From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 16 Aug 2013 12:45:44 -0400 From: Tejun Heo Message-ID: <20130816164544.GK2505@htj.dyndns.org> References: <1376668606-32354-1-git-send-email-richard@nod.at> <20130816161229.GI2505@htj.dyndns.org> <520E500B.5000408@nod.at> <20130816162844.GJ2505@htj.dyndns.org> <520E55A2.9080900@nod.at> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <520E55A2.9080900@nod.at> Sender: linux-kernel-owner@vger.kernel.org Subject: Re: [PATCH] print_worker_info: Handle pointer with more care To: Richard Weinberger Cc: linux-kernel@vger.kernel.org, Jeff Dike , user-mode-linux-devel@lists.sourceforge.net List-ID: 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