netdev - Re: WARNING: at mm/slub.c:3357, kernel BUG at mm/slub.c:3413

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Date:	Tue, 22 Nov 2011 17:32:59 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Christian Kujau <lists@...dbynature.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"Alex,Shi" <alex.shi@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: WARNING: at mm/slub.c:3357, kernel BUG at mm/slub.c:3413

Le mardi 22 novembre 2011 à 10:20 -0600, Christoph Lameter a écrit :
> Argh. The Redzoning (and the general object pad initialization) is outside
> of the slab_lock now. So I get wrong positives on those now. That
> is already in 3.1 as far as I know. To solve that we would have to cover a
> much wider area in the alloc and free with the slab lock.
> 
> But I do not get the count mismatches that you saw. Maybe related to
> preemption. Will try that next.

Also I note the checks (redzoning and all features) that should be done
in kfree() are only done on slow path ???
f
...
stat(s, FREE_SLOWPATH);

if (kmem_cache_debug(s) && !free_debug_processing(s, page, x, addr))
...

This is unfortunate...


I am considering adding a "quarantine" capability : each cpu will
maintain in its struct kmem_cache_cpu a FIFO list of "s->quarantine_max"
freed objects.

So it should be easier to track use after free bugs, setting
quarantine_max to a big value.



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