io_uring/napi: fix io_napi_entry RCU accesses

correct 3 RCU structures modifications that were not using the RCU
functions to make their update.

Signed-off-by: Olivier Langlois <[email protected]>
Link: https://lore.kernel.org/r/9f53b5169afa8c7bf3665a0b19dc2f7061173530.1728828877.git.olivier@trillion01.com
Signed-off-by: Jens Axboe <[email protected]>

Author: Olivier Langlois

io_uring/napi.c

@@ -81,19 +81,24 @@ void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock)
 	}
 
 	hlist_add_tail_rcu(&e->node, hash_list);
-	list_add_tail(&e->list, &ctx->napi_list);
+	list_add_tail_rcu(&e->list, &ctx->napi_list);
 	spin_unlock(&ctx->napi_lock);
 }
 
 static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
 {
 	struct io_napi_entry *e;
-	unsigned int i;
 
 	spin_lock(&ctx->napi_lock);
-	hash_for_each(ctx->napi_ht, i, e, node) {
+	/*
+	 * list_for_each_entry_safe() is not required as long as:
+	 * 1. list_del_rcu() does not reset the deleted node next pointer
+	 * 2. kfree_rcu() delays the memory freeing until the next quiescent
+	 *    state
+	 */
+	list_for_each_entry(e, &ctx->napi_list, list) {
 		if (time_after(jiffies, READ_ONCE(e->timeout))) {
-			list_del(&e->list);
+			list_del_rcu(&e->list);
 			hash_del_rcu(&e->node);
 			kfree_rcu(e, rcu);
 		}
@@ -204,13 +209,13 @@ void io_napi_init(struct io_ring_ctx *ctx)
 void io_napi_free(struct io_ring_ctx *ctx)
 {
 	struct io_napi_entry *e;
-	unsigned int i;
 
 	spin_lock(&ctx->napi_lock);
-	hash_for_each(ctx->napi_ht, i, e, node) {
+	list_for_each_entry(e, &ctx->napi_list, list) {
 		hash_del_rcu(&e->node);
 		kfree_rcu(e, rcu);
 	}
+	INIT_LIST_HEAD_RCU(&ctx->napi_list);
 	spin_unlock(&ctx->napi_lock);
 }