Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752208AbbKINd1 (ORCPT ); Mon, 9 Nov 2015 08:33:27 -0500 Received: from mail-pa0-f50.google.com ([209.85.220.50]:36278 "EHLO mail-pa0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752157AbbKINdZ (ORCPT ); Mon, 9 Nov 2015 08:33:25 -0500 Date: Mon, 9 Nov 2015 21:30:14 +0800 From: Peng Fan To: Will Deacon Cc: joro@8bytes.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [RFC V2] iommu: correct group reference count Message-ID: <20151109133011.GA16563@linux-jyl1.ap.freescale.net> References: <1447049608-6123-1-git-send-email-van.freenix@gmail.com> <20151109101058.GB24936@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151109101058.GB24936@arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3301 Lines: 100 Hi Will, On Mon, Nov 09, 2015 at 10:10:59AM +0000, Will Deacon wrote: >On Mon, Nov 09, 2015 at 02:13:28PM +0800, Peng Fan wrote: >> The basic flow for iommu_group_for_dev is: >> iommu_group_get_for_dev >> |-> iommu_group_get : increase reference count by 1. >> return group; >> |-> ops->device_group : Init/increase reference count to/by 1. >> iommu_group_add_device : Increase reference count by 1. >> return group; >> >> We can see that ops->device_group and iommu_group_add_device will together >> increase the iommu group reference count by 2. Actually we only need 1, >> but not 2. So we need add iommu_group_put after iommu_group_add_device >> to make sure iommu_group_get_for_dev only increase reference count by 1. >> >> Signed-off-by: Peng Fan >> Cc: Joerg Roedel >> Cc: Will Deacon >> --- >> >> V1 thread: https://lkml.org/lkml/2015/11/3/304 >> Changes V2: >> I did not see the update about device_group when I worked out V1. So >> redo the patch and refine commit msg and rebased to latest linus' >> linux master tree. >> >> drivers/iommu/iommu.c | 6 +++--- >> 1 file changed, 3 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >> index abae363..9c1971b 100644 >> --- a/drivers/iommu/iommu.c >> +++ b/drivers/iommu/iommu.c >> @@ -852,10 +852,10 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev) >> } >> >> ret = iommu_group_add_device(group, dev); >> - if (ret) { >> - iommu_group_put(group); >> + iommu_group_put(group); >> + >> + if (ret) >> return ERR_PTR(ret); >> - } > >Hmm, I don't think this is correct either: > > (1) It doesn't help the arm-smmu driver (which deals with platform > devices too) > > (2) It breaks IOMMU drivers that currently have the explicit put already > (e.g. amd-iommu.c:init_iommu_group) > >The easiest way for you to proceed is to extend your original patch so >that it also adds an iommu_group_put to the arm-smmu-v3 driver after >a successful iommu_group_get_for_dev. I am not sure if the following patch is what you preferred. But this means that iommu_grou_get_for_dev will increase the group reference count by 2, when need to create a new group? diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c index 4e5118a..9c88301 100644 --- a/drivers/iommu/arm-smmu-v3.c +++ b/drivers/iommu/arm-smmu-v3.c @@ -1855,6 +1855,9 @@ static int arm_smmu_add_device(struct device *dev) /* Add the new SID */ sids[smmu_group->num_sids - 1] = sid; smmu_group->sids = sids; + + iommu_group_put(group); + return 0; out_put_group: diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c index 47dc7a7..af6afce 100644 --- a/drivers/iommu/arm-smmu.c +++ b/drivers/iommu/arm-smmu.c @@ -1357,6 +1357,8 @@ static int arm_smmu_add_device(struct device *dev) if (IS_ERR(group)) return PTR_ERR(group); + iommu_group_put(group); + return 0; } Thanks, Peng. > >Will -- 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/