Index: compiler-rt/lib/profile/GCDAProfiling.c
===================================================================
--- compiler-rt/lib/profile/GCDAProfiling.c
+++ compiler-rt/lib/profile/GCDAProfiling.c
@@ -348,20 +348,29 @@
   fd = open(filename, O_RDWR | O_BINARY);
 
   if (fd == -1) {
-    /* Try opening the file, creating it if necessary. */
-    new_file = 1;
-    mode = "w+b";
-    fd = open(filename, O_RDWR | O_CREAT | O_BINARY, 0644);
-    if (fd == -1) {
+    /* Try creating the file. */
+    fd = open(filename, O_RDWR | O_CREAT | O_EXCL | O_BINARY, 0644);
+    if (fd != -1) {
+      new_file = 1;
+      mode = "w+b";
+    } else {
       /* Try creating the directories first then opening the file. */
       __llvm_profile_recursive_mkdir(filename);
-      fd = open(filename, O_RDWR | O_CREAT | O_BINARY, 0644);
-      if (fd == -1) {
-        /* Bah! It's hopeless. */
-        int errnum = errno;
-        fprintf(stderr, "profiling: %s: cannot open: %s\n", filename,
-                strerror(errnum));
-        return;
+      fd = open(filename, O_RDWR | O_CREAT | O_EXCL | O_BINARY, 0644);
+      if (fd != -1) {
+        new_file = 1;
+        mode = "w+b";
+      } else {
+        /* Another process may have created the file just now.
+         * Try opening it without O_CREAT and O_EXCL. */
+        fd = open(filename, O_RDWR | O_BINARY);
+        if (fd == -1) {
+          /* Bah! It's hopeless. */
+          int errnum = errno;
+          fprintf(stderr, "profiling: %s: cannot open: %s\n", filename,
+                  strerror(errnum));
+          return;
+        }
       }
     }
   }
Index: compiler-rt/test/profile/Inputs/instrprof-gcov-parallel.driver.c
===================================================================
--- /dev/null
+++ compiler-rt/test/profile/Inputs/instrprof-gcov-parallel.driver.c
@@ -0,0 +1,36 @@
+#include <stdatomic.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define CHILDREN 7
+
+int main(int argc, char *argv[]) {
+  _Atomic int *sync = mmap(NULL, sizeof(int), PROT_READ | PROT_WRITE,
+                           MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+  if (sync == MAP_FAILED)
+    return 1;
+  *sync = 0;
+
+  for (int i = 0; i < CHILDREN; i++) {
+    pid_t pid = fork();
+    if (!pid) {
+      // child
+      while (*sync == 0)
+        ; // wait the parent in order to call execl simultaneously
+      execl(argv[1], argv[1], NULL);
+    } else if (pid == -1) {
+      *sync = 1; // release all children
+      return 1;
+    }
+  }
+
+  // parent
+  *sync = 1; // start the program in all children simultaneously
+  for (int i = 0; i < CHILDREN; i++)
+    wait(NULL);
+
+  return 0;
+}
Index: compiler-rt/test/profile/Inputs/instrprof-gcov-parallel.target.c
===================================================================
--- /dev/null
+++ compiler-rt/test/profile/Inputs/instrprof-gcov-parallel.target.c
@@ -0,0 +1,9 @@
+#define COUNT 101
+
+static volatile int aaa;
+
+int main(int argc, char *argv[]) {
+  for (int i = 0; i < COUNT; i++)
+    aaa++;
+  return 0;
+}
Index: compiler-rt/test/profile/Posix/instrprof-gcov-parallel.test
===================================================================
--- /dev/null
+++ compiler-rt/test/profile/Posix/instrprof-gcov-parallel.test
@@ -0,0 +1,16 @@
+RUN: mkdir -p %t.d
+RUN: cd %t.d
+
+RUN: %clang -o %t.driver %S/../Inputs/instrprof-gcov-parallel.driver.c
+RUN: %clang --coverage -o %t.target %S/../Inputs/instrprof-gcov-parallel.target.c
+RUN: test -f instrprof-gcov-parallel.target.gcno
+
+RUN: rm -f instrprof-gcov-parallel.target.gcda
+RUN: %run %t.driver %t.target
+RUN: llvm-cov gcov instrprof-gcov-parallel.target.gcda
+RUN: FileCheck --input-file instrprof-gcov-parallel.target.c.gcov %s
+
+# Test if the .gcda file is correctly created from one of child processes
+# and counters of all processes are recorded correctly.
+# 707 = CHILDREN * COUNT
+CHECK: 707: {{[0-9]+}}: aaa++;