rust: sync: introduce `CondVar`

This is the traditional condition variable or monitor synchronisation
primitive. It is implemented with C's `wait_queue_head_t`.

It allows users to release a lock and go to sleep while guaranteeing
that notifications won't be missed. This is achieved by enqueuing a wait
entry before releasing the lock.

Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Waiman Long <[email protected]>
Reviewed-by: Martin Rodriguez Reboredo <[email protected]>
Signed-off-by: Wedson Almeida Filho <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Miguel Ojeda <[email protected]>

1 files changed, 7 insertions, 0 deletions

diff --git a/rust/helpers.c b/rust/helpers.c
index 2cb7b82053d8..81e80261d597 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -25,6 +25,7 @@
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
 #include <linux/sched/signal.h>
+#include <linux/wait.h>
 
 __noreturn void rust_helper_BUG(void)
 {
@@ -61,6 +62,12 @@ void rust_helper_spin_unlock(spinlock_t *lock)
 }
 EXPORT_SYMBOL_GPL(rust_helper_spin_unlock);
 
+void rust_helper_init_wait(struct wait_queue_entry *wq_entry)
+{
+	init_wait(wq_entry);
+}
+EXPORT_SYMBOL_GPL(rust_helper_init_wait);
+
 int rust_helper_signal_pending(struct task_struct *t)
 {
 	return signal_pending(t);