From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Roedel Subject: Re: [PATCH 1/2] iommu/s390: Fix IOMMU groups Date: Fri, 28 Apr 2017 16:40:30 +0200 Message-ID: <20170428144030.GG1332@8bytes.org> References: <1493306905-32334-1-git-send-email-joro@8bytes.org> <1493306905-32334-2-git-send-email-joro@8bytes.org> <20170427201142.18d467a3@thinkpad> <20170427211232.GF1332@8bytes.org> <20170428152017.5e99d67f@thinkpad> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20170428152017.5e99d67f@thinkpad> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Gerald Schaefer Cc: iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, Joerg Roedel , Sebastian Ott , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: iommu@lists.linux-foundation.org On Fri, Apr 28, 2017 at 03:20:17PM +0200, Gerald Schaefer wrote: > On Thu, 27 Apr 2017 23:12:32 +0200 > Joerg Roedel wrote: > > This is the way to free an iommu-group. It was missing before probably > > because it was unclear whether the add_device function allocated a group > > or not. So there was no way to know if it needs to be put again in the > > remove_device function. > > Hmm, for the reference count it should not matter whether a new group was > allocated or an existing group found with iommu_group_get(). Our add_device > callback always gets one reference either from iommu_group_get or _alloc, > and then another one from iommu_group_add_device(), after which the first > reference is put again. So there should always be one reference more after > a successful add_device. Right, my statement above is wrong. The current code is fine, it gets a reference to the group with iommu_group_get/iommu_group_alloc, attaches the device to the group (which takes a reference to the group of its own), and in the end it drops its local reference. When the device->group link is broken up in the remove_device function, that reference is also dropped. So everything is fine. The additional iommu_group_put() in my patch is wrong. Regards, Joerg