linux-kernel - RE: [PATCH 2/4] Drivers: hv: vmbus: do not lose rescind offer on failure in vmbus_process

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Date:	Wed, 4 Feb 2015 07:42:36 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	KY Srinivasan <kys@...rosoft.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
CC:	Haiyang Zhang <haiyangz@...rosoft.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jason Wang <jasowang@...hat.com>
Subject: RE: [PATCH 2/4] Drivers: hv: vmbus: do not lose rescind offer on
 failure in vmbus_process_offer()

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Wednesday, February 4, 2015 1:01 AM
> To: KY Srinivasan; devel@...uxdriverproject.org
> Cc: Haiyang Zhang; linux-kernel@...r.kernel.org; Dexuan Cui; Jason Wang
> Subject: [PATCH 2/4] Drivers: hv: vmbus: do not lose rescind offer on failure in
> vmbus_process_offer()
> 
> In case we hit a failure condition in vmbus_process_offer() and a rescind offer
> was pending for the channel we just do free_channel() so
> CHANNELMSG_RELID_RELEASED
> will never be send to the host. We have to follow vmbus_process_rescind_offer()
> path anyway.
> 
> To support the change we need to protect list_del in
> vmbus_process_rescind_offer()
> hitting an uninitialized list.
> 
> Reported-by: Dexuan Cui <decui@...rosoft.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  drivers/hv/channel_mgmt.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index eb9ce94..fdccd16 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -152,6 +152,7 @@ static struct vmbus_channel *alloc_channel(void)
>  	spin_lock_init(&channel->inbound_lock);
>  	spin_lock_init(&channel->lock);
> 
> +	INIT_LIST_HEAD(&channel->listentry);
>  	INIT_LIST_HEAD(&channel->sc_list);
>  	INIT_LIST_HEAD(&channel->percpu_list);
> 
> @@ -308,6 +309,7 @@ static void vmbus_process_offer(struct work_struct
> *work)
>  	struct vmbus_channel *channel;
>  	bool fnew = true;
>  	bool enq = false;
> +	bool failure = false;
>  	int ret;
>  	unsigned long flags;
> 
> @@ -408,19 +410,33 @@ static void vmbus_process_offer(struct work_struct
> *work)
>  		spin_lock_irqsave(&vmbus_connection.channel_lock, flags);
>  		list_del(&newchannel->listentry);
>  		spin_unlock_irqrestore(&vmbus_connection.channel_lock,
> flags);
> +		/*
> +		 * Init listentry again as vmbus_process_rescind_offer can try
> +		 * doing list_del again.
> +		 */
> +		INIT_LIST_HEAD(&channel->listentry);
>  		kfree(newchannel->device_obj);
> +		newchannel->device_obj = NULL;
>  		goto err_free_chan;
>  	}
> +	goto done_init_rescind;
> +err_free_chan:
> +	failure = true;
>  done_init_rescind:
> +	/*
> +	 * Get additional reference as vmbus_put_channel() can be called
> +	 * either directly or through vmbus_process_rescind_offer().
> +	 */
> +	vmbus_get_channel(newchannel);
>  	spin_lock_irqsave(&newchannel->lock, flags);
here we get the lock.

>  	/* The next possible work is rescind handling */
>  	INIT_WORK(&newchannel->work, vmbus_process_rescind_offer);
>  	/* Check if rescind offer was already received */
>  	if (newchannel->rescind)
>  		queue_work(newchannel->controlwq, &newchannel->work);
> +	else if (failure)
> +		vmbus_put_channel(newchannel);
Here in vmbus_put_channel(), we try to get the same spinlock -- dead lock.

-- Dexuan

>  	spin_unlock_irqrestore(&newchannel->lock, flags);
> -	return;
> -err_free_chan:
>  	vmbus_put_channel(newchannel);
>  }
> 
> --
> 1.9.3

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