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    Subject[PATCH 4.8 17/45] netlink: Call cb->done from a worker thread
    Date
    4.8-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Herbert Xu <herbert@gondor.apana.org.au>


    [ Upstream commit 707693c8a498697aa8db240b93eb76ec62e30892 ]

    The cb->done interface expects to be called in process context.
    This was broken by the netlink RCU conversion. This patch fixes
    it by adding a worker struct to make the cb->done call where
    necessary.

    Fixes: 21e4902aea80 ("netlink: Lockless lookup with RCU grace...")
    Reported-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/netlink/af_netlink.c | 27 +++++++++++++++++++++++----
    net/netlink/af_netlink.h | 2 ++
    2 files changed, 25 insertions(+), 4 deletions(-)

    --- a/net/netlink/af_netlink.c
    +++ b/net/netlink/af_netlink.c
    @@ -322,14 +322,11 @@ static void netlink_skb_set_owner_r(stru
    sk_mem_charge(sk, skb->truesize);
    }

    -static void netlink_sock_destruct(struct sock *sk)
    +static void __netlink_sock_destruct(struct sock *sk)
    {
    struct netlink_sock *nlk = nlk_sk(sk);

    if (nlk->cb_running) {
    - if (nlk->cb.done)
    - nlk->cb.done(&nlk->cb);
    -
    module_put(nlk->cb.module);
    kfree_skb(nlk->cb.skb);
    }
    @@ -346,6 +343,28 @@ static void netlink_sock_destruct(struct
    WARN_ON(nlk_sk(sk)->groups);
    }

    +static void netlink_sock_destruct_work(struct work_struct *work)
    +{
    + struct netlink_sock *nlk = container_of(work, struct netlink_sock,
    + work);
    +
    + nlk->cb.done(&nlk->cb);
    + __netlink_sock_destruct(&nlk->sk);
    +}
    +
    +static void netlink_sock_destruct(struct sock *sk)
    +{
    + struct netlink_sock *nlk = nlk_sk(sk);
    +
    + if (nlk->cb_running && nlk->cb.done) {
    + INIT_WORK(&nlk->work, netlink_sock_destruct_work);
    + schedule_work(&nlk->work);
    + return;
    + }
    +
    + __netlink_sock_destruct(sk);
    +}
    +
    /* This lock without WQ_FLAG_EXCLUSIVE is good on UP and it is _very_ bad on
    * SMP. Look, when several writers sleep and reader wakes them up, all but one
    * immediately hit write lock and grab all the cpus. Exclusive sleep solves
    --- a/net/netlink/af_netlink.h
    +++ b/net/netlink/af_netlink.h
    @@ -3,6 +3,7 @@

    #include <linux/rhashtable.h>
    #include <linux/atomic.h>
    +#include <linux/workqueue.h>
    #include <net/sock.h>

    #define NLGRPSZ(x) (ALIGN(x, sizeof(unsigned long) * 8) / 8)
    @@ -33,6 +34,7 @@ struct netlink_sock {

    struct rhash_head node;
    struct rcu_head rcu;
    + struct work_struct work;
    };

    static inline struct netlink_sock *nlk_sk(struct sock *sk)

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