netlink: Call cb->done from a worker thread

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>

2 files changed, 25 insertions, 4 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 62bea4591054..602e5ebe9db3 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -322,14 +322,11 @@ static void netlink_skb_set_owner_r(struct sk_buff *skb, struct sock *sk)
         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 sock *sk)
         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
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 3cfd6cc60504..4fdb38318977 100644
--- 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)