linux-kernel - Re: [PATCH 086/117] Staging: hv: storvsc: Leverage the spinlock to manage ref

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Message-ID: <20110824025737.GA30779@kroah.com>
Date:	Tue, 23 Aug 2011 19:57:37 -0700
From:	Greg KH <greg@...ah.com>
To:	KY Srinivasan <kys@...rosoft.com>
Cc:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"virtualization@...ts.osdl.org" <virtualization@...ts.osdl.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: Re: [PATCH 086/117] Staging: hv: storvsc: Leverage the spinlock to
 manage ref_cnt

On Wed, Aug 24, 2011 at 12:58:36AM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Greg KH [mailto:greg@...ah.com]
> > Sent: Tuesday, August 23, 2011 7:10 PM
> > To: KY Srinivasan
> > Cc: gregkh@...e.de; linux-kernel@...r.kernel.org;
> > devel@...uxdriverproject.org; virtualization@...ts.osdl.org; Haiyang Zhang
> > Subject: Re: [PATCH 086/117] Staging: hv: storvsc: Leverage the spinlock to
> > manage ref_cnt
> > 
> > On Fri, Jul 15, 2011 at 10:47:14AM -0700, K. Y. Srinivasan wrote:
> > > Now that we have a spin lock protecting access to the stor device pointer,
> > > use it manage the reference count as well.
> > >
> > > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> > > Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
> > > ---
> > >  drivers/staging/hv/hyperv_storage.h |    8 ++++----
> > >  drivers/staging/hv/storvsc.c        |   10 +++++-----
> > >  2 files changed, 9 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/staging/hv/hyperv_storage.h
> > b/drivers/staging/hv/hyperv_storage.h
> > > index 53b65be..d946211 100644
> > > --- a/drivers/staging/hv/hyperv_storage.h
> > > +++ b/drivers/staging/hv/hyperv_storage.h
> > > @@ -265,7 +265,7 @@ struct storvsc_device {
> > >  	struct hv_device *device;
> > >
> > >  	/* 0 indicates the device is being destroyed */
> > > -	atomic_t ref_count;
> > > +	int	 ref_count;
> > 
> > Is this really needed?  Can't you rely on the reference count of the
> > hv_device itself?
> 
> We don't have a reference count on the hv_device

Wait, why not?  You shure better have a reference count on that device
if you have a pointer to it, if not, you have a bug, and that needs to
be fixed.  Please reread Documentation/CodingStyle for details.

> and this count is taken to deal with racing unloads and incoming
> traffic on the channel from the host. 

Is this something that all other storage drivers have to do?  If not,
then you shouldn't be doing that as well.

greg k-h
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