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SubjectRe: kmemcheck caught read from freed memory (cfq_free_io_context)
On Wed, Apr 2, 2008 at 6:08 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> On Wed, Apr 02, 2008 at 02:01:13PM +0300, Pekka Enberg wrote:
> > No, kmemcheck is work in progress and does not know about
> > SLAB_DESTROY_BY_RCU yet. The reason I asked Vegard to post the warning
> > was because Peter, Vegard, and myself identified this particular
> > warning as a real problem. But yeah, kmemcheck can cause false
> > positives for RCU for now.
>
> Would the following be an appropriate fix? It seems to me to be in
> the same spirit as the existing check for s->ctor.

In my opinion, no.

It would fix the false positives, but would in fact also hide cases
such as this one with cfq, e.g. the real cases of mis-use.

Peter Zijlstra suggested this:
> It would have to register an call_rcu callback itself in order to mark
> it freed - and handle the race with the object being handed out again.

I will try to look into this -- for now, I need to understand RCU
first (I've seen your LWN articles -- great work! :-))


Kind regards,
Vegard Nossum


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