Patchwork [V2,3/3] tuntap: don't add to waitqueue when POLLERR

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Submitter Jason Wang
Date Jan. 5, 2013, 9:34 a.m.
Message ID <1357378446-19656-4-git-send-email-jasowang@redhat.com>
Download mbox | patch
Permalink /patch/209656/
State Changes Requested
Delegated to: David Miller
Headers show

Comments

Jason Wang - Jan. 5, 2013, 9:34 a.m.
Currently, tun_chr_poll() returns POLLERR after waitqueue adding during device
unregistration. This would confuse some of its user such as vhost which assume
when POLLERR is returned, it wasn't added to the waitqueue. Fix this by
returning POLLERR before adding to waitqueue.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
 drivers/net/tun.c |    5 +----
 1 files changed, 1 insertions(+), 4 deletions(-)
Eric Dumazet - Jan. 5, 2013, 7:37 p.m.
On Sat, 2013-01-05 at 17:34 +0800, Jason Wang wrote:
> Currently, tun_chr_poll() returns POLLERR after waitqueue adding during device
> unregistration. This would confuse some of its user such as vhost which assume
> when POLLERR is returned, it wasn't added to the waitqueue. Fix this by
> returning POLLERR before adding to waitqueue.
> 
> Signed-off-by: Jason Wang <jasowang@redhat.com>
> ---
>  drivers/net/tun.c |    5 +----
>  1 files changed, 1 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index fbd106e..f9c0049 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -886,7 +886,7 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
>  	struct sock *sk;
>  	unsigned int mask = 0;
>  
> -	if (!tun)
> +	if (!tun || tun->dev->reg_state != NETREG_REGISTERED)
>  		return POLLERR;
>  
>  	sk = tfile->socket.sk;
> @@ -903,9 +903,6 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
>  	     sock_writeable(sk)))
>  		mask |= POLLOUT | POLLWRNORM;
>  
> -	if (tun->dev->reg_state != NETREG_REGISTERED)
> -		mask = POLLERR;
> -
>  	tun_put(tun);
>  	return mask;
>  }

This patch is buggy.

First, the caller assuming POLLERR means poll_wait() was not called is
wrong.

Secondly, you add a ref leak.



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Jason Wang - Jan. 6, 2013, 4:43 a.m.
On 01/06/2013 03:37 AM, Eric Dumazet wrote:
> On Sat, 2013-01-05 at 17:34 +0800, Jason Wang wrote:
>> Currently, tun_chr_poll() returns POLLERR after waitqueue adding during device
>> unregistration. This would confuse some of its user such as vhost which assume
>> when POLLERR is returned, it wasn't added to the waitqueue. Fix this by
>> returning POLLERR before adding to waitqueue.
>>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>>  drivers/net/tun.c |    5 +----
>>  1 files changed, 1 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
>> index fbd106e..f9c0049 100644
>> --- a/drivers/net/tun.c
>> +++ b/drivers/net/tun.c
>> @@ -886,7 +886,7 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
>>  	struct sock *sk;
>>  	unsigned int mask = 0;
>>  
>> -	if (!tun)
>> +	if (!tun || tun->dev->reg_state != NETREG_REGISTERED)
>>  		return POLLERR;
>>  
>>  	sk = tfile->socket.sk;
>> @@ -903,9 +903,6 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
>>  	     sock_writeable(sk)))
>>  		mask |= POLLOUT | POLLWRNORM;
>>  
>> -	if (tun->dev->reg_state != NETREG_REGISTERED)
>> -		mask = POLLERR;
>> -
>>  	tun_put(tun);
>>  	return mask;
>>  }
> This patch is buggy.
>
> First, the caller assuming POLLERR means poll_wait() was not called is
> wrong.

True, looks like vhost need to check the poll->wqh before trying to
remove from waitqueue instead of this wrong assumption. And then we can
drop the whole tx polling state.
>
> Secondly, you add a ref leak.

Yes, will drop this patch.

Thanks.
>
>
>
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Patch

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index fbd106e..f9c0049 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -886,7 +886,7 @@  static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
 	struct sock *sk;
 	unsigned int mask = 0;
 
-	if (!tun)
+	if (!tun || tun->dev->reg_state != NETREG_REGISTERED)
 		return POLLERR;
 
 	sk = tfile->socket.sk;
@@ -903,9 +903,6 @@  static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
 	     sock_writeable(sk)))
 		mask |= POLLOUT | POLLWRNORM;
 
-	if (tun->dev->reg_state != NETREG_REGISTERED)
-		mask = POLLERR;
-
 	tun_put(tun);
 	return mask;
 }