Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752378AbaDYPN5 (ORCPT ); Fri, 25 Apr 2014 11:13:57 -0400 Received: from mail-la0-f42.google.com ([209.85.215.42]:58980 "EHLO mail-la0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751422AbaDYPNz (ORCPT ); Fri, 25 Apr 2014 11:13:55 -0400 Date: Fri, 25 Apr 2014 17:13:27 +0200 From: Johan Hovold To: Alan Stern Cc: Li Zhong , Tejun Heo , Johan Hovold , Greg Kroah-Hartman , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com Subject: Re: [PATCH] USB: serial: fix sysfs-attribute removal deadlock Message-ID: <20140425151327.GF2206@localhost> References: <1398392134.2805.149.camel@ThinkPad-T5421.cn.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.22 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 25, 2014 at 09:54:33AM -0400, Alan Stern wrote: > On Fri, 25 Apr 2014, Li Zhong wrote: > > > > I don't get why try_module_get() matters here. We can't call into > > > ->store if the object at hand is already destroyed and the underlying > > > module can't go away if the target device is still alive. > > > try_module_get() doesn't actually protect the object. Why does that > > > matter? This is self removal, right? Can you please take a look at > > > kernfs_remove_self()? > > > > This is about one process writing something to driver attributes, and > > one process trying to unload this driver. > > > > I think try_module_get() could detect whether the driver is being > > unloaded, and if not, prevent it from being unloaded, so it could > > protect the object here by not allow the driver to be unloaded. > > That isn't how try_module_get() works. If the module is being > unloaded, try_module_get() simply fails. It does not prevent the > module from being unloaded -- that's why its name begins with "try". Well, to be fair, if the try_module_get() *succeeds* it will prevent the module from being unloaded (and otherwise the sysfs operation bails out). Johan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/