io_uring/eventfd: abstract out ev_fd grab + release helpers

In preparation for needing the ev_fd grabbing (and releasing) from
another path, abstract out two helpers for that.

Link: https://lore.kernel.org/r/20240921080307.185186-6-axboe@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/eventfd.c b/io_uring/eventfd.c
index 0946d3da88d36ef8d78bc629fb4cdd2786b9ed4e..d1fdecd0c4582e3d8ef9315581132b588aa8b055 100644 (file)
--- a/io_uring/eventfd.c
+++ b/io_uring/eventfd.c
@@ -47,6 +47,13 @@ static void io_eventfd_put(struct io_ev_fd *ev_fd)
                call_rcu(&ev_fd->rcu, io_eventfd_free);
 }
 
+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.
  */
@@ -74,14 +81,18 @@ static bool io_eventfd_trigger(struct io_ev_fd *ev_fd)
        return false;
 }
 
-void io_eventfd_signal(struct io_ring_ctx *ctx)
+/*
+ * On success, returns with an ev_fd reference grabbed and the RCU read
+ * lock held.
+ */
+static struct io_ev_fd *io_eventfd_grab(struct io_ring_ctx *ctx)
 {
-       struct io_ev_fd *ev_fd = NULL;
+       struct io_ev_fd *ev_fd;
 
        if (READ_ONCE(ctx->rings->cq_flags) & IORING_CQ_EVENTFD_DISABLED)
-               return;
+               return NULL;
 
-       guard(rcu)();
+       rcu_read_lock();
 
        /*
         * rcu_dereference ctx->io_ev_fd once and use it for both for checking
@@ -90,16 +101,24 @@ void io_eventfd_signal(struct io_ring_ctx *ctx)
        ev_fd = rcu_dereference(ctx->io_ev_fd);
 
        /*
-        * Check again if ev_fd exists incase an io_eventfd_unregister call
+        * Check again if ev_fd exists in case an io_eventfd_unregister call
         * completed between the NULL check of ctx->io_ev_fd at the start of
         * the function and rcu_read_lock.
         */
-       if (!io_eventfd_trigger(ev_fd))
-               return;
-       if (!refcount_inc_not_zero(&ev_fd->refs))
-               return;
-       if (__io_eventfd_signal(ev_fd))
-               io_eventfd_put(ev_fd);
+       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)
+{
+       struct io_ev_fd *ev_fd;
+
+       ev_fd = io_eventfd_grab(ctx);
+       if (ev_fd)
+               io_eventfd_release(ev_fd, __io_eventfd_signal(ev_fd));
 }
 
 void io_eventfd_flush_signal(struct io_ring_ctx *ctx)