netlink: don't hold mutex in rcu callback when releasing mmapd ring

Kirill A. Shutemov says:

This simple test-case trigers few locking asserts in kernel:

int main(int argc, char **argv)
{
        unsigned int block_size = 16 * 4096;
        struct nl_mmap_req req = {
                .nm_block_size          = block_size,
                .nm_block_nr            = 64,
                .nm_frame_size          = 16384,
                .nm_frame_nr            = 64 * block_size / 16384,
        };
        unsigned int ring_size;
	int fd;

	fd = socket(AF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
        if (setsockopt(fd, SOL_NETLINK, NETLINK_RX_RING, &req, sizeof(req)) < 0)
                exit(1);
        if (setsockopt(fd, SOL_NETLINK, NETLINK_TX_RING, &req, sizeof(req)) < 0)
                exit(1);

	ring_size = req.nm_block_nr * req.nm_block_size;
	mmap(NULL, 2 * ring_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
	return 0;
}

+++ exited with 0 +++
BUG: sleeping function called from invalid context at /home/kas/git/public/linux-mm/kernel/locking/mutex.c:616
in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: init
3 locks held by init/1:
 #0:  (reboot_mutex){+.+...}, at: [<ffffffff81080959>] SyS_reboot+0xa9/0x220
 #1:  ((reboot_notifier_list).rwsem){.+.+..}, at: [<ffffffff8107f379>] __blocking_notifier_call_chain+0x39/0x70
 #2:  (rcu_callback){......}, at: [<ffffffff810d32e0>] rcu_do_batch.isra.49+0x160/0x10c0
Preemption disabled at:[<ffffffff8145365f>] __delay+0xf/0x20

CPU: 1 PID: 1 Comm: init Not tainted 4.1.0-00009-gbddf4c4818e0 #253
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS Debian-1.8.2-1 04/01/2014
 ffff88017b3d8000 ffff88027bc03c38 ffffffff81929ceb 0000000000000102
 0000000000000000 ffff88027bc03c68 ffffffff81085a9d 0000000000000002
 ffffffff81ca2a20 0000000000000268 0000000000000000 ffff88027bc03c98
Call Trace:
 <IRQ>  [<ffffffff81929ceb>] dump_stack+0x4f/0x7b
 [<ffffffff81085a9d>] ___might_sleep+0x16d/0x270
 [<ffffffff81085bed>] __might_sleep+0x4d/0x90
 [<ffffffff8192e96f>] mutex_lock_nested+0x2f/0x430
 [<ffffffff81932fed>] ? _raw_spin_unlock_irqrestore+0x5d/0x80
 [<ffffffff81464143>] ? __this_cpu_preempt_check+0x13/0x20
 [<ffffffff8182fc3d>] netlink_set_ring+0x1ed/0x350
 [<ffffffff8182e000>] ? netlink_undo_bind+0x70/0x70
 [<ffffffff8182fe20>] netlink_sock_destruct+0x80/0x150
 [<ffffffff817e484d>] __sk_free+0x1d/0x160
 [<ffffffff817e49a9>] sk_free+0x19/0x20
[..]

Cong Wang says:

We can't hold mutex lock in a rcu callback, [..]

Thomas Graf says:

The socket should be dead at this point. It might be simpler to
add a netlink_release_ring() function which doesn't require
locking at all.

Reported-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Diagnosed-by: Cong Wang <cwang@twopensource.com>
Suggested-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 47 insertions, 32 deletions

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 9a0ae7172f92..d8e2e3918ce2 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -357,25 +357,52 @@ err1:
         return NULL;
 }
 
+
+static void
+__netlink_set_ring(struct sock *sk, struct nl_mmap_req *req, bool tx_ring, void **pg_vec,
+                   unsigned int order)
+{
+        struct netlink_sock *nlk = nlk_sk(sk);
+        struct sk_buff_head *queue;
+        struct netlink_ring *ring;
+
+        queue = tx_ring ? &sk->sk_write_queue : &sk->sk_receive_queue;
+        ring  = tx_ring ? &nlk->tx_ring : &nlk->rx_ring;
+
+        spin_lock_bh(&queue->lock);
+
+        ring->frame_max         = req->nm_frame_nr - 1;
+        ring->head              = 0;
+        ring->frame_size        = req->nm_frame_size;
+        ring->pg_vec_pages      = req->nm_block_size / PAGE_SIZE;
+
+        swap(ring->pg_vec_len, req->nm_block_nr);
+        swap(ring->pg_vec_order, order);
+        swap(ring->pg_vec, pg_vec);
+
+        __skb_queue_purge(queue);
+        spin_unlock_bh(&queue->lock);
+
+        WARN_ON(atomic_read(&nlk->mapped));
+
+        if (pg_vec)
+                free_pg_vec(pg_vec, order, req->nm_block_nr);
+}
+
 static int netlink_set_ring(struct sock *sk, struct nl_mmap_req *req,
-                            bool closing, bool tx_ring)
+                            bool tx_ring)
 {
         struct netlink_sock *nlk = nlk_sk(sk);
         struct netlink_ring *ring;
-        struct sk_buff_head *queue;
         void **pg_vec = NULL;
         unsigned int order = 0;
-        int err;
 
         ring  = tx_ring ? &nlk->tx_ring : &nlk->rx_ring;
-        queue = tx_ring ? &sk->sk_write_queue : &sk->sk_receive_queue;
 
-        if (!closing) {
-                if (atomic_read(&nlk->mapped))
-                        return -EBUSY;
-                if (atomic_read(&ring->pending))
-                        return -EBUSY;
-        }
+        if (atomic_read(&nlk->mapped))
+                return -EBUSY;
+        if (atomic_read(&ring->pending))
+                return -EBUSY;
 
         if (req->nm_block_nr) {
                 if (ring->pg_vec != NULL)
@@ -407,31 +434,19 @@ static int netlink_set_ring(struct sock *sk, struct nl_mmap_req *req,
                         return -EINVAL;
         }
 
-        err = -EBUSY;
         mutex_lock(&nlk->pg_vec_lock);
-        if (closing || atomic_read(&nlk->mapped) == 0) {
-                err = 0;
-                spin_lock_bh(&queue->lock);
-
-                ring->frame_max         = req->nm_frame_nr - 1;
-                ring->head              = 0;
-                ring->frame_size        = req->nm_frame_size;
-                ring->pg_vec_pages      = req->nm_block_size / PAGE_SIZE;
-
-                swap(ring->pg_vec_len, req->nm_block_nr);
-                swap(ring->pg_vec_order, order);
-                swap(ring->pg_vec, pg_vec);
-
-                __skb_queue_purge(queue);
-                spin_unlock_bh(&queue->lock);
-
-                WARN_ON(atomic_read(&nlk->mapped));
+        if (atomic_read(&nlk->mapped) == 0) {
+                __netlink_set_ring(sk, req, tx_ring, pg_vec, order);
+                mutex_unlock(&nlk->pg_vec_lock);
+                return 0;
         }
+
         mutex_unlock(&nlk->pg_vec_lock);
 
         if (pg_vec)
                 free_pg_vec(pg_vec, order, req->nm_block_nr);
-        return err;
+
+        return -EBUSY;
 }
 
 static void netlink_mm_open(struct vm_area_struct *vma)
@@ -900,10 +915,10 @@ static void netlink_sock_destruct(struct sock *sk)
 
                 memset(&req, 0, sizeof(req));
                 if (nlk->rx_ring.pg_vec)
-                        netlink_set_ring(sk, &req, true, false);
+                        __netlink_set_ring(sk, &req, false, NULL, 0);
                 memset(&req, 0, sizeof(req));
                 if (nlk->tx_ring.pg_vec)
-                        netlink_set_ring(sk, &req, true, true);
+                        __netlink_set_ring(sk, &req, true, NULL, 0);
         }
 #endif /* CONFIG_NETLINK_MMAP */
 
@@ -2223,7 +2238,7 @@ static int netlink_setsockopt(struct socket *sock, int level, int optname,
                         return -EINVAL;
                 if (copy_from_user(&req, optval, sizeof(req)))
                         return -EFAULT;
-                err = netlink_set_ring(sk, &req, false,
+                err = netlink_set_ring(sk, &req,
                                        optname == NETLINK_TX_RING);
                 break;
         }