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Message-ID: <Pine.LNX.4.64.0706011340110.4323@schroedinger.engr.sgi.com>
Date: Fri, 1 Jun 2007 13:43:04 -0700 (PDT)
From: Christoph Lameter <clameter@....com>
To: Paul Jackson <pj@....com>
cc: srinivasa@...ibm.com, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
vatsa@...ibm.com, dino@...ibm.com, simon.derr@...l.net,
clameter@...ulhu.engr.sgi.com, rientjes@...gle.com
Subject: Re: [RFC] [PATCH] cpuset operations causes Badness at mm/slab.c:777
warning
On Fri, 1 Jun 2007, Paul Jackson wrote:
> > There are no checks necessary. Your function worked fine so far for
> > the case of zero objects with the pointer returned by kmalloc. If the
> > code is correct then it will not dereference the pointer to the zero
> > sized array. If not then we may find a bug and fix it.
>
> I suspect you got lucky. The check for a full pidarray[] in the routine
> pid_array_load() occurs -after- a pid is put in the array. If a task
> showed up in this cpuset at the wrong time, we would fall over and die
> in the code:
Then you are deferencing an element in the pidarray that you did not
allocate! This is a bug in cpuset code. So we would need to allocate at
mininum one array element? Or would we need to allocate npids + 1 to be
safe???
---
kernel/cpuset.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Index: linux-2.6/kernel/cpuset.c
===================================================================
--- linux-2.6.orig/kernel/cpuset.c 2007-06-01 13:41:24.000000000 -0700
+++ linux-2.6/kernel/cpuset.c 2007-06-01 13:42:08.000000000 -0700
@@ -1741,7 +1741,7 @@ static int cpuset_tasks_open(struct inod
* show up until sometime later on.
*/
npids = atomic_read(&cs->count);
- pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
+ pidarray = kmalloc(max(1, npids) * sizeof(pid_t), GFP_KERNEL);
if (!pidarray)
goto err1;
-
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