vhost: move memory pointer to VQs

commit 2ae76693b8bcabf370b981cd00c36cd41d33fabc
    vhost: replace rcu with mutex
replaced rcu sync for memory accesses with VQ mutex locl/unlock.
This is correct since all accesses are under VQ mutex, but incomplete:
we still do useless rcu lock/unlock operations, someone might copy this
code into some other context where this won't be right.
This use of RCU is also non standard and hard to understand.
Let's copy the pointer to each VQ structure, this way
the access rules become straight-forward, and there's
no need for RCU anymore.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index ff454a0ec6f5..3eda654b8f5a 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -104,6 +104,7 @@ struct vhost_virtqueue {
         struct iovec *indirect;
         struct vring_used_elem *heads;
         /* Protected by virtqueue mutex. */
+        struct vhost_memory *memory;
         void *private_data;
         unsigned acked_features;
         /* Log write descriptors */
@@ -112,10 +113,7 @@ struct vhost_virtqueue {
 };
 
 struct vhost_dev {
-        /* Readers use RCU to access memory table pointer
-         * log base pointer and features.
-         * Writers use mutex below.*/
-        struct vhost_memory __rcu *memory;
+        struct vhost_memory *memory;
         struct mm_struct *mm;
         struct mutex mutex;
         struct vhost_virtqueue **vqs;
@@ -140,7 +138,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp);
 int vhost_vq_access_ok(struct vhost_virtqueue *vq);
 int vhost_log_access_ok(struct vhost_dev *);
 
-int vhost_get_vq_desc(struct vhost_dev *, struct vhost_virtqueue *,
+int vhost_get_vq_desc(struct vhost_virtqueue *,
                       struct iovec iov[], unsigned int iov_count,
                       unsigned int *out_num, unsigned int *in_num,
                       struct vhost_log *log, unsigned int *log_num);