io_uring/rsrc: kill rsrc_ref_lock

We use ->rsrc_ref_lock spinlock to protect ->rsrc_ref_list in
io_rsrc_node_ref_zero(). Now we removed pcpu refcounting, which means
io_rsrc_node_ref_zero() is not executed from the irq context as an RCU
callback anymore, and we also put it under ->uring_lock.
io_rsrc_node_switch(), which queues up nodes into the list, is also
protected by ->uring_lock, so we can safely get rid of ->rsrc_ref_lock.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/6b60af883c263551190b526a55ff2c9d5ae07141.1680576071.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/io_uring_types.h

@@ -333,8 +333,8 @@ struct io_ring_ctx {
 	struct delayed_work		rsrc_put_work;
 	struct callback_head		rsrc_put_tw;
 	struct llist_head		rsrc_put_llist;
+	/* protected by ->uring_lock */
 	struct list_head		rsrc_ref_list;
-	spinlock_t			rsrc_ref_lock;
 
 	struct list_head		io_buffers_pages;
 

io_uring/io_uring.c

@@ -325,7 +325,6 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	INIT_LIST_HEAD(&ctx->defer_list);
 	INIT_LIST_HEAD(&ctx->timeout_list);
 	INIT_LIST_HEAD(&ctx->ltimeout_list);
-	spin_lock_init(&ctx->rsrc_ref_lock);
 	INIT_LIST_HEAD(&ctx->rsrc_ref_list);
 	INIT_DELAYED_WORK(&ctx->rsrc_put_work, io_rsrc_put_work);
 	init_task_work(&ctx->rsrc_put_tw, io_rsrc_put_tw);

io_uring/rsrc.c

@@ -209,11 +209,9 @@ void io_rsrc_node_ref_zero(struct io_rsrc_node *node)
 	__must_hold(&node->rsrc_data->ctx->uring_lock)
 {
 	struct io_ring_ctx *ctx = node->rsrc_data->ctx;
-	unsigned long flags;
 	bool first_add = false;
 	unsigned long delay = HZ;
 
-	spin_lock_irqsave(&ctx->rsrc_ref_lock, flags);
 	node->done = true;
 
 	/* if we are mid-quiesce then do not delay */
@@ -229,7 +227,6 @@ void io_rsrc_node_ref_zero(struct io_rsrc_node *node)
 		list_del(&node->node);
 		first_add |= llist_add(&node->llist, &ctx->rsrc_put_llist);
 	}
-	spin_unlock_irqrestore(&ctx->rsrc_ref_lock, flags);
 
 	if (!first_add)
 		return;
@@ -268,9 +265,7 @@ void io_rsrc_node_switch(struct io_ring_ctx *ctx,
 		struct io_rsrc_node *rsrc_node = ctx->rsrc_node;
 
 		rsrc_node->rsrc_data = data_to_kill;
-		spin_lock_irq(&ctx->rsrc_ref_lock);
 		list_add_tail(&rsrc_node->node, &ctx->rsrc_ref_list);
-		spin_unlock_irq(&ctx->rsrc_ref_lock);
 
 		atomic_inc(&data_to_kill->refs);
 		/* put master ref */