netdev - Re: Issue with netlink implementation

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Date:	Fri, 03 Apr 2009 22:06:16 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	keyoor.khristi@...il.com
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: Issue with netlink implementation

From: Keyoor Khristi <keyoor.khristi@...il.com>
Date: Sat, 4 Apr 2009 02:54:48 +0530

You might want to ask networking questions on the networking
developer list, netdev@...r.kernel.org, CC:'d

Thank you.

> Hi All,
> 
> We are facing an issue with netlink implementation. We are sending the
> data from user space to kernel space. a kernel thread gets the data
> from netlink socket (via skb_recv_datagram). After doing little bit
> processing we give the skb to driver. driver sends the data and frees
> the skb. Sometimes we observe that the writer thread in userspace gets
> stuck writing a packet and doesnt come out. We traced the problem to
> netlink_attachskb. When a packet is sent on the netlink socket
> netlink_attachskb is called to add the skb to the queue. when there is
> not enough space, the thread is added to nlk->wait queue and issues
> schedule_timeout. it doesnt come out of it as no other thread awakens
> it. It seems when the driver frees the skb, the data is freed and the
> receive space is made available in the destructor but the thread
> waiting is not awaken. This is causing the problem we're seeing.
> I think the netlink implementation in af_netlink.c can be enhanced. In
> netlink_attachskb, after invoking skb_set_owner_r we should change the
> skb->destructor to point to newly added function netlink_rfree. When
> skb is freed, netlink_rfree function can issue sock_rfree and awaken
> the threads waiting on nlk->wait queue.
> 
> Please let me know what you think about it.
> I'm not sure if i've sent the email to correct forum. If i should be
> sending to another forum, please tell me.
> 
> Regards,
> K
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