vhost: Remove custom vhost rcu usage

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>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

4 files changed, 12 insertions, 26 deletions

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 99f8d63491aa..969a85960e9f 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>
 
@@ -749,8 +748,7 @@ 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;
 
@@ -763,10 +761,9 @@ 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;
 }
@@ -922,8 +919,7 @@ 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));
@@ -933,7 +929,7 @@ 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;
@@ -967,7 +963,7 @@ 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_wait_and_free(ubufs);
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 45365396dbbc..35ab0ce98414 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 a73ea217f24d..339eae85859a 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>
 
@@ -200,9 +199,8 @@ 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]);
 
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 42298cd23c73..4465ed5f316d 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;