From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: Possible deadlock related to CPU hotplug and kernfs Date: Tue, 8 Sep 2015 12:40:08 +0200 Message-ID: <20150908104008.GD3644@twins.programming.kicks-ass.net> References: <55E54FE2.7030601@linux.intel.com> <55ED0057.1000806@linux.intel.com> <2165815.z3RZSlC1oy@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <2165815.z3RZSlC1oy@vostro.rjw.lan> Sender: linux-kernel-owner@vger.kernel.org To: "Rafael J. Wysocki" Cc: Jiang Liu , mingo@kernel.org, "Rafael J. Wysocki" , Tejun Heo , linux hotplug mailing , Linux Kernel Mailing List , ACPI Devel Maling List List-Id: linux-acpi@vger.kernel.org On Mon, Sep 07, 2015 at 11:33:21PM +0200, Rafael J. Wysocki wrote: > On Monday, September 07, 2015 11:11:19 AM Jiang Liu wrote: > Peter, Ingo, some help from lockdep expert is needed. > > We have a splat that almost certainly is a false positive (the original report > is here http://marc.info/?l=linux-kernel&m=144109156901959&w=4) and no ideas > how to make it go away. Can you please have a look and advise? I can't even find the relevant code :/ >>From that email I get kernfs_fop_write() which calls kernfs_get_active(), but that does _NOT_ call cpu_up(), so that callchain is shite. The actual lockdep splat is also not really helpful, and is spraying names over: acpi, device, sysfs and kernfs (do we really need that many layeres of obfuscation for a simple file?) So, please, start by explaining the thing proper such that simple people like me know what to look for.