From: Max Kellermann Date: Fri, 12 Sep 2025 00:06:09 +0000 (+0200) Subject: io_uring/io-wq: fix `max_workers` breakage and `nr_workers` underflow X-Git-Tag: v6.17-rc7~9^2~3 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=cd4ea81be3eb94047ad023c631afd9bd6c295400;p=thirdparty%2Fkernel%2Flinux.git io_uring/io-wq: fix `max_workers` breakage and `nr_workers` underflow 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 new worker") Signed-off-by: Max Kellermann Reviewed-by: Fengnan Chang Signed-off-by: Jens Axboe --- diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index 17dfaa0395c46..1d03b2fc4b259 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; struct io_wq_acct *acct; - bool do_create = false; + bool activated_free_worker, do_create = false; worker = container_of(cb, struct io_worker, create_work); wq = worker->wq; acct = worker->acct; rcu_read_lock(); - do_create = !io_acct_activate_free_worker(acct); + activated_free_worker = io_acct_activate_free_worker(acct); rcu_read_unlock(); - if (!do_create) + if (activated_free_worker) goto no_need_create; raw_spin_lock(&acct->workers_lock);