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Mon, 18 May 2026 20:39:30 -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 08/24] iommu: Change group->devices to RCU-protected list Date: Mon, 18 May 2026 20:38:51 -0700 Message-ID: <5eee6cadabf8976eb3abe03306eaf0bc5d9d73ec.1779161849.git.nicolinc@nvidia.com> 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: DS2PEPF000061C8:EE_|BN7PPF0FD1DEA27:EE_ X-MS-Office365-Filtering-Correlation-Id: dac03f84-7b69-4d0c-535c-08deb55845ed X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|1800799024|376014|82310400026|7416014|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)(36860700016)(1800799024)(376014)(82310400026)(7416014)(18002099003)(22082099003)(56012099003)(11063799003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 4wqwFOYjVOuqnjmplkOOHNTpkzCgYDw2KFPT1D6q5HPLKwHfsevxpZpJ5TVBrjb2HHyOr2opFRe3mVdK2S0HJerZYsn3fxrlGPDkV4IWyw+Z5FBNSB9cwiKC9ASQj4NWVShOaL30yeiOBiZDEiwmUWuGsMfp4O/ikhs6KLihs0w1rsAGa1dtM2tbbJ4ECA/QBHJaqGCHS991kvBi3csS/rENNQoovRt3smfKA//AOSLeunYM6WWoV+tgv60ggnz72dlWG6zmVVAESeBmJwqxynMFY6VClcuN4YUCZCx6WUEpef4yhc9jqssp50BPV4GF9mhCbO2VdhPe9xapFDIbGCtE2tth40EMIqnfZ46splIJjMr5qCzBmVr8lLyBJnKFnA+FYkv6N1qXNP80ce18TGKzEhmZEFVFlhR0s9rA5QzNmxWhSov09PlPlUvdkckw X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 May 2026 03:39:46.6495 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: dac03f84-7b69-4d0c-535c-08deb55845ed 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: DS2PEPF000061C8.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN7PPF0FD1DEA27 To allow lockless iterations of the group->devices list in an ISR context that cannot hold the group->mutex, change the list to be RCU protected. Mark the existing __dev_to_gdev() for group->mutex case only. A subsequent change will add another __dev_to_gdev_rcu() for RCU case. Hold grp_dev->dev across the RCU grace period using synchronize_rcu(), in __iommu_group_free_device(). Without that, the driver core might free the struct device while an RCU reader is still mid-iteration. Note: a call_rcu() callback runs in softirq context, but put_device() may sleep -- the device release path can invoke devres_release_all() and ->release callbacks that take mutexes. Use synchronize_rcu() to defer the put_device() to the (sleepable) caller context instead. Note that in bus_iommu_probe() there is a for_each_group_device marked as FIXME, which can't take either mutex or RCU read lock. Plainly replace it with list_for_each_entry for a status quo. Signed-off-by: Nicolin Chen --- drivers/iommu/iommu.c | 25 ++++++++++++++++++------- 1 file changed, 18 insertions(+), 7 deletions(-) diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c index 2f8f3ea13f490..4116b28258bde 100644 --- a/drivers/iommu/iommu.c +++ b/drivers/iommu/iommu.c @@ -97,8 +97,10 @@ struct group_device { /* Iterate over each struct group_device in a struct iommu_group */ #define for_each_group_device(group, pos) \ - list_for_each_entry(pos, &(group)->devices, list) + list_for_each_entry_rcu(pos, &(group)->devices, list, \ + lockdep_is_held(&(group)->mutex)) +/* Caller must hold dev->iommu_group->mutex. */ static struct group_device *__dev_to_gdev(struct device *dev) { struct iommu_group *group = dev->iommu_group; @@ -688,7 +690,7 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list * The gdev must be in the list before calling * iommu_setup_default_domain() */ - list_add_tail(&gdev->list, &group->devices); + list_add_tail_rcu(&gdev->list, &group->devices); WARN_ON(group->default_domain && !group->domain); if (group->default_domain) iommu_create_device_direct_mappings(group->default_domain, dev); @@ -719,7 +721,7 @@ static int __iommu_probe_device(struct device *dev, struct list_head *group_list return 0; err_remove_gdev: - list_del(&gdev->list); + list_del_rcu(&gdev->list); __iommu_group_empty_assert_owner_cnt(group); err_put_group: iommu_deinit_device(dev); @@ -762,6 +764,10 @@ static void __iommu_group_free_device(struct iommu_group *group, trace_remove_device_from_group(group->id, dev); kfree(grp_dev->name); + + /* Wait for any in-flight reader to drop the reference to gdev->dev */ + synchronize_rcu(); + put_device(grp_dev->dev); kfree(grp_dev); } @@ -779,7 +785,7 @@ static void __iommu_group_remove_device(struct device *dev) /* Must drop the recovery_cnt when removing a blocked device */ if (device->blocked && !WARN_ON(group->recovery_cnt == 0)) group->recovery_cnt--; - list_del(&device->list); + list_del_rcu(&device->list); __iommu_group_empty_assert_owner_cnt(group); if (dev_has_iommu(dev)) iommu_deinit_device(dev); @@ -1298,6 +1304,8 @@ static struct group_device *iommu_group_alloc_device(struct iommu_group *group, return ERR_PTR(-ENOMEM); device->dev = dev; + /* Keep dev alive for any in-flight RCU reader of grp_dev->dev. */ + get_device(dev); ret = sysfs_create_link(&dev->kobj, &group->kobj, "iommu_group"); if (ret) @@ -1337,6 +1345,7 @@ static struct group_device *iommu_group_alloc_device(struct iommu_group *group, err_remove_link: sysfs_remove_link(&dev->kobj, "iommu_group"); err_free_device: + put_device(dev); kfree(device); dev_err(dev, "Failed to add to iommu group %d: %d\n", group->id, ret); return ERR_PTR(ret); @@ -1362,7 +1371,7 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev) rcu_assign_pointer(dev_iommu_group_rcu(dev), group); mutex_lock(&group->mutex); - list_add_tail(&gdev->list, &group->devices); + list_add_tail_rcu(&gdev->list, &group->devices); mutex_unlock(&group->mutex); return 0; } @@ -2011,9 +2020,11 @@ static int bus_iommu_probe(const struct bus_type *bus) * FIXME: Mis-locked because the ops->probe_finalize() call-back * of some IOMMU drivers calls arm_iommu_attach_device() which * in-turn might call back into IOMMU core code, where it tries - * to take group->mutex, resulting in a deadlock. + * to take group->mutex, resulting in a deadlock. Unfortunately, + * as iommu_group_do_probe_finalize() can sleep, rcu_read_lock() + * cannot be held to mitigate this. */ - for_each_group_device(group, gdev) + list_for_each_entry(gdev, &group->devices, list) iommu_group_do_probe_finalize(gdev->dev); } -- 2.43.0