[PATCH 0/4] vhost private_data rcu removal

[PATCH 0/4] vhost private_data rcu removal

[Asias He]

Asias He (4):
  vhost-net: Always access vq->private_data under vq mutex
  vhost-test: Always access vq->private_data under vq mutex
  vhost-scsi: Always access vq->private_data under vq mutex
  vhost: Remove custom vhost rcu usage

 drivers/vhost/net.c   | 37 ++++++++++++++++---------------------
 drivers/vhost/scsi.c  | 17 ++++++-----------
 drivers/vhost/test.c  | 20 +++++++++-----------
 drivers/vhost/vhost.h | 10 ++--------
 4 files changed, 33 insertions(+), 51 deletions(-)

-- 
1.8.1.4

[PATCH 1/4] vhost-net: Always access vq->private_data under vq mutex

[Asias He]

Signed-off-by: Asias He <asias@redhat.com>
---
 drivers/vhost/net.c | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 2b51e23..b616d9a 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -349,12 +349,11 @@ static void handle_tx(struct vhost_net *net)
 	struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
 	bool zcopy, zcopy_used;
 
-	/* TODO: check that we are running from vhost_worker? */
-	sock = rcu_dereference_check(vq->private_data, 1);
+	mutex_lock(&vq->mutex);
+	sock = vq->private_data;
 	if (!sock)
-		return;
+		goto out;
 
-	mutex_lock(&vq->mutex);
 	vhost_disable_notify(&net->dev, vq);
 
 	hdr_size = nvq->vhost_hlen;
@@ -463,7 +462,7 @@ static void handle_tx(struct vhost_net *net)
 			break;
 		}
 	}
-
+out:
 	mutex_unlock(&vq->mutex);
 }
 
@@ -572,14 +571,14 @@ static void handle_rx(struct vhost_net *net)
 	s16 headcount;
 	size_t vhost_hlen, sock_hlen;
 	size_t vhost_len, sock_len;
-	/* TODO: check that we are running from vhost_worker? */
-	struct socket *sock = rcu_dereference_check(vq->private_data, 1);
-
-	if (!sock)
-		return;
+	struct socket *sock;
 
 	mutex_lock(&vq->mutex);
+	sock = vq->private_data;
+	if (!sock)
+		goto out;
 	vhost_disable_notify(&net->dev, vq);
+
 	vhost_hlen = nvq->vhost_hlen;
 	sock_hlen = nvq->sock_hlen;
 
@@ -654,7 +653,7 @@ static void handle_rx(struct vhost_net *net)
 			break;
 		}
 	}
-
+out:
 	mutex_unlock(&vq->mutex);
 }
 
-- 
1.8.1.4

[PATCH 2/4] vhost-test: Always access vq->private_data under vq mutex

[Asias He]

Signed-off-by: Asias He <asias@redhat.com>
---
 drivers/vhost/test.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index dc526eb..435b911 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -48,11 +48,12 @@ static void handle_vq(struct vhost_test *n)
 	size_t len, total_len = 0;
 	void *private;
 
-	private = rcu_dereference_check(vq->private_data, 1);
-	if (!private)
-		return;
 
 	mutex_lock(&vq->mutex);
+	private = vq->private_data;
+	if (!private)
+		goto out;
+
 	vhost_disable_notify(&n->dev, vq);
 
 	for (;;) {
@@ -89,7 +90,7 @@ static void handle_vq(struct vhost_test *n)
 			break;
 		}
 	}
-
+out:
 	mutex_unlock(&vq->mutex);
 }
 
-- 
1.8.1.4

[PATCH 3/4] vhost-scsi: Always access vq->private_data under vq mutex

[Asias He]

Signed-off-by: Asias He <asias@redhat.com>
---
 drivers/vhost/scsi.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 5531ebc..d78768b 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -896,19 +896,15 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 	int head, ret;
 	u8 target;
 
+	mutex_lock(&vq->mutex);
 	/*
 	 * We can handle the vq only after the endpoint is setup by calling the
 	 * VHOST_SCSI_SET_ENDPOINT ioctl.
-	 *
-	 * TODO: Check that we are running from vhost_worker which acts
-	 * as read-side critical section for vhost kind of RCU.
-	 * See the comments in struct vhost_virtqueue in drivers/vhost/vhost.h
 	 */
-	vs_tpg = rcu_dereference_check(vq->private_data, 1);
+	vs_tpg = vq->private_data;
 	if (!vs_tpg)
-		return;
+		goto out;
 
-	mutex_lock(&vq->mutex);
 	vhost_disable_notify(&vs->dev, vq);
 
 	for (;;) {
@@ -1058,6 +1054,7 @@ err_free:
 	vhost_scsi_free_cmd(cmd);
 err_cmd:
 	vhost_scsi_send_bad_target(vs, vq, head, out);
+out:
 	mutex_unlock(&vq->mutex);
 }
 
-- 
1.8.1.4

[PATCH 4/4] vhost: Remove custom vhost rcu usage

[Asias He]

Now, vq->private_data is always accessed under vq mutex. No need to play
the vhost rcu trick.

Signed-off-by: Asias He <asias@redhat.com>
---
 drivers/vhost/net.c   | 16 ++++++----------
 drivers/vhost/scsi.c  |  6 ++----
 drivers/vhost/test.c  | 11 ++++-------
 drivers/vhost/vhost.h | 10 ++--------
 4 files changed, 14 insertions(+), 29 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index b616d9a..05bdc3c 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -15,7 +15,6 @@
 #include <linux/moduleparam.h>
 #include <linux/mutex.h>
 #include <linux/workqueue.h>
-#include <linux/rcupdate.h>
 #include <linux/file.h>
 #include <linux/slab.h>
 
@@ -751,8 +750,7 @@ static int vhost_net_enable_vq(struct vhost_net *n,
 	struct vhost_poll *poll = n->poll + (nvq - n->vqs);
 	struct socket *sock;
 
-	sock = rcu_dereference_protected(vq->private_data,
-					 lockdep_is_held(&vq->mutex));
+	sock = vq->private_data;
 	if (!sock)
 		return 0;
 
@@ -765,10 +763,9 @@ static struct socket *vhost_net_stop_vq(struct vhost_net *n,
 	struct socket *sock;
 
 	mutex_lock(&vq->mutex);
-	sock = rcu_dereference_protected(vq->private_data,
-					 lockdep_is_held(&vq->mutex));
+	sock = vq->private_data;
 	vhost_net_disable_vq(n, vq);
-	rcu_assign_pointer(vq->private_data, NULL);
+	vq->private_data = NULL;
 	mutex_unlock(&vq->mutex);
 	return sock;
 }
@@ -924,8 +921,7 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 	}
 
 	/* start polling new socket */
-	oldsock = rcu_dereference_protected(vq->private_data,
-					    lockdep_is_held(&vq->mutex));
+	oldsock = vq->private_data;
 	if (sock != oldsock) {
 		ubufs = vhost_net_ubuf_alloc(vq,
 					     sock && vhost_sock_zcopy(sock));
@@ -935,7 +931,7 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 		}
 
 		vhost_net_disable_vq(n, vq);
-		rcu_assign_pointer(vq->private_data, sock);
+		vq->private_data = sock;
 		r = vhost_init_used(vq);
 		if (r)
 			goto err_used;
@@ -969,7 +965,7 @@ static long vhost_net_set_backend(struct vhost_net *n, unsigned index, int fd)
 	return 0;
 
 err_used:
-	rcu_assign_pointer(vq->private_data, oldsock);
+	vq->private_data = oldsock;
 	vhost_net_enable_vq(n, vq);
 	if (ubufs)
 		vhost_net_ubuf_put_and_wait(ubufs);
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index d78768b..de6d817 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1223,9 +1223,8 @@ vhost_scsi_set_endpoint(struct vhost_scsi *vs,
 		       sizeof(vs->vs_vhost_wwpn));
 		for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
 			vq = &vs->vqs[i].vq;
-			/* Flushing the vhost_work acts as synchronize_rcu */
 			mutex_lock(&vq->mutex);
-			rcu_assign_pointer(vq->private_data, vs_tpg);
+			vq->private_data = vs_tpg;
 			vhost_init_used(vq);
 			mutex_unlock(&vq->mutex);
 		}
@@ -1304,9 +1303,8 @@ vhost_scsi_clear_endpoint(struct vhost_scsi *vs,
 	if (match) {
 		for (i = 0; i < VHOST_SCSI_MAX_VQ; i++) {
 			vq = &vs->vqs[i].vq;
-			/* Flushing the vhost_work acts as synchronize_rcu */
 			mutex_lock(&vq->mutex);
-			rcu_assign_pointer(vq->private_data, NULL);
+			vq->private_data = NULL;
 			mutex_unlock(&vq->mutex);
 		}
 	}
diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index 435b911..5f23477 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -13,7 +13,6 @@
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/workqueue.h>
-#include <linux/rcupdate.h>
 #include <linux/file.h>
 #include <linux/slab.h>
 
@@ -139,9 +138,8 @@ static void *vhost_test_stop_vq(struct vhost_test *n,
 	void *private;
 
 	mutex_lock(&vq->mutex);
-	private = rcu_dereference_protected(vq->private_data,
-					 lockdep_is_held(&vq->mutex));
-	rcu_assign_pointer(vq->private_data, NULL);
+	private = vq->private_data;
+	vq->private_data = NULL;
 	mutex_unlock(&vq->mutex);
 	return private;
 }
@@ -205,9 +203,8 @@ static long vhost_test_run(struct vhost_test *n, int test)
 		priv = test ? n : NULL;
 
 		/* start polling new socket */
-		oldpriv = rcu_dereference_protected(vq->private_data,
-						    lockdep_is_held(&vq->mutex));
-		rcu_assign_pointer(vq->private_data, priv);
+		oldpriv = vq->private_data;
+		vq->private_data = priv;
 
 		r = vhost_init_used(&n->vqs[index].vq);
 
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 51aeb5f..2a8c655 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -103,14 +103,8 @@ struct vhost_virtqueue {
 	struct iovec iov[UIO_MAXIOV];
 	struct iovec *indirect;
 	struct vring_used_elem *heads;
-	/* We use a kind of RCU to access private pointer.
-	 * All readers access it from worker, which makes it possible to
-	 * flush the vhost_work instead of synchronize_rcu. Therefore readers do
-	 * not need to call rcu_read_lock/rcu_read_unlock: the beginning of
-	 * vhost_work execution acts instead of rcu_read_lock() and the end of
-	 * vhost_work execution acts instead of rcu_read_unlock().
-	 * Writers use virtqueue mutex. */
-	void __rcu *private_data;
+	/* Protected by virtqueue mutex. */
+	void *private_data;
 	/* Log write descriptors */
 	void __user *log_base;
 	struct vhost_log *log;
-- 
1.8.1.4

Re: [PATCH 0/4] vhost private_data rcu removal

[Michael S. Tsirkin]

On Tue, May 07, 2013 at 02:54:32PM +0800, Asias He wrote:
> Asias He (4):
>   vhost-net: Always access vq->private_data under vq mutex
>   vhost-test: Always access vq->private_data under vq mutex
>   vhost-scsi: Always access vq->private_data under vq mutex
>   vhost: Remove custom vhost rcu usage

Looks good, I'll queue this up for 3.11.

>  drivers/vhost/net.c   | 37 ++++++++++++++++---------------------
>  drivers/vhost/scsi.c  | 17 ++++++-----------
>  drivers/vhost/test.c  | 20 +++++++++-----------
>  drivers/vhost/vhost.h | 10 ++--------
>  4 files changed, 33 insertions(+), 51 deletions(-)
> 
> -- 
> 1.8.1.4