Date: Thu, 13 Apr 2017 10:24:38 -0700
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>, linux-kernel@vger.kernel.org,
        mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
        akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
        josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
        dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com,
        oleg@redhat.com, bobby.prani@gmail.com,
        Christoph Lameter <cl@linux.com>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, linux-mm@kvack.org
Subject: Re: [PATCH tip/core/rcu 01/13] mm: Rename SLAB_DESTROY_BY_RCU to
 SLAB_TYPESAFE_BY_RCU
Reply-To: paulmck@linux.vnet.ibm.com
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On Thu, Apr 13, 2017 at 06:17:09PM +0200, Peter Zijlstra wrote:
> 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.
> 
> git log -S SLAB_DESTROY_BY_RCU

My (perhaps naive) hope is that having more than one path to
the information will reduce the number of "Whatever happened to
SLAB_DESTROY_BY_RCU?" queries.

							Thanx, Paul