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Tue, 17 May 2022 07:55:25 GMT From: Alexander A Sverdlin To: linux-i2c@vger.kernel.org Cc: Alexander Sverdlin , Wolfram Sang , linux-kernel@vger.kernel.org Subject: [PATCH] i2c: core: Workaround false-positive LOCKDEP in delete_device Date: Tue, 17 May 2022 09:55:18 +0200 Message-Id: <20220517075518.43613-1-alexander.sverdlin@nokia.com> X-Mailer: git-send-email 2.10.2 X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email MIME-Version: 1.0 Content-Type: text/plain X-MS-Office365-Filtering-Correlation-Id: f8bc34c1-c158-4ce2-4fd1-08da37da9acc X-MS-TrafficTypeDiagnostic: HE1PR0702MB3547:EE_ X-Microsoft-Antispam-PRVS: X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:131.228.2.8;CTRY:FI;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:fihe3nok0734.emea.nsn-net.net;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230001)(4636009)(36840700001)(46966006)(40470700004)(82310400005)(40460700003)(36860700001)(54906003)(356005)(6666004)(186003)(81166007)(316002)(6916009)(8936002)(5660300002)(508600001)(70206006)(70586007)(26005)(82960400001)(2906002)(36756003)(83380400001)(86362001)(336012)(2616005)(4326008)(47076005)(8676002)(1076003)(36900700001);DIR:OUT;SFP:1102; X-OriginatorOrg: nokia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 May 2022 07:55:26.5044 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f8bc34c1-c158-4ce2-4fd1-08da37da9acc X-MS-Exchange-CrossTenant-Id: 5d471751-9675-428d-917b-70f44f9630b0 X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=5d471751-9675-428d-917b-70f44f9630b0;Ip=[131.228.2.8];Helo=[fihe3nok0734.emea.nsn-net.net] X-MS-Exchange-CrossTenant-AuthSource: VE1EUR03FT045.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: HE1PR0702MB3547 X-Spam-Status: No, score=-1.2 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,FORGED_SPF_HELO,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE,T_SCC_BODY_TEXT_LINE autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Alexander Sverdlin Drop the mutex earlier in the loop so that LOCKDEP is not being provoked: WARNING: possible circular locking dependency detected .../9201 is trying to acquire lock: ffffff85656d4e78 (kn->count#159){++++}, at: kernfs_remove_by_name_ns+0x5c/0xac but task is already holding lock: ffffff857b329e80 (&adap->userspace_clients_lock){+.+.}, at: i2c_sysfs_delete_device+0x8c/0x1f0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&adap->userspace_clients_lock){+.+.}: __mutex_lock+0xa4/0x924 mutex_lock_nested+0x48/0x5c i2c_sysfs_new_device+0x108/0x220 dev_attr_store+0x48/0x60 sysfs_kf_write+0x54/0x80 kernfs_fop_write+0x120/0x240 __vfs_write+0x4c/0x90 vfs_write+0xe8/0x1d0 ksys_write+0x7c/0x104 __arm64_sys_write+0x28/0x3c el0_svc_handler+0x90/0x200 el0_svc+0x8/0x16c -> #0 (kn->count#159){++++}: __lock_acquire+0xe8c/0x1a90 lock_acquire+0xd8/0x270 __kernfs_remove+0x2fc/0x360 kernfs_remove_by_name_ns+0x5c/0xac remove_files+0x48/0x90 sysfs_remove_group+0x50/0xa0 sysfs_remove_groups+0x44/0x60 device_remove_attrs+0x60/0x80 device_del+0x134/0x360 device_unregister+0x28/0x80 i2c_del_adapter+0x210/0x2a4 i2c_mux_del_adapters+0xa4/0xfc pca9641_remove+0x24/0x34 [i2c_mux_pca9641] i2c_device_remove+0x60/0xd4 __device_release_driver+0x164/0x1f4 device_release_driver+0x38/0x4c bus_remove_device+0xe0/0x15c device_del+0x13c/0x360 device_unregister+0x28/0x80 i2c_unregister_device+0x5c/0x70 i2c_sysfs_delete_device+0x1b8/0x1f0 dev_attr_store+0x48/0x60 sysfs_kf_write+0x54/0x80 kernfs_fop_write+0x120/0x240 __vfs_write+0x4c/0x90 vfs_write+0xe8/0x1d0 ksys_write+0x7c/0x104 __arm64_sys_write+0x28/0x3c el0_svc_handler+0x90/0x200 el0_svc+0x8/0x16c other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&adap->userspace_clients_lock); lock(kn->count#159); lock(&adap->userspace_clients_lock); lock(kn->count#159); *** DEADLOCK *** 5 locks held by .../9201: #0: ffffff83f29c3ce0 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0x74/0xe0 #1: ffffff857a2f0410 (sb_writers#4){.+.+}, at: vfs_write+0x174/0x1d0 #2: ffffff856bbbe680 (&of->mutex){+.+.}, at: kernfs_fop_write+0xf0/0x240 #3: ffffff857b329e80 (&adap->userspace_clients_lock){+.+.}, at: i2c_sysfs_delete_device+0x8c/0x1f0 #4: ffffff83f134ad80 (&dev->mutex){....}, at: device_release_driver+0x2c/0x4c stack backtrace: Call trace: dump_backtrace+0x0/0x180 show_stack+0x28/0x3c dump_stack+0xf4/0x150 print_circular_bug+0x21c/0x22c check_noncircular+0x15c/0x1e0 __lock_acquire+0xe8c/0x1a90 lock_acquire+0xd8/0x270 __kernfs_remove+0x2fc/0x360 kernfs_remove_by_name_ns+0x5c/0xac remove_files+0x48/0x90 sysfs_remove_group+0x50/0xa0 sysfs_remove_groups+0x44/0x60 device_remove_attrs+0x60/0x80 device_del+0x134/0x360 device_unregister+0x28/0x80 i2c_del_adapter+0x210/0x2a4 i2c_mux_del_adapters+0xa4/0xfc pca9641_remove+0x24/0x34 [i2c_mux_pca9641] i2c_device_remove+0x60/0xd4 __device_release_driver+0x164/0x1f4 device_release_driver+0x38/0x4c bus_remove_device+0xe0/0x15c device_del+0x13c/0x360 device_unregister+0x28/0x80 i2c_unregister_device+0x5c/0x70 i2c_sysfs_delete_device+0x1b8/0x1f0 dev_attr_store+0x48/0x60 sysfs_kf_write+0x54/0x80 kernfs_fop_write+0x120/0x240 __vfs_write+0x4c/0x90 vfs_write+0xe8/0x1d0 ksys_write+0x7c/0x104 __arm64_sys_write+0x28/0x3c el0_svc_handler+0x90/0x200 el0_svc+0x8/0x16c Signed-off-by: Alexander Sverdlin --- drivers/i2c/i2c-core-base.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c index d43db2c..bd2e3e4 100644 --- a/drivers/i2c/i2c-core-base.c +++ b/drivers/i2c/i2c-core-base.c @@ -1272,9 +1272,14 @@ delete_device_store(struct device *dev, struct device_attribute *attr, "delete_device", client->name, client->addr); list_del(&client->detected); + /* + * We drop the mutex here, because device unregister + * will take sysfs lock (kn->count) which, as LOCKDEP + * would think, depends on this mutex + */ + mutex_unlock(&adap->userspace_clients_lock); i2c_unregister_device(client); - res = count; - break; + return count; } } mutex_unlock(&adap->userspace_clients_lock); -- 2.10.2