Thread (42 messages) 42 messages, 6 authors, 2010-02-18

Re: [PATCH 0/3 v4] macvtap driver

From: Ed Swierk <hidden>
Date: 2010-02-09 03:25:10

On Mon, 2010-02-08 at 10:55 -0800, Sridhar Samudrala wrote:
I am also seeing this issue with net-next-2.6.
Basically macvtap_put_user() and macvtap_get_user() call copy_to/from_user
from within a RCU read-side critical section.

The following patch fixes this issue by releasing the RCU read lock before
calling these routines, but instead hold a reference to q->sk.
I've encountered some more problems, with various users of
macvtap_file_get_queue() either calling or neglecting to call
macvtap_file_put_queue() in error cases.

I modified your patch so that when macvtap_file_get_queue() returns 0,
it also calls rcu_read_unlock_bh(), and modified the users
appropriately.

This patch also incorporates my preemption fix for macvlan_count_rx().

Signed-off-by: Ed Swierk <redacted>

---
On Mon, 2010-02-08 at 09:14 -0800, Ed Swierk wrote:
quoted
From: Arnd Bergmann <arnd@arndb.de>
Date: Sat, 30 Jan 2010 23:22:15 +0100
quoted
This is the fourth version of the macvtap driver,
based on the comments I got for the last version
I got a few days ago. Very few changes:

* release netdev in chardev open function so
  we can destroy it properly.
* Implement TUNSETSNDBUF
* fix sleeping call in rcu_read_lock
* Fix comment in namespace isolation patch
* Fix small context difference to make it apply
  to net-next

I can't really test here while travelling, so please
give it a go if you're interested in this driver.
I'm seeing complaints from might_sleep():

Feb  8 16:21:06 ti102 kernel: BUG: sleeping function called from
invalid context at include/linux/kernel.h:155
Feb  8 16:21:06 ti102 kernel: in_atomic(): 1, irqs_disabled(): 0, pid:
2881, name: qemu-kvm
Feb  8 16:21:06 ti102 kernel: Pid: 2881, comm: qemu-kvm Not tainted
2.6.29.6.Ar-224527.2009eswierk8 #1
Feb  8 16:21:06 ti102 kernel: Call Trace:
Feb  8 16:21:06 ti102 kernel: [<c0119250>] __might_sleep+0xdc/0xe3
Feb  8 16:21:06 ti102 kernel: [<c0210f7c>] copy_to_user+0x36/0x106
Feb  8 16:21:06 ti102 kernel: [<c02af568>] memcpy_toiovec+0x2c/0x50
Feb  8 16:21:06 ti102 kernel: [<c02afbb3>] skb_copy_datagram_iovec+0x47/0x184
Feb  8 16:21:06 ti102 kernel: [<c034bd07>] ? _spin_unlock_irqrestore+0x17/0x2c
Feb  8 16:21:06 ti102 kernel: [<f829a776>]
macvtap_aio_read+0x102/0x158 [macvtap]
Feb  8 16:21:06 ti102 kernel: [<c011eaf7>] ? default_wake_function+0x0/0xd
Feb  8 16:21:06 ti102 kernel: [<c016c75f>] do_sync_read+0xab/0xe9
Feb  8 16:21:06 ti102 kernel: [<c0133933>] ? autoremove_wake_function+0x0/0x33
Feb  8 16:21:06 ti102 kernel: [<c019211f>] ? eventfd_read+0x121/0x156
Feb  8 16:21:06 ti102 kernel: [<c011eaf7>] ? default_wake_function+0x0/0xd
Feb  8 16:21:06 ti102 kernel: [<c016d101>] vfs_read+0xb5/0x129
Feb  8 16:21:06 ti102 kernel: [<c016d20e>] sys_read+0x3b/0x60
Feb  8 16:21:06 ti102 kernel: [<c0102e71>] sysenter_do_call+0x12/0x25
I am also seeing this issue with net-next-2.6.
Basically macvtap_put_user() and macvtap_get_user() call copy_to/from_user
from within a RCU read-side critical section.

The following patch fixes this issue by releasing the RCU read lock before
calling these routines, but instead hold a reference to q->sk.

Signed-off-by: Sridhar Samudrala <redacted>

Index: linux-2.6.29.6/drivers/net/macvtap.c
===================================================================
--- linux-2.6.29.6.orig/drivers/net/macvtap.c
+++ linux-2.6.29.6/drivers/net/macvtap.c
@@ -160,8 +160,12 @@ static void macvtap_del_queues(struct ne
 
 static inline struct macvtap_queue *macvtap_file_get_queue(struct file *file)
 {
+	struct macvtap_queue *q;
 	rcu_read_lock_bh();
-	return rcu_dereference(file->private_data);
+	q = rcu_dereference(file->private_data);
+	if (!q)
+		rcu_read_unlock_bh();
+	return q;
 }
 
 static inline void macvtap_file_put_queue(void)
@@ -313,13 +317,14 @@ static unsigned int macvtap_poll(struct 
 	     sock_writeable(&q->sk)))
 		mask |= POLLOUT | POLLWRNORM;
 
-out:
 	macvtap_file_put_queue();
+
+out:
 	return mask;
 }
 
 /* Get packet from user space buffer */
-static ssize_t macvtap_get_user(struct macvtap_queue *q,
+static ssize_t macvtap_get_user(struct macvlan_dev *vlan, struct sock *sk,
 				struct iovec *iv, size_t count,
 				int noblock)
 {
@@ -330,10 +335,10 @@ static ssize_t macvtap_get_user(struct m
 	if (unlikely(len < ETH_HLEN))
 		return -EINVAL;
 
-	skb = sock_alloc_send_skb(&q->sk, NET_IP_ALIGN + len, noblock, &err);
+	skb = sock_alloc_send_skb(sk, NET_IP_ALIGN + len, noblock, &err);
 
 	if (!skb) {
-		macvlan_count_rx(q->vlan, 0, false, false);
+		macvlan_count_rx(vlan, 0, false, false);
 		return err;
 	}
 
@@ -341,14 +346,14 @@ static ssize_t macvtap_get_user(struct m
 	skb_put(skb, count);
 
 	if (skb_copy_datagram_from_iovec(skb, 0, iv, len)) {
-		macvlan_count_rx(q->vlan, 0, false, false);
+		macvlan_count_rx(vlan, 0, false, false);
 		kfree_skb(skb);
 		return -EFAULT;
 	}
 
 	skb_set_network_header(skb, ETH_HLEN);
 
-	macvlan_start_xmit(skb, q->vlan->dev);
+	macvlan_start_xmit(skb, vlan->dev);
 
 	return count;
 }
@@ -359,23 +364,29 @@ static ssize_t macvtap_aio_write(struct 
 	struct file *file = iocb->ki_filp;
 	ssize_t result = -ENOLINK;
 	struct macvtap_queue *q = macvtap_file_get_queue(file);
+	struct macvlan_dev *vlan;
+	struct sock *sk;
 
 	if (!q)
 		goto out;
 
-	result = macvtap_get_user(q, (struct iovec *) iv, iov_length(iv, count),
+	vlan = q->vlan;
+	sk = &q->sk;
+	sock_hold(sk);
+	macvtap_file_put_queue();
+
+	result = macvtap_get_user(vlan, sk, (struct iovec *) iv, iov_length(iv, count),
 			      file->f_flags & O_NONBLOCK);
+	sock_put(sk);
 out:
-	macvtap_file_put_queue();
 	return result;
 }
 
 /* Put packet to the user space buffer */
-static ssize_t macvtap_put_user(struct macvtap_queue *q,
+static ssize_t macvtap_put_user(struct macvlan_dev *vlan,
 				struct sk_buff *skb,
 				struct iovec *iv, int len)
 {
-	struct macvlan_dev *vlan = q->vlan;
 	int ret;
 
 	len = min_t(int, skb->len, len);
@@ -392,15 +403,20 @@ static ssize_t macvtap_aio_read(struct k
 {
 	struct file *file = iocb->ki_filp;
 	struct macvtap_queue *q = macvtap_file_get_queue(file);
+	struct macvlan_dev *vlan;
+	struct sock *sk;
 
 	DECLARE_WAITQUEUE(wait, current);
 	struct sk_buff *skb;
 	ssize_t len, ret = 0;
 
-	if (!q) {
-		ret = -ENOLINK;
-		goto out;
-	}
+	if (!q)
+		return -ENOLINK;
+
+	vlan = q->vlan;
+	sk = &q->sk;
+	sock_hold(sk);
+	macvtap_file_put_queue();
 
 	len = iov_length(iv, count);
 	if (len < 0) {
@@ -408,12 +424,12 @@ static ssize_t macvtap_aio_read(struct k
 		goto out;
 	}
 
-	add_wait_queue(q->sk.sk_sleep, &wait);
+	add_wait_queue(sk->sk_sleep, &wait);
 	while (len) {
 		current->state = TASK_INTERRUPTIBLE;
 
 		/* Read frames from the queue */
-		skb = skb_dequeue(&q->sk.sk_receive_queue);
+		skb = skb_dequeue(&sk->sk_receive_queue);
 		if (!skb) {
 			if (file->f_flags & O_NONBLOCK) {
 				ret = -EAGAIN;
@@ -427,16 +443,16 @@ static ssize_t macvtap_aio_read(struct k
 			schedule();
 			continue;
 		}
-		ret = macvtap_put_user(q, skb, (struct iovec *) iv, len);
+		ret = macvtap_put_user(vlan, skb, (struct iovec *) iv, len);
 		kfree_skb(skb);
 		break;
 	}
 
 	current->state = TASK_RUNNING;
-	remove_wait_queue(q->sk.sk_sleep, &wait);
+	remove_wait_queue(sk->sk_sleep, &wait);
 
 out:
-	macvtap_file_put_queue();
+	sock_put(sk);
 	return ret;
 }
 
Index: linux-2.6.29.6/include/linux/if_macvlan.h
===================================================================
--- linux-2.6.29.6.orig/include/linux/if_macvlan.h
+++ linux-2.6.29.6/include/linux/if_macvlan.h
@@ -42,8 +42,9 @@ static inline void macvlan_count_rx(cons
 				    bool multicast)
 {
 	struct macvlan_rx_stats *rx_stats;
+	int cpu = get_cpu();
 
-	rx_stats = per_cpu_ptr(vlan->rx_stats, smp_processor_id());
+	rx_stats = per_cpu_ptr(vlan->rx_stats, cpu);
 	if (likely(success)) {
 		rx_stats->rx_packets++;;
 		rx_stats->rx_bytes += len;
@@ -52,6 +53,7 @@ static inline void macvlan_count_rx(cons
 	} else {
 		rx_stats->rx_errors++;
 	}
+	put_cpu();
 }
 
 extern int macvlan_common_newlink(struct net_device *dev,

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