linux-kernel - Re: [PATCH] print_worker_info: Handle pointer with more care

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Message-ID: <20130816164544.GK2505@htj.dyndns.org>
Date:	Fri, 16 Aug 2013 12:45:44 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Richard Weinberger <richard@....at>
Cc:	linux-kernel@...r.kernel.org, Jeff Dike <jdike@...toit.com>,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [PATCH] print_worker_info: Handle pointer with more care

Hello,

On Fri, Aug 16, 2013 at 06:38:58PM +0200, Richard Weinberger wrote:
> > cc'ing uml people.  Hey, guys, workqueue uses proble_kernel_read() to
> > print out workqueue related information during oops because those
> > events are completely asynchronous and workqueue states may not be
> > consistently accessible.  It seems like uml doesn't implement
> > probe_kernel_read() and tries direct derference of incorrect pointers
> > leading to its own oops.  Maybe uml should check whether the memory is
> > mapped from probe_kernel_read()?
> 
> You are already talking to UML people. ;)

Ooh... :)

> Anyway, I'll investigate into that.
> What I see so far is that pwq is NULL after probe_kernel_read().

Yeah, and that should be fine.  &pwq->wq would be just an offset of wq
from NULL which is an invalid pointer but probe_kernel_read() should
be able to handle that and probably just return 0 or -1 (all bits
set).  I *think* what's necessary is making probe_kernel_read() use
mincore() to fine out whether the requested address is mapped (it
should return -EFAULT if not) and try to dereference the address iff
it's mapped.

Thanks.

-- 
tejun
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