FcMutex. The other
thread currently calls FcMutexFinish on the local lock, but does not
free it. Change this behavior to free the unused lock.

Found with test/test-pthread on an LeakSanitizer enabled build.
---
 src/fccache.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/fccache.c b/src/fccache.c
index d8ffe09..4a6a752 100644
--- a/src/fccache.c
+++ b/src/fccache.c
@@ -495,6 +495,7 @@ retry:
     FcMutexInit (lock);
     if (!fc_atomic_ptr_cmpexch (&cache_lock, NULL, lock)) {
       FcMutexFinish (lock);
+      free (lock);
       goto retry;
     }