Avoid a deadlock in forked psx thread exit.
go/captree was seeing lots of libcap_psx_test processes hanging around.
It turns out that the newly added _psx_cleanup() function was deadlocking
because inside a forked processes the psx_tracker.state was _PSX_INFORK
and never _PSX_IDLE.
This completes the fix for:
https://bugzilla.kernel.org/show_bug.cgi?id=215551
Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
diff --git a/psx/psx.c b/psx/psx.c
index 1876978..d9c0485 100644
--- a/psx/psx.c
+++ b/psx/psx.c
@@ -287,7 +287,9 @@
}
/*
- * under lock perform a state transition.
+ * under lock perform a state transition. Changing state is generally
+ * done via this function. However, there is a single exception in
+ * _psx_cleanup().
*/
static void psx_new_state(psx_tracker_state_t was, psx_tracker_state_t is)
{
@@ -351,7 +353,7 @@
*
* We do this because the glibc man page for fork() suggests that
* only a subset of things will work post fork(). Specifically,
- * only a "async-signal-safe functions (see signal- safety(7))
+ * only a "async-signal-safe functions (see signal-safety(7))
* until such time as it calls execve(2)" can be relied upon. That
* man page suggests that you can't expect mutexes to work: "not
* async-signal-safe because it uses pthread_mutex_lock(3)
@@ -733,7 +735,12 @@
* never leave this state since this cleanup is only done at
* program exit.
*/
- psx_new_state(_PSX_IDLE, _PSX_EXITING);
+ psx_lock();
+ while (psx_tracker.state != _PSX_IDLE && psx_tracker.state != _PSX_INFORK) {
+ pthread_cond_wait(&psx_tracker.cond, &psx_tracker.state_mu);
+ }
+ psx_tracker.state = _PSX_EXITING;
+ psx_unlock();
for (ref = psx_tracker.root; ref; ref = next) {
next = ref->next;
