[SOLVED] Why does the kernel function:get_next_corpse increase counter after a nf_conn is found?

Issue

I am reading the kernel source code and try to understand the mechanism of ip conntrack. How to understand the function get_next_corpse that increases counter of the nf_conn struct that is found to be cleaned.

static struct nf_conn *
get_next_corpse(struct net *net, int (*iter)(struct nf_conn *i, void *data),
        void *data, unsigned int *bucket)
{
    struct nf_conntrack_tuple_hash *h;
    struct nf_conn *ct;
    struct hlist_nulls_node *n;

    spin_lock_bh(&nf_conntrack_lock);
    for (; *bucket < nf_conntrack_htable_size; (*bucket)++) {
        hlist_nulls_for_each_entry(h, n, &net->ct.hash[*bucket], hnnode) {
            ct = nf_ct_tuplehash_to_ctrack(h);
            if (iter(ct, data))
                goto found;
        }
    }
    hlist_nulls_for_each_entry(h, n, &net->ct.unconfirmed, hnnode) {
        ct = nf_ct_tuplehash_to_ctrack(h);
        if (iter(ct, data))
            set_bit(IPS_DYING_BIT, &ct->status);
    }
    spin_unlock_bh(&nf_conntrack_lock);
    return NULL;
found:
    atomic_inc(&ct->ct_general.use);    //Why ??!
    spin_unlock_bh(&nf_conntrack_lock);
    return ct;
}

As the ct is found to be cleaned, why need atomic_inc(&ct->ct_general.use)?

Solution

Just for keep consistency for that conntrack for concurrency/preemption.

Like the P/V operation introduced by OS textbook.

Answered By - river

Answer Checked By - Clifford M. (WPSolving Volunteer)