io_uring/napi: protect concurrent io_napi_entry timeout accesses

io_napi_entry timeout value can be updated while accessed from the poll
functions.

Its concurrent accesses are wrapped with READ_ONCE()/WRITE_ONCE() macros
to avoid incorrect compiler optimizations.

Signed-off-by: Olivier Langlois <[email protected]>
Link: https://lore.kernel.org/r/3de3087563cf98f75266fd9f85fdba063a8720db.1728828877.git.olivier@trillion01.com
Signed-off-by: Jens Axboe <[email protected]>

Author: Olivier Langlois

io_uring/napi.c

@@ -60,7 +60,7 @@ void __io_napi_add(struct io_ring_ctx *ctx, struct socket *sock)
 	rcu_read_lock();
 	e = io_napi_hash_find(hash_list, napi_id);
 	if (e) {
-		e->timeout = jiffies + NAPI_TIMEOUT;
+		WRITE_ONCE(e->timeout, jiffies + NAPI_TIMEOUT);
 		rcu_read_unlock();
 		return;
 	}
@@ -92,7 +92,7 @@ static void __io_napi_remove_stale(struct io_ring_ctx *ctx)
 
 	spin_lock(&ctx->napi_lock);
 	hash_for_each(ctx->napi_ht, i, e, node) {
-		if (time_after(jiffies, e->timeout)) {
+		if (time_after(jiffies, READ_ONCE(e->timeout))) {
 			list_del(&e->list);
 			hash_del_rcu(&e->node);
 			kfree_rcu(e, rcu);
@@ -150,7 +150,7 @@ static bool __io_napi_do_busy_loop(struct io_ring_ctx *ctx,
 		napi_busy_loop_rcu(e->napi_id, loop_end, loop_end_arg,
 				   ctx->napi_prefer_busy_poll, BUSY_POLL_BUDGET);
 
-		if (time_after(jiffies, e->timeout))
+		if (time_after(jiffies, READ_ONCE(e->timeout)))
 			is_stale = true;
 	}