On Tue, Apr 25, 2023 at 11:18:42AM -0700, Stefan Roesch wrote:
> +void __io_napi_add(struct io_ring_ctx *ctx, struct file *file)
> +{
> + unsigned int napi_id;
> + struct socket *sock;
> + struct sock *sk;
> + struct io_napi_ht_entry *he;
> +
> + sock = sock_from_file(file);
> + if (!sock)
> + return;
> +
> + sk = sock->sk;
> + if (!sk)
> + return;
> +
> + napi_id = READ_ONCE(sk->sk_napi_id);
> +
> + /* Non-NAPI IDs can be rejected. */
> + if (napi_id < MIN_NAPI_ID)
> + return;
> +
> + spin_lock(&ctx->napi_lock);
> + hash_for_each_possible(ctx->napi_ht, he, node, napi_id) {
> + if (he->napi_id == napi_id) {
> + he->timeout = jiffies + NAPI_TIMEOUT;
> + goto out;
> + }
> + }
> +
> + he = kmalloc(sizeof(*he), GFP_NOWAIT);
> + if (!he)
> + goto out;
> +
> + he->napi_id = napi_id;
> + he->timeout = jiffies + NAPI_TIMEOUT;
> + hash_add(ctx->napi_ht, &he->node, napi_id);
> +
> + list_add_tail(&he->list, &ctx->napi_list);
> +
> +out:
> + spin_unlock(&ctx->napi_lock);
> +}
What about using GFP_KERNEL to allocate 'he' outside the spin lock, then
kfree() it in the (he->napi_id == napi_id) path after unlock?
That would make the critical section shorter. Also, GFP_NOWAIT is likely
to fail under memory pressure.
--
Ammar Faizi
