linux-kernel - Re: [RFC] rcu: doc: update example about stale data

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Date:   Tue, 30 Oct 2018 17:58:33 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [RFC] rcu: doc: update example about stale data

On Tue, Oct 30, 2018 at 04:50:39PM -0700, Paul E. McKenney wrote:
> On Sun, Oct 28, 2018 at 06:16:31PM -0700, Joel Fernandes wrote:
> > On Sun, Oct 28, 2018 at 10:21:42AM -0700, Paul E. McKenney wrote:
> > > On Sat, Oct 27, 2018 at 07:16:53PM -0700, Joel Fernandes (Google) wrote:
> > > > The RCU example for 'rejecting stale data' on system-call auditting
> > > > stops iterating through the rules if a deleted one is found. It makes
> > > > more sense to continue looking at other rules once a deleted one is
> > > > rejected. Although the original example is fine, this makes it more
> > > > meaningful.
> > > > 
> > > > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > > 
> > > Does the actual audit code that this was copied from now include the
> > > continue statement?  If so, please update the commit log to state that
> > > and then I will take the resulting patch.  (This example was inspired
> > > by a long-ago version of the actual audit code.)
> > 
> > The document talks of a situation that could be but is not really in the
> > implementation. It says "If the system-call audit module were to ever need to
> > reject stale data". So its not really something implemented. I was just
> > correcting the example you had there since it made more sense to me to
> > continue looking for other rules in the list once a rule was shown to be
> > stale. It just makes the example more correct.
> > 
> > But I'm Ok if you want to leave that alone ;-) Hence, the RFC tag to this
> > patch ;-)
> 
> Well, I do agree that there are situations where you need to keep
> going.  But in the common case where only one instance of a given key
> is allowed, and where the list is either (1) sorted and/or (2) added
> to at the beginning, if you find a deleted element with a given key,
> you are guaranteed that you won't find another with that key even if
> you continue scanning the list.  After all, if you did find a deleted
> element, the duplicate either is not on the list in the sorted case
> or is behind you in the add-at-front case.
> 
> And in the more complex cases where persistent searching is required,
> you usually have to restart the search instead of continuing it.  Besides,
> things like the Issaquah Challenge don't seem to belong in introductory
> documentation on RCU.  ;-)

Ok, agreed. Lets drop this :)

-Joel