Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752036AbaDYN74 (ORCPT ); Fri, 25 Apr 2014 09:59:56 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:42515 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751184AbaDYN7y (ORCPT ); Fri, 25 Apr 2014 09:59:54 -0400 Date: Fri, 25 Apr 2014 09:59:53 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Li Zhong cc: Johan Hovold , Tejun Heo , Greg Kroah-Hartman , , , Subject: Re: [PATCH] USB: serial: fix sysfs-attribute removal deadlock In-Reply-To: <1398392217.2805.150.camel@ThinkPad-T5421.cn.ibm.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 25 Apr 2014, Li Zhong wrote: > > No, this isn't self removal. The driver-attribute (not device-attribute) > > store operation simply grabs a lock that is also held while the driver > > is being deregistered at module unload. Taking a reference to the module > > in this case will prevent deregistration while store is running. > > > > But it seems like this can be solved for usb-serial by simply not > > holding the lock while deregistering. > > I didn't look carefully about this lock. > > But I'm not sure whether there are such requirements for driver > attributes: > > some lock needs be grabbed in the driver attributes store callbacks, and > the same lock also needs to be grabbed during driver unregister. In this case, the lock does _not_ need to be grabbed during driver unregister. The driver grabs the lock, but it doesn't need to. > If we have such requirements currently or in the future, I think they > could all be solved by breaking active protection after get the module > reference. No! That would be very bad. Unloading modules is quite different from unbinding drivers. After the driver is unbound, its attribute callback routines can continue to run. But after a driver module has been unloaded, its attribute callback routines _cannot_ run because they aren't present in memory any more. If we allowed a module to be unloaded while one of its callbacks was running (because active protection was broken), imagine what would happen... Alan Stern -- 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/