linux-kernel - Re: [PATCH] State limits to safety of

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Message-ID: <20070913152107.GC12806@linux.vnet.ibm.com>
Date:	Thu, 13 Sep 2007 08:21:07 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Matthew Helsley <matthltc@...ibm.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] State limits to safety of _safe iterators

On Thu, Sep 13, 2007 at 02:22:45AM -0700, Matthew Helsley wrote:
> On Wed, 2007-09-12 at 18:01 -0700, Paul E. McKenney wrote:
> > The _safe list iterators make a blanket statement about how they are
> > safe against removal.  This patch, inspired by private conversations
> > with people who unwisely but perhaps understandably took this blanket
> > statement at its word, adds comments stating limits to this safety.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> > 
> >  list.h |   42 ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 42 insertions(+)
> > 
> > diff -urpNa -X dontdiff linux-2.6.22/include/linux/list.h linux-2.6.22-safedoc/include/linux/list.h
> > --- linux-2.6.22/include/linux/list.h	2007-07-08 16:32:17.000000000 -0700
> > +++ linux-2.6.22-safedoc/include/linux/list.h	2007-09-12 17:45:38.000000000 -0700
> > @@ -472,6 +472,12 @@ static inline void list_splice_init_rcu(
> >   * @pos:	the &struct list_head to use as a loop cursor.
> >   * @n:		another &struct list_head to use as temporary storage
> >   * @head:	the head for your list.
> > + *
> > + * Please note that this is safe only against removal by the code in
> 
> I'm not trying to be snarky but how far should we go before expecting
> folks to read the macros? Depending on the answer you may also want to
> mention that without additional additional code it's safe only against
> removal of the list element at pos.

Good question.  In fact, I would have agreed with you before coming
across people who in my experience are generally reasonably well clued
in who were confused about this.

							Thanx, Paul
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