From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Date: Tue, 08 Sep 2015 22:28:12 +0000 Subject: Re: Possible deadlock related to CPU hotplug and kernfs Message-Id: <4305045.rOCzS8rSge@vostro.rjw.lan> List-Id: References: <55E54FE2.7030601@linux.intel.com> <2165815.z3RZSlC1oy@vostro.rjw.lan> <20150908104008.GD3644@twins.programming.kicks-ass.net> In-Reply-To: <20150908104008.GD3644@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Peter Zijlstra Cc: Jiang Liu , mingo@kernel.org, "Rafael J. Wysocki" , Tejun Heo , linux hotplug mailing , Linux Kernel Mailing List , ACPI Devel Maling List On Tuesday, September 08, 2015 12:40:08 PM Peter Zijlstra wrote: > 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&m4109156901959&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. OK, I'll try to get that later this week. Or maybe Jiang Liu can beat me to doing that. :-) Thanks, Rafael