Re: kmemcheck caught read from freed memory (cfq_free_io_context)

On Wed, Apr 02 2008, Pekka Enberg wrote:
Hi Paul,

On Wed, Apr 2, 2008 at 1:55 PM, Paul E. McKenney
<paulmck@xxxxxxxxxxxxxxxxxx> wrote:
I will check this when I get back to some bandwidth -- but in the meantime,
does kmemcheck special-case SLAB_DESTROY_BY_RCU? It is legal to access
newly-freed items in that case, as long as you did rcu_read_lock()
before gaining a reference to them and don't hold the reference past
the matching rcu_read_unlock().

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.

Makes sense, and to me Pauls analysis of the code looks totally correct
- there's no bug there, at least related to hlist traversal and
kmem_cache_free(), since we are under rcu_read_lock() and thus hold off
the grace for freeing.

--
Jens Axboe

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages