Eliminate deadlock in forked child due to delayed resetting mutex lock
For some program implementation, the pattern like below, calling
pthread_atfork to register atfork interfaces.
pthread_atfork(&atfork_prepare, &atfork_parent, &atfork_child);
When the program is expected to reopen the shared library's handle
inherited from parent in child process. Maybe, dlclose is called in
atfork_child to release the shared library handle before reopen it.
Then, dlclose will indrectly call _cxa_finalize and finaly call
__unregister_atfork when dso is not NULL.
atfork_child() -> dlclose() -> __on_dlclose()
-> __cxa_finalize() -> __unregister_atfork(dso)
In __unregister_atfork, firstly, it try to hold the g_atfork_list_mutex
lock to operate the g_atfork_list. Due to the registered atfork_child is
executed before resetting g_atfork_list_mutex lock in child, the child
process will be blocked here because of deadlock.
Test: bionic-unit-tests32 --gtest_filter=pthread.pthread_atfork_child_with_dlclose
without the fixing, the test will be timeout.
Change-Id: I35d3001682c836e0955d6d681bc5f9297fad0c7b
Signed-off-by: Mingwei Shi <mingwei.shi@intel.com>
Signed-off-by: Qiming Shi <qiming.shi@intel.com>
Signed-off-by: Chao Xie <chao.xie@intel.com>
diff --git a/tests/pthread_dlfcn_test.cpp b/tests/pthread_dlfcn_test.cpp
index 64423da..1c733fe 100644
--- a/tests/pthread_dlfcn_test.cpp
+++ b/tests/pthread_dlfcn_test.cpp
@@ -37,6 +37,11 @@
static void AtForkChild3() { g_atfork_child_calls = (g_atfork_child_calls * 10) + 3; }
static void AtForkChild4() { g_atfork_child_calls = (g_atfork_child_calls * 10) + 4; }
+static void* g_atfork_test_handle = nullptr;
+static void AtForkPrepare() {}
+static void AtForkParent() {}
+static void AtForkChild() { dlclose(g_atfork_test_handle); g_atfork_test_handle = dlopen("libtest_pthread_atfork.so", RTLD_NOW | RTLD_LOCAL); }
+
TEST(pthread, pthread_atfork_with_dlclose) {
ASSERT_EQ(0, pthread_atfork(AtForkPrepare1, AtForkParent1, AtForkChild1));
@@ -82,3 +87,28 @@
AssertChildExited(pid, 0);
}
+
+TEST(pthread, pthread_atfork_child_with_dlclose) {
+
+ g_atfork_test_handle = dlopen("libtest_pthread_atfork.so", RTLD_NOW | RTLD_LOCAL);
+ ASSERT_TRUE(g_atfork_test_handle != nullptr) << dlerror();
+ typedef int (*fn_t)(void (*)(void), void (*)(void), void (*)(void));
+ fn_t fn = reinterpret_cast<fn_t>(dlsym(g_atfork_test_handle, "proxy_pthread_atfork"));
+ ASSERT_TRUE(fn != nullptr) << dlerror();
+ // the library registers 2 additional atfork handlers in a constructor
+
+ ASSERT_EQ(0, pthread_atfork(AtForkPrepare, AtForkParent, AtForkChild));
+
+ pid_t pid = fork();
+
+ ASSERT_NE(-1, pid) << strerror(errno);
+
+ if (pid == 0) {
+ _exit(0);
+ }
+
+ AssertChildExited(pid, 0);
+
+ EXPECT_EQ(0, dlclose(g_atfork_test_handle));
+ g_atfork_test_handle = nullptr;
+}