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Mon, 18 May 2026 20:39:28 -0700 From: Nicolin Chen To: Will Deacon , Robin Murphy , "Joerg Roedel" , Bjorn Helgaas , "Jason Gunthorpe" CC: "Rafael J . Wysocki" , Len Brown , Pranjal Shrivastava , Mostafa Saleh , Lu Baolu , Kevin Tian , , , , , , , Shuai Xue Subject: [PATCH v4 06/24] iommu: Defer iommu_group free via kfree_rcu() Date: Mon, 18 May 2026 20:38:49 -0700 Message-ID: X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF000061C3:EE_|CH3PR12MB8210:EE_ X-MS-Office365-Filtering-Correlation-Id: 9244b3e8-542d-4e3a-7e9d-08deb558446c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|36860700016|1800799024|82310400026|18002099003|22082099003|56012099003|11063799003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:216.228.117.161;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge2.nvidia.com;CAT:NONE;SFS:(13230040)(376014)(7416014)(36860700016)(1800799024)(82310400026)(18002099003)(22082099003)(56012099003)(11063799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: elS+npFLbi9AFYb8StXOLGM4q4lGAOj2ItY4j/o+6WkZ86S0hh2jDkpOVOWuCgxWsmjZLraYnTVD3a1+GPjCQr+ANg9czTydwk4f2Q6fN5izKZs3Ti6vb1sGIWva0A27LUlLLes7zhm2wr4D/CsRaVWkRYhxBYX2EarZgWYuQNB9omhg02ZVql/zudZ+HhZsqimh4L/1mp7mBFL4lYJVk0QDzxJgJ5Le5JyqiqshCsYnA6UiUchuoCaRUdCGLFBwlcpKsL54v4pmuPROEhRv32eiP+JRHGyIdA+FXTccaVtq7EahqvlRFYGXzPf0upkktbKmZq+dEo407SKyIgneYM+DMoNYX0ksnejUxJOeLJt40RPfmRZC9GLxN0ZUmrSjbnCMCERv0LLk7YqVgrXCFazwWBRKaRajLOc2M5Fgih347/0WG2cysWdLCv64ZsuZ X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 May 2026 03:39:44.1320 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9244b3e8-542d-4e3a-7e9d-08deb558446c X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.161];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DS2PEPF000061C3.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR12MB8210 dev->iommu_group will be read in an ISR-context to look up a group_device for fault reporting, in which case mutex cannot be used. For that read to be safe, two things are needed: (1) The iommu_group memory that dev->iommu_group points to must outlive any in-flight rcu_read_lock section. Add rcu_head to iommu_group and switch iommu_group_release() to calling kfree_rcu(). (2) The publication of dev->iommu_group must pair with rcu_dereference() at the upcoming reader (cannot hold mutex but rcu_read_lock), so the writers must use rcu_assign_pointer(). Existing readers do not use rcu_dereference(); they retain their current synchronization model. Apply a __rcu __force cast at the writer sites to satisfy sparse without forcing every reader to convert. New reader added by the subsequent change uses rcu_dereference() only, to reach group->devices for a list lookup. And it does not touch group->name and other fields. The kfree_rcu() here is supposed to keep group->devices alive across the read-side critical section; other fields will not affect the reader. Note: this change alone does not yet make group->devices iteration safe under rcu_read_lock(); a subsequent change will convert the group_device list to RCU and switch struct group_device to kfree_rcu(). Assisted-by: Claude:claude-opus-4-7 Signed-off-by: Nicolin Chen --- drivers/iommu/iommu.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index e68c7b142ad5a..6727b6f7797bd 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -71,8 +71,12 @@ struct iommu_group { */ unsigned int recovery_cnt; void *owner; + struct rcu_head rcu; }; +#define dev_iommu_group_rcu(dev) \ + (*((struct iommu_group __rcu __force **)&(dev)->iommu_group)) + enum gdev_blocked { BLOCKED_NO = 0, /* Not blocked */ BLOCKED_RESETTING, /* PCI reset in flight */ @@ -531,7 +535,7 @@ static int iommu_init_device(struct device *dev) ret = PTR_ERR(group); goto err_unlink; } - dev->iommu_group = group; + rcu_assign_pointer(dev_iommu_group_rcu(dev), group); dev->iommu->max_pasids = dev_iommu_get_max_pasids(dev); if (ops->is_attach_deferred) @@ -613,7 +617,7 @@ static void iommu_deinit_device(struct device *dev) } /* Caller must put iommu_group */ - dev->iommu_group = NULL; + rcu_assign_pointer(dev_iommu_group_rcu(dev), NULL); module_put(ops->owner); dev_iommu_free(dev); #ifdef CONFIG_IOMMU_DMA @@ -772,7 +776,7 @@ static void __iommu_group_remove_device(struct device *dev) if (dev_has_iommu(dev)) iommu_deinit_device(dev); else - dev->iommu_group = NULL; + rcu_assign_pointer(dev_iommu_group_rcu(dev), NULL); break; } mutex_unlock(&group->mutex); @@ -1059,7 +1063,7 @@ static void iommu_group_release(struct kobject *kobj) WARN_ON(group->blocking_domain); kfree(group->name); - kfree(group); + kfree_rcu(group, rcu); } static const struct kobj_type iommu_group_ktype = { @@ -1344,7 +1348,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev) return PTR_ERR(gdev); iommu_group_ref_get(group); - dev->iommu_group = group; + rcu_assign_pointer(dev_iommu_group_rcu(dev), group); mutex_lock(&group->mutex); list_add_tail(&gdev->list, &group->devices); -- 2.43.0