From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [RFD driver-core] Lifetime problems of the current driver model Date: Sat, 31 Mar 2007 12:12:48 +0900 Message-ID: <460DD1B0.4080605@gmail.com> References: <460CDBA6.5030608@gmail.com> <20070330151926.18fc12a0@gondolin.boeblingen.de.ibm.com> <460D0E78.3040200@gmail.com> <20070330154042.4c7deb72@gondolin.boeblingen.de.ibm.com> <460D178F.4000500@gmail.com> <20070330165251.7beffc7c@gondolin.boeblingen.de.ibm.com> <460D27E3.2050602@gmail.com> <20070330213101.7aa7babf@gondolin.boeblingen.de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from wr-out-0506.google.com ([64.233.184.231]:22725 "EHLO wr-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933559AbXCaDM4 (ORCPT ); Fri, 30 Mar 2007 23:12:56 -0400 Received: by wr-out-0506.google.com with SMTP id 76so904640wra for ; Fri, 30 Mar 2007 20:12:55 -0700 (PDT) In-Reply-To: <20070330213101.7aa7babf@gondolin.boeblingen.de.ibm.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Cornelia Huck Cc: gregkh@suse.de, hugh@veritas.com, dmitry.torokhov@gmail.com, oneukum@suse.de, maneesh@in.ibm.com, rpurdie@rpsys.net, James.Bottomley@SteelEye.com, Jeff Garzik , lkml , "linux-ide@vger.kernel.org" , SCSI Mailing List Cornelia Huck wrote: > On Sat, 31 Mar 2007 00:08:19 +0900, > Tejun Heo wrote: > >> (3) make sure all existing kobjects are released by module exit function. >> >> For example, let's say there is a hypothetical disk device /dev/dk0 >> driven by a hypothetical driver mydrv. /dev/dk0 is represented like the >> following in the sysfs tree. >> >> /sys/devices/pci0000:00/0000:00:1f.0/dk0/{myknob0,myknob1} >> >> Owner of both attrs myknob0 and myknob1 is mydrv and opening either >> increases the reference counts of dk0 and mydrv and closing does the >> opposite. >> >> * When there is no opener of either knob and the /dev/dk0 isn't used by >> anyone. Reference count of dk0 is 1, mydrv 0. > > Hm, but as long as dk0 is registered, it can be looked up and someone > could get a reference on it. Yeah, exactly. That's why any getting any kobject reference backed by a module must be accompanied by try_module_get(). int mydrv_get_dk(struct dk *dk) { rc = try_module_get(mydrv); if (rc) return rc; kobject_get(&dk->kobj); return 0; } >> * User issues rmmod mydrv. As mydrv's reference count is zero, unload >> proceeds and mydrv's exit function is called. >> >> * mydrv's exit function looks like the following. >> >> mydrv_exit() >> { >> sysfs_remove_file(dk0, myknob0); >> sysfs_remove_file(dk1, myknob1); >> device_del(dk0); >> deinit controller; >> release all resources; >> } >> >> The device_del(dk0) drops dk0's reference count to zero and its >> ->release is invoked immediately. > > And here is the problem if someone else still has a reference. The > module will be unloaded, but ->release will not be called until the > "someone else" gives up the reference... Exactly, in that case, module reference count must not be zero. You and I are saying the same thing. Why are we running in circle? -- tejun