linux-kernel - Re: [Pv-drivers] [PATCH 05/12] VMCI: event handling implementation.

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Message-ID: <20121030045821.GD32055@dtor-ws.eng.vmware.com>
Date:	Mon, 29 Oct 2012 21:58:21 -0700
From:	Dmitry Torokhov <dtor@...are.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	George Zhang <georgezhang@...are.com>, pv-drivers@...are.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [Pv-drivers] [PATCH 05/12] VMCI: event handling implementation.

On Mon, Oct 29, 2012 at 07:24:46PM -0700, Greg KH wrote:
> On Mon, Oct 29, 2012 at 06:04:27PM -0700, George Zhang wrote:
> > +/*
> > + * Releases the given VMCISubscription.
> > + * Fires the destroy event if the reference count has gone to zero.
> > + */
> > +static void event_release(struct vmci_subscription *entry)
> > +{
> > +	kref_put(&entry->kref, event_signal_destroy);
> > +}
> 
> Same question as before with the kref_put() call, what is handling the
> locking here?  It looks like a race to me.

The reference is taken only if event is on the list (which managed by
RCU and a mutex), so it is not possible to go from 0->1 for that
refcount.

Thanks,
Dmitry

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