linux-kernel - Re: Memory allocator semantics

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Date:	Fri, 14 Feb 2014 09:30:39 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: Memory allocator semantics

On Tue, Feb 11, 2014 at 12:43:35PM -0600, Christoph Lameter wrote:
> On Tue, 11 Feb 2014, Pekka Enberg wrote:
> 
> > So again, there's nothing in (A) that the memory allocator is
> > concerned about.  kmalloc() makes no guarantees whatsoever about the
> > visibility of "r1" across CPUs.  If you're saying that there's an
> > implicit barrier between kmalloc() and kfree(), that's an unintended
> > side-effect, not a design decision AFAICT.
> 
> I am not sure that this side effect necessarily happens. The SLUB fastpath
> does not disable interrupts and only uses a cmpxchg without lock
> semantics.

That tells me what I need to know.  Users should definitely not try a
"drive-by kfree()" of something that was concurrently allocated.  ;-)

							Thanx, Paul

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