[OpenMP] Fix race condition in omp_init_lock

This is a partial fix for bug 34050.

This prevents callers of omp_set_lock (which does not hold __kmp_global_lock)
from ever seeing an uninitialized version of __kmp_i_lock_table.table.

It does not solve a use-after-free race condition if omp_set_lock obtains a
pointer to __kmp_i_lock_table.table before it is updated and then attempts to
dereference afterwards. That race is far less likely and can be handled in a
separate patch.

The unit test usually segfaults on the current trunk revision. It passes with
the patch.

Patch by Adam Azarchs

Differential Revision: https://reviews.llvm.org/D39439

llvm-svn: 317115

1 files changed, 4 insertions, 3 deletions

diff --git a/openmp/runtime/src/kmp_lock.cpp b/openmp/runtime/src/kmp_lock.cpp
index bb18a6d196e..9c7dcaff74a 100644
--- a/openmp/runtime/src/kmp_lock.cpp
+++ b/openmp/runtime/src/kmp_lock.cpp
@@ -3058,11 +3058,12 @@ kmp_indirect_lock_t *__kmp_allocate_indirect_lock(void **user_lock,
     if (idx == __kmp_i_lock_table.size) {
       // Double up the space for block pointers
       int row = __kmp_i_lock_table.size / KMP_I_LOCK_CHUNK;
-      kmp_indirect_lock_t **old_table = __kmp_i_lock_table.table;
-      __kmp_i_lock_table.table = (kmp_indirect_lock_t **)__kmp_allocate(
+      kmp_indirect_lock_t **new_table = (kmp_indirect_lock_t **)__kmp_allocate(
           2 * row * sizeof(kmp_indirect_lock_t *));
-      KMP_MEMCPY(__kmp_i_lock_table.table, old_table,
+      KMP_MEMCPY(new_table, __kmp_i_lock_table.table,
                  row * sizeof(kmp_indirect_lock_t *));
+      kmp_indirect_lock_t **old_table = __kmp_i_lock_table.table;
+      __kmp_i_lock_table.table = new_table;
       __kmp_free(old_table);
       // Allocate new objects in the new blocks
       for (int i = row; i < 2 * row; ++i)