Re: [bug, netconsole, SLUB] BUG skbuff_head_cache: Poisonoverwritten

From: Ingo Molnar
Date: Thu Jul 17 2008 - 20:18:20 EST

* Vegard Nossum <vegard.nossum@xxxxxxxxx> wrote:

> On Fri, Jul 18, 2008 at 1:52 AM, Ingo Molnar <mingo@xxxxxxx> wrote:
> > If only we had some kernel technology that could track and validate
> > memory accesses, and point out the cases where we access uninitialized
> > memory, just like Valgrind?
> >
> > ... something like kmemcheck? ;-)
> Cool :)
> > So i booted that box with tip/master and kmemcheck enabled. (plus a few
> > fixlets to make networking allocations be properly tracked by
> > kmemcheck.)
> >
> > It was a slow bootup and long wait, but it gave a few hits here:
> Hm, if you think it was that slow, I am suspecting you were also using
> SLUB debugging.


# CONFIG_SLUB_DEBUG is not set

> This can actually be negative, since now SLUB will access the objects
> (+redzone +padding) and possibly trick kmemcheck into thinking they
> were initialized in the first place.
> But what we are really looking for is "read from freed memory"
> messages. So I would actually recommend this: Disable kmemcheck's
> reporting of uninitialized memory, simply to make it easier to spot
> the "freed" messages more easily.
> Maybe something like this (warning: whitespace-munged):

ok, applied this too.

> If this only happens during boot, it would also be a good idea to
> simply reboot the machine a lot...

yeah, i've got a script for that. Will try it overnight.

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