* vhost-net: is there a race for sock in handle_tx/rx?
@ 2012-05-03 8:33 Liu ping fan
2012-05-03 8:41 ` Michael S. Tsirkin
0 siblings, 1 reply; 3+ messages in thread
From: Liu ping fan @ 2012-05-03 8:33 UTC (permalink / raw)
To: netdev; +Cc: Michael S. Tsirkin, kvm, linux-kernel
Hi,
During reading the vhost-net code, I find the following,
static void handle_tx(struct vhost_net *net)
{
struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
unsigned out, in, s;
int head;
struct msghdr msg = {
.msg_name = NULL,
.msg_namelen = 0,
.msg_control = NULL,
.msg_controllen = 0,
.msg_iov = vq->iov,
.msg_flags = MSG_DONTWAIT,
};
size_t len, total_len = 0;
int err, wmem;
size_t hdr_size;
struct socket *sock;
struct vhost_ubuf_ref *uninitialized_var(ubufs);
bool zcopy;
/* TODO: check that we are running from vhost_worker? */
sock = rcu_dereference_check(vq->private_data, 1);
if (!sock)
return;
--------------------------------> Qemu calls
vhost_net_set_backend() to set a new backend fd, and close
@oldsock->file. And sock->file refcnt==0.
Can vhost_worker prevent
itself from such situation? And how?
wmem = atomic_read(&sock->sk->sk_wmem_alloc);
.........................................................................
Is it a race?
Thanks and regards,
pingfan
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: vhost-net: is there a race for sock in handle_tx/rx?
2012-05-03 8:33 vhost-net: is there a race for sock in handle_tx/rx? Liu ping fan
@ 2012-05-03 8:41 ` Michael S. Tsirkin
2012-05-03 9:08 ` Liu ping fan
0 siblings, 1 reply; 3+ messages in thread
From: Michael S. Tsirkin @ 2012-05-03 8:41 UTC (permalink / raw)
To: Liu ping fan; +Cc: netdev, kvm, linux-kernel
On Thu, May 03, 2012 at 04:33:55PM +0800, Liu ping fan wrote:
> Hi,
>
> During reading the vhost-net code, I find the following,
>
> static void handle_tx(struct vhost_net *net)
> {
> struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
> unsigned out, in, s;
> int head;
> struct msghdr msg = {
> .msg_name = NULL,
> .msg_namelen = 0,
> .msg_control = NULL,
> .msg_controllen = 0,
> .msg_iov = vq->iov,
> .msg_flags = MSG_DONTWAIT,
> };
> size_t len, total_len = 0;
> int err, wmem;
> size_t hdr_size;
> struct socket *sock;
> struct vhost_ubuf_ref *uninitialized_var(ubufs);
> bool zcopy;
>
> /* TODO: check that we are running from vhost_worker? */
> sock = rcu_dereference_check(vq->private_data, 1);
> if (!sock)
> return;
>
> --------------------------------> Qemu calls
> vhost_net_set_backend() to set a new backend fd, and close
> @oldsock->file. And sock->file refcnt==0.
>
> Can vhost_worker prevent
> itself from such situation? And how?
>
> wmem = atomic_read(&sock->sk->sk_wmem_alloc);
> .........................................................................
>
> Is it a race?
>
> Thanks and regards,
> pingfan
See comment before void __rcu *private_data in vhost.h
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: vhost-net: is there a race for sock in handle_tx/rx?
2012-05-03 8:41 ` Michael S. Tsirkin
@ 2012-05-03 9:08 ` Liu ping fan
0 siblings, 0 replies; 3+ messages in thread
From: Liu ping fan @ 2012-05-03 9:08 UTC (permalink / raw)
To: Michael S. Tsirkin; +Cc: netdev, kvm, linux-kernel
Oh, got it. It is a very interesting implement.
Thanks and regards,
pingfan
On Thu, May 3, 2012 at 4:41 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Thu, May 03, 2012 at 04:33:55PM +0800, Liu ping fan wrote:
>> Hi,
>>
>> During reading the vhost-net code, I find the following,
>>
>> static void handle_tx(struct vhost_net *net)
>> {
>> struct vhost_virtqueue *vq = &net->dev.vqs[VHOST_NET_VQ_TX];
>> unsigned out, in, s;
>> int head;
>> struct msghdr msg = {
>> .msg_name = NULL,
>> .msg_namelen = 0,
>> .msg_control = NULL,
>> .msg_controllen = 0,
>> .msg_iov = vq->iov,
>> .msg_flags = MSG_DONTWAIT,
>> };
>> size_t len, total_len = 0;
>> int err, wmem;
>> size_t hdr_size;
>> struct socket *sock;
>> struct vhost_ubuf_ref *uninitialized_var(ubufs);
>> bool zcopy;
>>
>> /* TODO: check that we are running from vhost_worker? */
>> sock = rcu_dereference_check(vq->private_data, 1);
>> if (!sock)
>> return;
>>
>> --------------------------------> Qemu calls
>> vhost_net_set_backend() to set a new backend fd, and close
>> @oldsock->file. And sock->file refcnt==0.
>>
>> Can vhost_worker prevent
>> itself from such situation? And how?
>>
>> wmem = atomic_read(&sock->sk->sk_wmem_alloc);
>> .........................................................................
>>
>> Is it a race?
>>
>> Thanks and regards,
>> pingfan
>
> See comment before void __rcu *private_data in vhost.h
>
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-05-03 8:33 vhost-net: is there a race for sock in handle_tx/rx? Liu ping fan
2012-05-03 8:41 ` Michael S. Tsirkin
2012-05-03 9:08 ` Liu ping fan
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