[PATCH 2/3] io_uring/eventfd: clean up rcu locking

[Pavel Begunkov <asml.silence@gmail.com>]

Conditional locking is never welcome if there are better options. Move
rcu locking into io_eventfd_signal(), make it unconditional and use
guards. It also helps with sparse warnings.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 io_uring/eventfd.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/io_uring/eventfd.c b/io_uring/eventfd.c
index a9da2d0d7510..8c2835ac17a0 100644
--- a/io_uring/eventfd.c
+++ b/io_uring/eventfd.c
@@ -47,13 +47,6 @@ static void io_eventfd_do_signal(struct rcu_head *rcu)
 	io_eventfd_put(ev_fd);
 }
 
-static void io_eventfd_release(struct io_ev_fd *ev_fd, bool put_ref)
-{
-	if (put_ref)
-		io_eventfd_put(ev_fd);
-	rcu_read_unlock();
-}
-
 /*
  * Returns true if the caller should put the ev_fd reference, false if not.
  */
@@ -89,11 +82,6 @@ static struct io_ev_fd *io_eventfd_grab(struct io_ring_ctx *ctx)
 {
 	struct io_ev_fd *ev_fd;
 
-	if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
-		return NULL;
-
-	rcu_read_lock();
-
 	/*
 	 * rcu_dereference ctx->io_ev_fd once and use it for both for checking
 	 * and eventfd_signal
@@ -108,15 +96,18 @@ static struct io_ev_fd *io_eventfd_grab(struct io_ring_ctx *ctx)
 	if (io_eventfd_trigger(ev_fd) && refcount_inc_not_zero(&ev_fd->refs))
 		return ev_fd;
 
-	rcu_read_unlock();
 	return NULL;
 }
 
 void io_eventfd_signal(struct io_ring_ctx *ctx, bool cqe_event)
 {
-	bool skip = false, put_ref = true;
+	bool skip = false;
 	struct io_ev_fd *ev_fd;
 
+	if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
+		return;
+
+	guard(rcu)();
 	ev_fd = io_eventfd_grab(ctx);
 	if (!ev_fd)
 		return;
@@ -137,9 +128,8 @@ void io_eventfd_signal(struct io_ring_ctx *ctx, bool cqe_event)
 		spin_unlock(&ctx->completion_lock);
 	}
 
-	if (!skip)
-		put_ref = __io_eventfd_signal(ev_fd);
-	io_eventfd_release(ev_fd, put_ref);
+	if (skip || __io_eventfd_signal(ev_fd))
+		io_eventfd_put(ev_fd);
 }
 
 int io_eventfd_register(struct io_ring_ctx *ctx, void __user *arg,
-- 
2.48.1