[PATCH 1/2] macvtap: rework object lifetime rules
From: Arnd Bergmann
Date: Sat Feb 13 2010 - 05:34:15 EST
The original macvtap code has a number of problems
resulting from the use of RCU for protecting the
access to struct macvtap_queue from open files.
This includes
- need for GFP_ATOMIC allocations for skbs
- potential deadlocks when copy_*_user sleeps
- inability to work with vhost-net
Changing the lifetime of macvtap_queue to always
depend on the open file solves all these. The
RCU reference simply moves one step down to
the reference on the macvlan_dev, which we
only need for nonblocking operations.
Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
---
drivers/net/macvtap.c | 170 +++++++++++++++++++++++++-----------------------
1 files changed, 89 insertions(+), 81 deletions(-)
This patch replaces the previous one that cleans up the locking in a different way.
diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
index ad1f6ef..7050997 100644
--- a/drivers/net/macvtap.c
+++ b/drivers/net/macvtap.c
@@ -60,29 +60,19 @@ static struct cdev macvtap_cdev;
/*
* RCU usage:
- * The macvtap_queue is referenced both from the chardev struct file
- * and from the struct macvlan_dev using rcu_read_lock.
+ * The macvtap_queue and the macvlan_dev are loosely coupled, the
+ * pointers from one to the other can only be read while rcu_read_lock
+ * or macvtap_lock is held.
*
- * We never actually update the contents of a macvtap_queue atomically
- * with RCU but it is used for race-free destruction of a queue when
- * either the file or the macvlan_dev goes away. Pointers back to
- * the dev and the file are implicitly valid as long as the queue
- * exists.
+ * Both the file and the macvlan_dev hold a reference on the macvtap_queue
+ * through sock_hold(&q->sk). When the macvlan_dev goes away first,
+ * q->vlan becomes inaccessible. When the files gets closed,
+ * macvtap_get_queue() fails.
*
- * The callbacks from macvlan are always done with rcu_read_lock held
- * already, while in the file_operations, we get it ourselves.
- *
- * When destroying a queue, we remove the pointers from the file and
- * from the dev and then synchronize_rcu to make sure no thread is
- * still using the queue. There may still be references to the struct
- * sock inside of the queue from outbound SKBs, but these never
- * reference back to the file or the dev. The data structure is freed
- * through __sk_free when both our references and any pending SKBs
- * are gone.
- *
- * macvtap_lock is only used to prevent multiple concurrent open()
- * calls to assign a new vlan->tap pointer. It could be moved into
- * the macvlan_dev itself but is extremely rarely used.
+ * There may still be references to the struct sock inside of the
+ * queue from outbound SKBs, but these never reference back to the
+ * file or the dev. The data structure is freed through __sk_free
+ * when both our references and any pending SKBs are gone.
*/
static DEFINE_SPINLOCK(macvtap_lock);
@@ -100,11 +90,12 @@ static int macvtap_set_queue(struct net_device *dev, struct file *file,
goto out;
err = 0;
- q->vlan = vlan;
+ rcu_assign_pointer(q->vlan, vlan);
rcu_assign_pointer(vlan->tap, q);
+ sock_hold(&q->sk);
q->file = file;
- rcu_assign_pointer(file->private_data, q);
+ file->private_data = q;
out:
spin_unlock(&macvtap_lock);
@@ -112,28 +103,25 @@ out:
}
/*
- * We must destroy each queue exactly once, when either
- * the netdev or the file go away.
+ * The file owning the queue got closed, give up both
+ * the reference that the files holds as well as the
+ * one from the macvlan_dev if that still exists.
*
* Using the spinlock makes sure that we don't get
* to the queue again after destroying it.
- *
- * synchronize_rcu serializes with the packet flow
- * that uses rcu_read_lock.
*/
-static void macvtap_del_queue(struct macvtap_queue **qp)
+static void macvtap_put_queue(struct macvtap_queue *q)
{
- struct macvtap_queue *q;
+ struct macvlan_dev *vlan;
spin_lock(&macvtap_lock);
- q = rcu_dereference(*qp);
- if (!q) {
- spin_unlock(&macvtap_lock);
- return;
+ vlan = rcu_dereference(q->vlan);
+ if (vlan) {
+ rcu_assign_pointer(vlan->tap, NULL);
+ rcu_assign_pointer(q->vlan, NULL);
+ sock_put(&q->sk);
}
- rcu_assign_pointer(q->vlan->tap, NULL);
- rcu_assign_pointer(q->file->private_data, NULL);
spin_unlock(&macvtap_lock);
synchronize_rcu();
@@ -151,21 +139,29 @@ static struct macvtap_queue *macvtap_get_queue(struct net_device *dev,
return rcu_dereference(vlan->tap);
}
+/*
+ * The net_device is going away, give up the reference
+ * that it holds on the queue (all the queues one day)
+ * and safely set the pointer from the queues to NULL.
+ */
static void macvtap_del_queues(struct net_device *dev)
{
struct macvlan_dev *vlan = netdev_priv(dev);
- macvtap_del_queue(&vlan->tap);
-}
+ struct macvtap_queue *q;
-static inline struct macvtap_queue *macvtap_file_get_queue(struct file *file)
-{
- rcu_read_lock_bh();
- return rcu_dereference(file->private_data);
-}
+ spin_lock(&macvtap_lock);
+ q = rcu_dereference(vlan->tap);
+ if (!q) {
+ spin_unlock(&macvtap_lock);
+ return;
+ }
-static inline void macvtap_file_put_queue(void)
-{
- rcu_read_unlock_bh();
+ rcu_assign_pointer(vlan->tap, NULL);
+ rcu_assign_pointer(q->vlan, NULL);
+ spin_unlock(&macvtap_lock);
+
+ synchronize_rcu();
+ sock_put(&q->sk);
}
/*
@@ -275,7 +271,6 @@ static int macvtap_open(struct inode *inode, struct file *file)
q->sock.type = SOCK_RAW;
q->sock.state = SS_CONNECTED;
sock_init_data(&q->sock, &q->sk);
- q->sk.sk_allocation = GFP_ATOMIC; /* for now */
q->sk.sk_write_space = macvtap_sock_write_space;
err = macvtap_set_queue(dev, file, q);
@@ -291,13 +286,14 @@ out:
static int macvtap_release(struct inode *inode, struct file *file)
{
- macvtap_del_queue((struct macvtap_queue **)&file->private_data);
+ struct macvtap_queue *q = file->private_data;
+ macvtap_put_queue(q);
return 0;
}
static unsigned int macvtap_poll(struct file *file, poll_table * wait)
{
- struct macvtap_queue *q = macvtap_file_get_queue(file);
+ struct macvtap_queue *q = file->private_data;
unsigned int mask = POLLERR;
if (!q)
@@ -315,7 +311,6 @@ static unsigned int macvtap_poll(struct file *file, poll_table * wait)
mask |= POLLOUT | POLLWRNORM;
out:
- macvtap_file_put_queue();
return mask;
}
@@ -325,6 +320,7 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q,
int noblock)
{
struct sk_buff *skb;
+ struct macvlan_dev *vlan;
size_t len = count;
int err;
@@ -332,26 +328,37 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q,
return -EINVAL;
skb = sock_alloc_send_skb(&q->sk, NET_IP_ALIGN + len, noblock, &err);
-
- if (!skb) {
- macvlan_count_rx(q->vlan, 0, false, false);
- return err;
- }
+ if (!skb)
+ goto err;
skb_reserve(skb, NET_IP_ALIGN);
skb_put(skb, count);
- if (skb_copy_datagram_from_iovec(skb, 0, iv, 0, len)) {
- macvlan_count_rx(q->vlan, 0, false, false);
- kfree_skb(skb);
- return -EFAULT;
- }
+ err = skb_copy_datagram_from_iovec(skb, 0, iv, 0, len);
+ if (err)
+ goto err;
skb_set_network_header(skb, ETH_HLEN);
-
- macvlan_start_xmit(skb, q->vlan->dev);
+ rcu_read_lock_bh();
+ vlan = rcu_dereference(q->vlan);
+ if (vlan)
+ macvlan_start_xmit(skb, vlan->dev);
+ else
+ kfree_skb(skb);
+ rcu_read_unlock_bh();
return count;
+
+err:
+ rcu_read_lock_bh();
+ vlan = rcu_dereference(q->vlan);
+ if (vlan)
+ macvlan_count_rx(q->vlan, 0, false, false);
+ rcu_read_unlock_bh();
+
+ kfree_skb(skb);
+
+ return err;
}
static ssize_t macvtap_aio_write(struct kiocb *iocb, const struct iovec *iv,
@@ -359,15 +366,10 @@ static ssize_t macvtap_aio_write(struct kiocb *iocb, const struct iovec *iv,
{
struct file *file = iocb->ki_filp;
ssize_t result = -ENOLINK;
- struct macvtap_queue *q = macvtap_file_get_queue(file);
-
- if (!q)
- goto out;
+ struct macvtap_queue *q = file->private_data;
result = macvtap_get_user(q, iv, iov_length(iv, count),
file->f_flags & O_NONBLOCK);
-out:
- macvtap_file_put_queue();
return result;
}
@@ -376,14 +378,17 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
const struct sk_buff *skb,
const struct iovec *iv, int len)
{
- struct macvlan_dev *vlan = q->vlan;
+ struct macvlan_dev *vlan;
int ret;
len = min_t(int, skb->len, len);
ret = skb_copy_datagram_const_iovec(skb, 0, iv, 0, len);
+ rcu_read_lock_bh();
+ vlan = rcu_dereference(q->vlan);
macvlan_count_rx(vlan, len, ret == 0, 0);
+ rcu_read_unlock_bh();
return ret ? ret : len;
}
@@ -392,7 +397,7 @@ static ssize_t macvtap_aio_read(struct kiocb *iocb, const struct iovec *iv,
unsigned long count, loff_t pos)
{
struct file *file = iocb->ki_filp;
- struct macvtap_queue *q = macvtap_file_get_queue(file);
+ struct macvtap_queue *q = file->private_data;
DECLARE_WAITQUEUE(wait, current);
struct sk_buff *skb;
@@ -437,7 +442,6 @@ static ssize_t macvtap_aio_read(struct kiocb *iocb, const struct iovec *iv,
remove_wait_queue(q->sk.sk_sleep, &wait);
out:
- macvtap_file_put_queue();
return ret;
}
@@ -447,12 +451,13 @@ out:
static long macvtap_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
- struct macvtap_queue *q;
+ struct macvtap_queue *q = file->private_data;
+ struct macvlan_dev *vlan;
void __user *argp = (void __user *)arg;
struct ifreq __user *ifr = argp;
unsigned int __user *up = argp;
unsigned int u;
- char devname[IFNAMSIZ];
+ int ret;
switch (cmd) {
case TUNSETIFF:
@@ -464,16 +469,21 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
return 0;
case TUNGETIFF:
- q = macvtap_file_get_queue(file);
- if (!q)
+ rcu_read_lock_bh();
+ vlan = rcu_dereference(q->vlan);
+ if (vlan)
+ dev_hold(vlan->dev);
+ rcu_read_unlock_bh();
+
+ if (!vlan)
return -ENOLINK;
- memcpy(devname, q->vlan->dev->name, sizeof(devname));
- macvtap_file_put_queue();
+ ret = 0;
if (copy_to_user(&ifr->ifr_name, q->vlan->dev->name, IFNAMSIZ) ||
put_user((TUN_TAP_DEV | TUN_NO_PI), &ifr->ifr_flags))
- return -EFAULT;
- return 0;
+ ret = -EFAULT;
+ dev_put(vlan->dev);
+ return ret;
case TUNGETFEATURES:
if (put_user((IFF_TAP | IFF_NO_PI), up))
@@ -484,9 +494,7 @@ static long macvtap_ioctl(struct file *file, unsigned int cmd,
if (get_user(u, up))
return -EFAULT;
- q = macvtap_file_get_queue(file);
q->sk.sk_sndbuf = u;
- macvtap_file_put_queue();
return 0;
case TUNSETOFFLOAD:
--
1.6.3.3
--
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