Commit cd4ea81b authored by Max Kellermann's avatar Max Kellermann Committed by Jens Axboe
Browse files

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: default avatarMax Kellermann <max.kellermann@ionos.com>
Reviewed-by: default avatarFengnan Chang <changfengnan@bytedance.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 98b6fa62

io_uring/io-wq.c

+3 −3
Original line number Diff line number Diff line
@@ -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);