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/libc/bionic/pthread_atfork.cpp b/libc/bionic/pthread_atfork.cpp
index 2200a6c..84e511c 100644
--- a/libc/bionic/pthread_atfork.cpp
+++ b/libc/bionic/pthread_atfork.cpp
@@ -130,13 +130,15 @@
}
void __bionic_atfork_run_child() {
+ g_atfork_list_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
+
+ pthread_mutex_lock(&g_atfork_list_mutex);
g_atfork_list.walk_forward([](atfork_t* it) {
if (it->child != nullptr) {
it->child();
}
});
-
- g_atfork_list_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
+ pthread_mutex_unlock(&g_atfork_list_mutex);
}
void __bionic_atfork_run_parent() {