To avoid race issues, pthread::once() uses pthread_mutex. This caused the handle leak which was fixed by the commit 2c5433e5da82. However, this fix introduced another race issue, i.e., the mutex may be used after it is destroyed. With this patch, do not use pthread_mutex in pthread::once() to avoid both issues. Instead, InterlockedExchage() is used.
Addresses: https://cygwin.com/pipermail/cygwin/2024-May/255987.html Reported-by: Bruno Haible <br...@clisp.org> Fixes: 2c5433e5da82 ("Cygwin: pthread: Fix handle leak in pthread_once.") Reviewed-by: Signed-off-by: Takashi Yano <takashi.y...@nifty.ne.jp> --- winsup/cygwin/thread.cc | 25 ++++--------------------- 1 file changed, 4 insertions(+), 21 deletions(-) diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc index 0f8327831..1e5f9362b 100644 --- a/winsup/cygwin/thread.cc +++ b/winsup/cygwin/thread.cc @@ -2045,27 +2045,10 @@ pthread::create (pthread_t *thread, const pthread_attr_t *attr, int pthread::once (pthread_once_t *once_control, void (*init_routine) (void)) { - // already done ? - if (once_control->state) - return 0; - - pthread_mutex_lock (&once_control->mutex); - /* Here we must set a cancellation handler to unlock the mutex if needed */ - /* but a cancellation handler is not the right thing. We need this in the thread - *cleanup routine. Assumption: a thread can only be in one pthread_once routine - *at a time. Stote a mutex_t *in the pthread_structure. if that's non null unlock - *on pthread_exit (); - */ - if (!once_control->state) - { - init_routine (); - once_control->state = 1; - pthread_mutex_unlock (&once_control->mutex); - while (pthread_mutex_destroy (&once_control->mutex) == EBUSY); - return 0; - } - /* Here we must remove our cancellation handler */ - pthread_mutex_unlock (&once_control->mutex); + /* The type of &once_control->state is int *, which is compatible with + LONG * (the type of the first argument of InterlockedExchange()). */ + if (!InterlockedExchange (&once_control->state, 1)) + init_routine (); return 0; } -- 2.45.1
