io-wq: max_worker fixes

First, fix nr_workers checks against max_workers, with max_worker
registration, it may pretty easily happen that nr_workers > max_workers.

Also, synchronise writing to acct->max_worker with wqe->lock. It's not
an actual problem, but as we don't care about io_wqe_create_worker(),
it's better than WRITE_ONCE()/READ_ONCE().

Fixes: 2e48005 ("io-wq: provide a way to limit max number of workers")
Reported-by: Beld Zhang <[email protected]>
Signed-off-by: Pavel Begunkov <[email protected]>
Link: https://lore.kernel.org/r/11f90e6b49410b7d1a88f5d04fb8d95bb86b8cf3.1634671835.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <[email protected]>

Author: isilence

fs/io-wq.c

@@ -253,7 +253,7 @@ static bool io_wqe_create_worker(struct io_wqe *wqe, struct io_wqe_acct *acct)
 		pr_warn_once("io-wq is not configured for unbound workers");
 
 	raw_spin_lock(&wqe->lock);
-	if (acct->nr_workers == acct->max_workers) {
+	if (acct->nr_workers >= acct->max_workers) {
 		raw_spin_unlock(&wqe->lock);
 		return true;
 	}
@@ -1291,15 +1291,18 @@ int io_wq_max_workers(struct io_wq *wq, int *new_count)
 
 	rcu_read_lock();
 	for_each_node(node) {
+		struct io_wqe *wqe = wq->wqes[node];
 		struct io_wqe_acct *acct;
 
+		raw_spin_lock(&wqe->lock);
 		for (i = 0; i < IO_WQ_ACCT_NR; i++) {
-			acct = &wq->wqes[node]->acct[i];
+			acct = &wqe->acct[i];
 			prev = max_t(int, acct->max_workers, prev);
 			if (new_count[i])
 				acct->max_workers = new_count[i];
 			new_count[i] = prev;
 		}
+		raw_spin_unlock(&wqe->lock);
 	}
 	rcu_read_unlock();
 	return 0;