Re: [PATCH 5.15] io-wq: max_worker fixes

[Pavel Begunkov <asml.silence@gmail.com>]

On 10/19/21 20:31, Pavel Begunkov wrote:
> 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().

Jens, can you add

Reported-by: Beld Zhang <beldzhang@gmail.com>

> 
> Fixes: 2e480058ddc2 ("io-wq: provide a way to limit max number of workers")
> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> ---
>   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 811299ac9684..cdf1719f6be6 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;
>   	}
> @@ -1290,15 +1290,18 @@ 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;
> 

-- 
Pavel Begunkov