[PATCH] fix deadlock in synccall after threaded fork

[Samuel Holland <samuel@sholland.org>]

synccall may be called by AS-safe functions such as setuid/setgid after
fork. although fork() resets libc.threads_minus_one, causing synccall to
take the single-threaded path, synccall still takes the thread list
lock. This lock may be held by another thread if for example fork()
races with pthread_create(). After fork(), the value of the lock is
meaningless, so clear it.
---
 src/process/fork.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/process/fork.c b/src/process/fork.c
index 11286ef4..fb42478a 100644
--- a/src/process/fork.c
+++ b/src/process/fork.c
@@ -28,6 +28,7 @@ pid_t fork(void)
 		self->robust_list.off = 0;
 		self->robust_list.pending = 0;
 		self->next = self->prev = self;
+		__thread_list_lock = 0;
 		libc.threads_minus_1 = 0;
 	}
 	__restore_sigs(&set);
-- 
2.21.0