From mboxrd@z Thu Jan 1 00:00:00 1970 From: Helge Deller Subject: Re: [PATCH] [workqueue] check values of pwq and wq in print_worker_info() before use Date: Wed, 02 Oct 2013 00:34:53 +0200 Message-ID: <524B4E0D.9050107@gmx.de> References: <20131001203520.GA8248@p100.box> <20131001204352.GA27149@mtj.dyndns.org> <524B364B.3010405@gmx.de> <20131001210348.GB27149@mtj.dyndns.org> <20131001210735.GA27867@mtj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: Libin , linux-kernel@vger.kernel.org, linux-parisc@vger.kernel.org, James Bottomley To: Tejun Heo Return-path: In-Reply-To: <20131001210735.GA27867@mtj.dyndns.org> List-ID: List-Id: linux-parisc.vger.kernel.org On 10/01/2013 11:07 PM, Tejun Heo wrote: > On Tue, Oct 01, 2013 at 05:03:48PM -0400, Tejun Heo wrote: >> On Tue, Oct 01, 2013 at 10:53:31PM +0200, Helge Deller wrote: >>> So, in summary my patch here is not really necessary, but for the sake of >>> clean code I think it doesn't hurt either and as such it would be nice if >>> you could apply it. >> >> What? function *must* take any value and try to access it and not >> cause failure. That's the *whole* purpose of that interface. How is >> having incomplete spurious checks around it "clean code" in any sense >> of the word? That doesn't make any sense. > > Just in case you didn't know already. probe_kernel_read()'s role is > to take any ulong value and dereference it if it can. If not, it can > return any value, but it shouldn't crash in any case. If you're just > adding NULL test in probe_kernel_read(), you're just masking a common > failure pattern and the kernel still *will* panic while dumping the > states. If a specific arch doesn't have proper probe_kernel_read() > implementation, adding if (!NULL) test there could be a temporary > workaround, but it should be clearly marked as such. Sure, probe_kernel_read() takes care that no segfaults will happen. Nevertheless, if we know that "pwq" might become NULL, why access pwq->wq at all? struct pool_workqueue *pwq = NULL; probe_kernel_read(&wq, &pwq>wq, sizeof(wq)); If you wouldn't have used probe_kernel_read() you would never code it like that. That's what I meant when I wrote "clean coding" (aka "similar to what you would have done without probe_kernel_read()"). Helge