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SubjectRe: Issue with 'lib/vsprintf.c: don't try to fix pointer wrap-around'
On Fri, 16 Jan 2015 11:23:57 -0500 Johannes Weiner <hannes@cmpxchg.org> wrote:

> Hi Rasmus,
>
> I have trouble booting my test machine with this patch in -mm:
>
> commit bb2e066c6943e62e9650bb129f416dacf138f8b1
> Author: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Date: Wed Jan 14 01:00:44 2015 +0000
>
> lib/vsprintf.c: don't try to fix pointer wrap-around
>
> Actual kernel buffers can't wrap into the user address space. If someone
> manages to pass a buf/size combination that wraps, it is most likely due
> to a bug in the caller. Instead of trying to fix it by using a smaller
> part of the buffer, bail out.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Jiri Kosina <jkosina@suse.cz>
> Cc: Randy Dunlap <rdunlap@infradead.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>
> After I get "Loading bzImage-new... ok" from the bootloader, the
> serial console remains quiet.
>
> A WARN_ON_ONCE() inside vsnprintf() looks like it would deadlock
> instantly when triggering this overflow from printk(), no?

Dammit, I was starting at that printk, ended up deciding it was OK,
didn't think about deadlocks. logbuf_lock and recursion_bug, for a
start...

I'll drop the patch. I assume all this means that your machine is
trying to trigger that warning condition? I wonder what the call
site is.



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