Re: kmemcheck caught read from freed memory (cfq_free_io_context)

["Vegard Nossum" <vegard.nossum@gmail.com>]

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