linux-kernel - RE: [PATCH 3/3] hv: vmbus_open(): reset the channel state on ENOMEM

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Date:	Fri, 30 Jan 2015 05:03:23 +0000
From:	Dexuan Cui <decui@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"driverdev-devel@...uxdriverproject.org" 
	<driverdev-devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	KY Srinivasan <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH 3/3] hv: vmbus_open(): reset the channel state on ENOMEM

> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Thursday, January 29, 2015 21:22 PM
> To: Dexuan Cui
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; driverdev-
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> jasowang@...hat.com; KY Srinivasan; Haiyang Zhang
> Subject: Re: [PATCH 3/3] hv: vmbus_open(): reset the channel state on ENOMEM
> 
> Dexuan Cui <decui@...rosoft.com> writes:
> 
> > Without this patch, the state is put to CHANNEL_OPENING_STATE, and when
> > the driver is loaded next time, vmbus_open() will fail immediately due to
> > newchannel->state != CHANNEL_OPEN_STATE.
> 
> The patch makes sense, but I have one small doubt. We call vmbus_open
> from probe functions of various devices. E.g. in hyperv-keyboard we
> have:
>  error = vmbus_open(...)
>  if (error)
>      goto err_free_mem;
> 
> and we don't call vmbus_close(...) on this path so no
> CHANNELMSG_CLOSECHANNEL will be send.
Exactly.

> Who's gonna retry probe?
The user can try 'rmmod' and 'modprobe' the module to re-probe.

> Wouldn't it be better to close the channel?
Good question!

In your example, due to " goto err_free_mem", we don't run
vmbus_close(), so the memory allocated for the ringbuffer is actually leaked!

Next time when we reload the module, vmbus_open() will allocate new
memory for the ringbuffer.

KY, Haiyang,
Can you please confirm this issue?

Thanks,
-- Dexuan

> 
> >
> > CC: "K. Y. Srinivasan" <kys@...rosoft.com>
> > Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> > ---
> >  drivers/hv/channel.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> > index 2978f5e..26dcf26 100644
> > --- a/drivers/hv/channel.c
> > +++ b/drivers/hv/channel.c
> > @@ -89,9 +89,10 @@ int vmbus_open(struct vmbus_channel *newchannel,
> u32 send_ringbuffer_size,
> >  	out = (void *)__get_free_pages(GFP_KERNEL|__GFP_ZERO,
> >  		get_order(send_ringbuffer_size + recv_ringbuffer_size));
> >
> > -	if (!out)
> > -		return -ENOMEM;
> > -
> > +	if (!out) {
> > +		err = -ENOMEM;
> > +		goto error0;
> > +	}
> >
> >  	in = (void *)((unsigned long)out + send_ringbuffer_size);
> >
> > @@ -199,6 +200,7 @@ error0:
> >  	free_pages((unsigned long)out,
> >  		get_order(send_ringbuffer_size + recv_ringbuffer_size));
> >  	kfree(open_info);
> > +	newchannel->state = CHANNEL_OPEN_STATE;
> >  	return err;
> >  }
> >  EXPORT_SYMBOL_GPL(vmbus_open);
> 
> --
>   Vitaly
--
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