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[2003:dc:6f31:f700:230:64ff:fe74:809]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45e0157cc84sm22899865e9.7.2025.09.11.17.06.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Sep 2025 17:06:18 -0700 (PDT) From: Max Kellermann To: Jens Axboe , Fengnan Chang , Sasha Levin , Diangang Li , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Max Kellermann , stable@vger.kernel.org Subject: [PATCH] io_uring/io-wq: fix `max_workers` breakage and `nr_workers` underflow Date: Fri, 12 Sep 2025 02:06:09 +0200 Message-ID: <20250912000609.1429966-1-max.kellermann@ionos.com> X-Mailer: git-send-email 2.47.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Commit 88e6c42e40de ("io_uring/io-wq: add check free worker before create new worker") reused the variable `do_create` for something else, abusing it for the free worker check. This caused the value to effectively always be `true` at the time `nr_workers < max_workers` was checked, but it should really be `false`. This means the `max_workers` setting was ignored, and worse: if the limit had already been reached, incrementing `nr_workers` was skipped even though another worker would be created. When later lots of workers exit, the `nr_workers` field could easily underflow, making the problem worse because more and more workers would be created without incrementing `nr_workers`. The simple solution is to use a different variable for the free worker check instead of using one variable for two different things. Cc: stable@vger.kernel.org Fixes: 88e6c42e40de ("io_uring/io-wq: add check free worker before create n= ew worker") Signed-off-by: Max Kellermann Reviewed-by: Fengnan Chang --- io_uring/io-wq.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index 17dfaa0395c4..1d03b2fc4b25 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -352,16 +352,16 @@ static void create_worker_cb(struct callback_head *cb) struct io_wq *wq; =20 struct io_wq_acct *acct; - bool do_create =3D false; + bool activated_free_worker, do_create =3D false; =20 worker =3D container_of(cb, struct io_worker, create_work); wq =3D worker->wq; acct =3D worker->acct; =20 rcu_read_lock(); - do_create =3D !io_acct_activate_free_worker(acct); + activated_free_worker =3D io_acct_activate_free_worker(acct); rcu_read_unlock(); - if (!do_create) + if (activated_free_worker) goto no_need_create; =20 raw_spin_lock(&acct->workers_lock); --=20 2.47.3