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

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Message-ID: <20091222100553.GA10314@basil.fritz.box>
Date:	Tue, 22 Dec 2009 11:05:53 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com
Subject: Re: [PATCH] [1/11] Add rcustring ADT for RCU protected strings

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.

> > +/*
> > + * 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.

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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