coroutine-lock: qemu_co_queue_restart_all is a coroutine-only qemu_co_enter_all

qemu_co_queue_restart_all is basically the same as qemu_co_enter_all
but without a QemuLockable argument.  That's perfectly fine, but only as
long as the function is marked coroutine_fn.  If used outside coroutine
context, qemu_co_queue_wait will attempt to take the lock and that
is just broken: if you are calling qemu_co_queue_restart_all outside
coroutine context, the lock is going to be a QemuMutex which cannot be
taken twice by the same thread.

The patch adds the marker to qemu_co_queue_restart_all and to its sole
non-coroutine_fn caller; it then reimplements the function in terms of
qemu_co_enter_all_impl, to remove duplicated code and to clarify that the
latter also works in coroutine context.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-Id: <20220427130830.150180-4-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/include/qemu/coroutine.h b/include/qemu/coroutine.h
index e5954635f6..43df7a7e66 100644
--- a/include/qemu/coroutine.h
+++ b/include/qemu/coroutine.h
@@ -216,10 +216,11 @@ void coroutine_fn qemu_co_queue_wait_impl(CoQueue *queue, QemuLockable *lock);
 bool coroutine_fn qemu_co_queue_next(CoQueue *queue);
 
 /**
- * Empties the CoQueue; all coroutines are woken up.
- * OK to run from coroutine and non-coroutine context.
+ * Empties the CoQueue and queues the coroutine to run after
+ * the currently-running coroutine yields.
+ * Used from coroutine context, use qemu_co_enter_all outside.
  */
-void qemu_co_queue_restart_all(CoQueue *queue);
+void coroutine_fn qemu_co_queue_restart_all(CoQueue *queue);
 
 /**
  * Removes the next coroutine from the CoQueue, and wake it up.  Unlike