On Mon, Apr 24, 2006 at 06:23:52PM +0800, Akinobu Mita wrote:
> On Mon, Apr 24, 2006 at 12:20:03PM +0300, Pekka Enberg wrote:
> > > Because use-after-free poisoning make kref counter signed value.
> > > So this patch prevents it by changing poisoning pattern.
> >
> > Then why not check against POISON_INUSE when CONFIG_SLAB_DEBUG in the
> > kref debugging code? I would prefer you didn't change the slab constants
> > (they're well known by everyone now) but if you must, at least stick a
> > big fat comment there.
>
> This slab poisoning pattern change is not very important.
>
> Because even if slab debugging is enalbed, kref_put() with unreferenced
> kref object will be detected as slab corruption.
>
> Because kref_put() decrements the kref counter in freed slab object.
>
> Slab corruption: start=e0e8b698, len=32
> Redzone: 0x5a2cf071/0x5a2cf071.
> Last user: [<f08ea008>](release_test_kref+0x8/0x14 [test])
> 000: 6b 6b 6b 6b 6a 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> ^^
> The main reason I want to propose this kref debugging is because
> I can find many places where we can replace from atomic_t to
> struct kref by doing "grep -r atomic_dec_and_test .".
>
> But I warried that replacing by kref will just increase atomic operations
> because of debugging code in kref (WARN_ON()es in kref.c)
>
> So patch 4/4 is not very important, I want to drop patch 4/4.
It would have conflicted with this, btw:
http://kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.17-rc1/2.6.17-rc1-mm3/broken-out/add-poisonh-and-patch-primary-users.patch
--
Mathematics is the supreme nostalgia of our time.
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