Re: [PATCH 086/117] Staging: hv: storvsc: Leverage the spinlock to manage ref_cnt

Greg KH
2011-08-24T03:08:36Z

On Wed, Aug 24, 2011 at 12:58:36AM +0000, KY Srinivasan wrote:
>
>
> > -----Original Message-----
> > From: Greg KH [mailto:greg@kroah.com]
> > Sent: Tuesday, August 23, 2011 7:10 PM
> > To: KY Srinivasan
> > Cc: gregkh@suse.de; linux-kernel@vger.kernel.org;
> > devel@linuxdriverproject.org; virtualization@lists.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@microsoft.com>
> > > Signed-off-by: Haiyang Zhang <haiyangz@microsoft.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