linux-kernel - Re: [PATCH] [1/11] Add rcustring ADT for RCU protected strings

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Message-ID: <20091222205912.GD9279@linux.vnet.ibm.com>
Date:	Tue, 22 Dec 2009 12:59:12 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org, ebiederm@...ssion.com
Subject: Re: [PATCH] [1/11] Add rcustring ADT for RCU protected strings

On Tue, Dec 22, 2009 at 11:05:53AM +0100, Andi Kleen wrote:
> On Mon, Dec 21, 2009 at 06:46:35PM -0800, Paul E. McKenney wrote:
> > My guess is that you will sooner or later need a size field, perhaps
> > under some debug config parameter.
> 
> That can be gotten from ksize() if needed.

Fair enough!!!

> > > +/*
> > > + * Get a local private copy of a RCU protected string.
> > > + * Mostly useful to get a string that is stable while sleeping.
> > > + * Caller must free returned string.
> > > + */
> > > +char *access_rcu_string(const char *str, int size, gfp_t gfp)
> > > +{
> > > +	char *copy = kmalloc(size, gfp);
> > > +	if (!str)
> > > +		return NULL;
> > 
> > Assuming that "str" points to the "str" field of a struct rcu_string,
> > what prevents a grace period from elapsing at this point, freeing the
> > "str" out from under us?
> 
> Yes, that's broken thanks. I'll move the reference into the read lock
> section.

Looking forward to seeing the updated version!

							Thanx, Paul
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