[v4,3/5] vsock/virtio: fix locking in virtio_transport_inc_tx_pkt()
diff mbox series

Message ID 20190717113030.163499-4-sgarzare@redhat.com
State In Next
Commit 9632e9f61bc4191411c47933abe5f2d93c578f5e
Headers show
Series
  • vsock/virtio: optimizations to increase the throughput
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Commit Message

Stefano Garzarella July 17, 2019, 11:30 a.m. UTC
fwd_cnt and last_fwd_cnt are protected by rx_lock, so we should use
the same spinlock also if we are in the TX path.

Move also buf_alloc under the same lock.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
---
 include/linux/virtio_vsock.h            | 2 +-
 net/vmw_vsock/virtio_transport_common.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

Comments

Michael S. Tsirkin July 17, 2019, 2:51 p.m. UTC | #1
On Wed, Jul 17, 2019 at 01:30:28PM +0200, Stefano Garzarella wrote:
> fwd_cnt and last_fwd_cnt are protected by rx_lock, so we should use
> the same spinlock also if we are in the TX path.
> 
> Move also buf_alloc under the same lock.
> 
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

Wait a second is this a bugfix?
If it's used under the wrong lock won't values get corrupted?
Won't traffic then stall or more data get to sent than
credits?

> ---
>  include/linux/virtio_vsock.h            | 2 +-
>  net/vmw_vsock/virtio_transport_common.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> index 49fc9d20bc43..4c7781f4b29b 100644
> --- a/include/linux/virtio_vsock.h
> +++ b/include/linux/virtio_vsock.h
> @@ -35,7 +35,6 @@ struct virtio_vsock_sock {
>  
>  	/* Protected by tx_lock */
>  	u32 tx_cnt;
> -	u32 buf_alloc;
>  	u32 peer_fwd_cnt;
>  	u32 peer_buf_alloc;
>  
> @@ -43,6 +42,7 @@ struct virtio_vsock_sock {
>  	u32 fwd_cnt;
>  	u32 last_fwd_cnt;
>  	u32 rx_bytes;
> +	u32 buf_alloc;
>  	struct list_head rx_queue;
>  };
>  
> diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> index a85559d4d974..34a2b42313b7 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -210,11 +210,11 @@ static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
>  
>  void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
>  {
> -	spin_lock_bh(&vvs->tx_lock);
> +	spin_lock_bh(&vvs->rx_lock);
>  	vvs->last_fwd_cnt = vvs->fwd_cnt;
>  	pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
>  	pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc);
> -	spin_unlock_bh(&vvs->tx_lock);
> +	spin_unlock_bh(&vvs->rx_lock);
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_inc_tx_pkt);
>  
> -- 
> 2.20.1
Stefano Garzarella July 18, 2019, 7:43 a.m. UTC | #2
On Wed, Jul 17, 2019 at 4:51 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Wed, Jul 17, 2019 at 01:30:28PM +0200, Stefano Garzarella wrote:
> > fwd_cnt and last_fwd_cnt are protected by rx_lock, so we should use
> > the same spinlock also if we are in the TX path.
> >
> > Move also buf_alloc under the same lock.
> >
> > Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
>
> Wait a second is this a bugfix?
> If it's used under the wrong lock won't values get corrupted?
> Won't traffic then stall or more data get to sent than
> credits?

Before this series, we only read vvs->fwd_cnt and vvs->buf_alloc in this
function, but using a different lock than the one used to write them.
I'm not sure if a corruption can happen, but if we want to avoid the
lock, we should use an atomic operation or memory barriers.

Since now we also need to update vvs->last_fwd_cnt, in order to limit the
credit message, I decided to take the same lock used to protect vvs->fwd_cnt
and vvs->last_fwd_cnt.


Thanks,
Stefano

>
> > ---
> >  include/linux/virtio_vsock.h            | 2 +-
> >  net/vmw_vsock/virtio_transport_common.c | 4 ++--
> >  2 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> > index 49fc9d20bc43..4c7781f4b29b 100644
> > --- a/include/linux/virtio_vsock.h
> > +++ b/include/linux/virtio_vsock.h
> > @@ -35,7 +35,6 @@ struct virtio_vsock_sock {
> >
> >       /* Protected by tx_lock */
> >       u32 tx_cnt;
> > -     u32 buf_alloc;
> >       u32 peer_fwd_cnt;
> >       u32 peer_buf_alloc;
> >
> > @@ -43,6 +42,7 @@ struct virtio_vsock_sock {
> >       u32 fwd_cnt;
> >       u32 last_fwd_cnt;
> >       u32 rx_bytes;
> > +     u32 buf_alloc;
> >       struct list_head rx_queue;
> >  };
> >
> > diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
> > index a85559d4d974..34a2b42313b7 100644
> > --- a/net/vmw_vsock/virtio_transport_common.c
> > +++ b/net/vmw_vsock/virtio_transport_common.c
> > @@ -210,11 +210,11 @@ static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
> >
> >  void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
> >  {
> > -     spin_lock_bh(&vvs->tx_lock);
> > +     spin_lock_bh(&vvs->rx_lock);
> >       vvs->last_fwd_cnt = vvs->fwd_cnt;
> >       pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
> >       pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc);
> > -     spin_unlock_bh(&vvs->tx_lock);
> > +     spin_unlock_bh(&vvs->rx_lock);
> >  }
> >  EXPORT_SYMBOL_GPL(virtio_transport_inc_tx_pkt);
> >
> > --
> > 2.20.1
Stefan Hajnoczi July 22, 2019, 8:53 a.m. UTC | #3
On Wed, Jul 17, 2019 at 01:30:28PM +0200, Stefano Garzarella wrote:
> fwd_cnt and last_fwd_cnt are protected by rx_lock, so we should use
> the same spinlock also if we are in the TX path.
> 
> Move also buf_alloc under the same lock.
> 
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
>  include/linux/virtio_vsock.h            | 2 +-
>  net/vmw_vsock/virtio_transport_common.c | 4 ++--
>  2 files changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

Patch
diff mbox series

diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index 49fc9d20bc43..4c7781f4b29b 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -35,7 +35,6 @@  struct virtio_vsock_sock {
 
 	/* Protected by tx_lock */
 	u32 tx_cnt;
-	u32 buf_alloc;
 	u32 peer_fwd_cnt;
 	u32 peer_buf_alloc;
 
@@ -43,6 +42,7 @@  struct virtio_vsock_sock {
 	u32 fwd_cnt;
 	u32 last_fwd_cnt;
 	u32 rx_bytes;
+	u32 buf_alloc;
 	struct list_head rx_queue;
 };
 
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index a85559d4d974..34a2b42313b7 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -210,11 +210,11 @@  static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
 
 void virtio_transport_inc_tx_pkt(struct virtio_vsock_sock *vvs, struct virtio_vsock_pkt *pkt)
 {
-	spin_lock_bh(&vvs->tx_lock);
+	spin_lock_bh(&vvs->rx_lock);
 	vvs->last_fwd_cnt = vvs->fwd_cnt;
 	pkt->hdr.fwd_cnt = cpu_to_le32(vvs->fwd_cnt);
 	pkt->hdr.buf_alloc = cpu_to_le32(vvs->buf_alloc);
-	spin_unlock_bh(&vvs->tx_lock);
+	spin_unlock_bh(&vvs->rx_lock);
 }
 EXPORT_SYMBOL_GPL(virtio_transport_inc_tx_pkt);