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Message-ID: <20231207185526.5e59ab53@kernel.org>
Date: Thu, 7 Dec 2023 18:55:26 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Jiri Pirko <jiri@...nulli.us>
Cc: netdev@...r.kernel.org, pabeni@...hat.com, davem@...emloft.net,
edumazet@...gle.com, jacob.e.keller@...el.com, jhs@...atatu.com,
johannes@...solutions.net, andriy.shevchenko@...ux.intel.com,
amritha.nambiar@...el.com, sdf@...gle.com, horms@...nel.org,
przemyslaw.kitszel@...el.com
Subject: Re: [patch net-next v5 5/9] genetlink: introduce per-sock family
private storage
On Wed, 6 Dec 2023 19:21:16 +0100 Jiri Pirko wrote:
> diff --git a/include/net/genetlink.h b/include/net/genetlink.h
> index e18a4c0d69ee..dbf11464e96a 100644
> --- a/include/net/genetlink.h
> +++ b/include/net/genetlink.h
> @@ -87,6 +87,9 @@ struct genl_family {
> int id;
> /* starting number of multicast group IDs in this family */
> unsigned int mcgrp_offset;
> + size_t sock_priv_size;
> + void (*sock_priv_init)(void *priv);
> + void (*sock_priv_destroy)(void *priv);
👍️
but I think it should be above the private fields (and have kdoc)
The families are expected to make use the new fields, and are not
supposed to touch anything private.
> --- a/net/netlink/af_netlink.h
> +++ b/net/netlink/af_netlink.h
> @@ -60,6 +60,21 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
>
> #define nlk_test_bit(nr, sk) test_bit(NETLINK_F_##nr, &nlk_sk(sk)->flags)
>
> +struct genl_sock {
> + struct netlink_sock nlk_sk;
> + struct xarray *family_privs;
> +};
> +
> +static inline struct genl_sock *genl_sk(struct sock *sk)
> +{
> + return container_of(nlk_sk(sk), struct genl_sock, nlk_sk);
> +}
> +
> +/* Size of netlink sock is size of the biggest user with priv,
> + * which is currently just Generic Netlink.
> + */
> +#define NETLINK_SOCK_SIZE sizeof(struct genl_sock)
Would feel a little cleaner to me to add
#define NETLINK_SOCK_PROTO_SIZE 8
add that to the size, build time check that struct genl_sock's
size is <= than sizeof(struct netlink_sock) + NETLINK_SOCK_PROTO_SIZE
This way we don't have to fumble the layering by putting genl stuff
in af_netlink.h
> +struct genl_sk_priv {
> + void (*destructor)(void *priv);
> + long priv[];
> +};
> +
> +static struct genl_sk_priv *genl_sk_priv_alloc(struct genl_family *family)
> +{
> + struct genl_sk_priv *priv;
> +
> + priv = kzalloc(size_add(sizeof(*priv), family->sock_priv_size),
> + GFP_KERNEL);
> + if (!priv)
> + return ERR_PTR(-ENOMEM);
> + priv->destructor = family->sock_priv_destroy;
family->sock_priv_destroy may be in module memory.
I think you need to wipe them when family goes :(
> + if (family->sock_priv_init)
> + family->sock_priv_init(priv->priv);
> + return priv;
> +}
> +static struct xarray *genl_family_privs_get(struct genl_sock *gsk)
> +{
> + struct xarray *family_privs;
> +
> +again:
> + family_privs = READ_ONCE(gsk->family_privs);
> + if (family_privs)
> + return family_privs;
> +
> + family_privs = kzalloc(sizeof(*family_privs), GFP_KERNEL);
> + if (!family_privs)
> + return ERR_PTR(-ENOMEM);
> + xa_init_flags(family_privs, XA_FLAGS_ALLOC);
> +
> + /* Use genl lock to protect family_privs to be
> + * initialized in parallel by different CPU.
> + */
> + genl_lock();
> + if (unlikely(gsk->family_privs)) {
> + xa_destroy(family_privs);
> + kfree(family_privs);
> + genl_unlock();
nit: unlock can be moved up
> + goto again;
why not return READ_ONCE(gsk->family_privs); ?
there's no need to loop
One could also be tempted to:
lock()
if (likely(!gsk->family_privs)) {
WRITE
} else {
destory()
free()
family_privs = READ
}
unlock()
but it could be argued success path should be flat
> + }
> + WRITE_ONCE(gsk->family_privs, family_privs);
> + genl_unlock();
> + return family_privs;
> +}
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