Subject: Re: [PATCH 02/36] scsi,rcu: convert call_rcu(fc_rport_free_rcu) to kfree_rcu()

From: "Paul E. McKenney" <[email-masked]>
Date: Tue, 22 Mar 2011 23:50:14 -0700

On Tue, Mar 22, 2011 at 10:28:33AM -0700, Robert Love wrote:
> On Thu, 2011-03-17 at 20:41 -0700, Lai Jiangshan wrote:
> > 
> > The rcu callback fc_rport_free_rcu() just calls a kfree(),
> > so we use kfree_rcu() instead of the call_rcu(fc_rport_free_rcu).
> > 
> > Signed-off-by: Lai Jiangshan <[email-masked]>
> > ---
> >  drivers/scsi/libfc/fc_rport.c |   14 +-------------
> >  1 files changed, 1 insertions(+), 13 deletions(-)
> > 
> > diff --git a/drivers/scsi/libfc/fc_rport.c b/drivers/scsi/libfc/fc_rport.c
> > index a7175ad..29abab0 100644
> > --- a/drivers/scsi/libfc/fc_rport.c
> > +++ b/drivers/scsi/libfc/fc_rport.c
> > @@ -151,18 +151,6 @@ static struct fc_rport_priv *fc_rport_create(struct fc_lport *lport,
> >  }
> >  
> >  /**
> > - * fc_rport_free_rcu() - Free a remote port
> > - * @rcu: The rcu_head structure inside the remote port
> > - */
> > -static void fc_rport_free_rcu(struct rcu_head *rcu)
> > -{
> > -	struct fc_rport_priv *rdata;
> > -
> > -	rdata = container_of(rcu, struct fc_rport_priv, rcu);
> > -	kfree(rdata);
> > -}
> > -
> > -/**
> >   * fc_rport_destroy() - Free a remote port after last reference is released
> >   * @kref: The remote port's kref
> >   */
> > @@ -171,7 +159,7 @@ static void fc_rport_destroy(struct kref *kref)
> >  	struct fc_rport_priv *rdata;
> >  
> >  	rdata = container_of(kref, struct fc_rport_priv, kref);
> > -	call_rcu(&rdata->rcu, fc_rport_free_rcu);
> > +	kfree_rcu(rdata, rcu);
> 
> I think this last line should be:
> 
> kfree_rcu(rdata, &rdata->rcu);

Hello, Robert,

I believe that it is correct as is.  The kfree_rcu() definition is as
follows:

#define kfree_rcu(ptr, rcu_head)					\
	__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))

Then __kfree_rcu() encodes the offset into the rcu_head so that it can
be handled properly at the end of the grace period.

							Thanx, Paul