Re: [bug, netconsole, SLUB] BUG skbuff_head_cache: Poison overwritten
From: Vegard Nossum
Date: Thu Jul 17 2008 - 20:05:54 EST
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? ;-)
> So i booted that box with tip/master and kmemcheck enabled. (plus a few
> fixlets to make networking allocations be properly tracked by
> 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
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):
diff --git a/arch/x86/mm/kmemcheck/error.c b/arch/x86/mm/kmemcheck/error.c
index 56410c6..6944cb7 100644
@@ -98,6 +98,9 @@ void kmemcheck_error_save(enum kmemcheck_shadow state,
prev_ip = regs->ip;
+ if (state == KMEMCHECK_SHADOW_UNINITIALIZED)
e = error_next_wr();
If this only happens during boot, it would also be a good idea to
simply reboot the machine a lot...
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
-- E. W. Dijkstra, EWD1036
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/