linux-kernel - Re: [PATCH tip/core/rcu 01/13] mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY

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Message-Id: <20170413160027.GX3956@linux.vnet.ibm.com>
Date:   Thu, 13 Apr 2017 09:00:27 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, bobby.prani@...il.com,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, linux-mm@...ck.org
Subject: Re: [PATCH tip/core/rcu 01/13] mm: Rename SLAB_DESTROY_BY_RCU to
 SLAB_TYPESAFE_BY_RCU

On Thu, Apr 13, 2017 at 01:06:56PM +0200, Vlastimil Babka wrote:
> On 04/13/2017 11:12 AM, Peter Zijlstra wrote:
> > On Wed, Apr 12, 2017 at 09:55:37AM -0700, Paul E. McKenney wrote:
> >> A group of Linux kernel hackers reported chasing a bug that resulted
> >> from their assumption that SLAB_DESTROY_BY_RCU provided an existence
> >> guarantee, that is, that no block from such a slab would be reallocated
> >> during an RCU read-side critical section.  Of course, that is not the
> >> case.  Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
> >> slab of blocks.
> > 
> > And that while we wrote a huge honking comment right along with it...
> > 
> >> [ paulmck: Add "tombstone" comments as requested by Eric Dumazet. ]
> > 
> > I cannot find any occurrence of "tomb" or "TOMB" in the actual patch,
> > confused?
> 
> It's the comments such as:
> 
> + * Note that SLAB_TYPESAFE_BY_RCU was originally named SLAB_DESTROY_BY_RCU.
> 
> so that people who remember the old name can git grep its fate.

Exactly!

But I must confess that "tombstone" was an excessively obscure word
choice, even for native English speakers.  I have reworded as follows:

[ paulmck: Add comments mentioning the old name, as requested by Eric
  Dumazet, in order to help people familiar with the old name find
  the new one. ]

Does that help?

							Thanx, Paul