On Fri, Sep 13, 2024 at 10:42:37AM -0700, Stanislav Fomichev wrote:
> On 09/12, Joe Damato wrote:
[...]
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -6493,6 +6493,18 @@ EXPORT_SYMBOL(napi_busy_loop);
> >
> > #endif /* CONFIG_NET_RX_BUSY_POLL */
> >
> > +static void napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
> > +{
> > + spin_lock(&napi_hash_lock);
> > +
> > + napi->napi_id = napi_id;
> > +
> > + hlist_add_head_rcu(&napi->napi_hash_node,
> > + &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
> > +
> > + spin_unlock(&napi_hash_lock);
> > +}
> > +
> > static void napi_hash_add(struct napi_struct *napi)
> > {
> > if (test_bit(NAPI_STATE_NO_BUSY_POLL, &napi->state))
> > @@ -6505,12 +6517,13 @@ static void napi_hash_add(struct napi_struct *napi)
> > if (unlikely(++napi_gen_id < MIN_NAPI_ID))
> > napi_gen_id = MIN_NAPI_ID;
> > } while (napi_by_id(napi_gen_id));
>
> [..]
>
> > - napi->napi_id = napi_gen_id;
> > -
> > - hlist_add_head_rcu(&napi->napi_hash_node,
> > - &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
> >
> > spin_unlock(&napi_hash_lock);
> > +
> > + napi_hash_add_with_id(napi, napi_gen_id);
>
> nit: it is very unlikely that napi_gen_id is gonna wrap around after the
> spin_unlock above, but maybe it's safer to have the following?
>
> static void __napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
> {
> napi->napi_id = napi_id;
> hlist_add_head_rcu(&napi->napi_hash_node,
> &napi_hash[napi->napi_id % HASH_SIZE(napi_hash)]);
> }
>
> static void napi_hash_add_with_id(struct napi_struct *napi, unsigned int napi_id)
> {
> spin_lock(&napi_hash_lock);
> __napi_hash_add_with_id(...);
> spin_unlock(&napi_hash_lock);
> }
>
> And use __napi_hash_add_with_id here before spin_unlock?
After making this change and re-testing on a couple reboots, I haven't
been able to reproduce the page pool issue I mentioned in the other
email [1].
Not sure if I've just been... "getting lucky" or if this fixed
something that I won't fully grasp until I read the mlx5 source
again.
Will test it a few more times, though.
[1]: https://lore.kernel.org/netdev/ZuMC2fYPPtWggB2w@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
