From bc369921d6708542eb93da33478762f1162a5805 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Tue, 19 Oct 2021 20:31:26 +0100
Subject: [PATCH] io-wq: max_worker fixes
Git-commit: bc369921d6708542eb93da33478762f1162a5805
Patch-mainline: v5.15-rc7
References: bsc#1205205

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: 2e480058ddc2 ("io-wq: provide a way to limit max number of workers")
Reported-by: Beld Zhang <beldzhang@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/11f90e6b49410b7d1a88f5d04fb8d95bb86b8cf3.1634671835.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Gabriel Krisman Bertazi <krisman@suse.de>
---
 fs/io-wq.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 5bf8aa81715e..422a7ed6a9bd 100644
--- a/fs/io-wq.c
+++ b/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;
-- 
2.35.3