From 621e55ff5b8e0ab5d1063f0eae0ef3960bef8f6e Mon Sep 17 00:00:00 2001 From: Jason Gunthorpe Date: Wed, 31 Jul 2019 11:18:40 +0300 Subject: [PATCH] RDMA/devices: Do not deadlock during client removal lockdep reports: WARNING: possible circular locking dependency detected modprobe/302 is trying to acquire lock: 0000000007c8919c ((wq_completion)ib_cm){+.+.}, at: flush_workqueue+0xdf/0x990 but task is already holding lock: 000000002d3d2ca9 (&device->client_data_rwsem){++++}, at: remove_client_context+0x79/0xd0 [ib_core] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&device->client_data_rwsem){++++}: down_read+0x3f/0x160 ib_get_net_dev_by_params+0xd5/0x200 [ib_core] cma_ib_req_handler+0x5f6/0x2090 [rdma_cm] cm_process_work+0x29/0x110 [ib_cm] cm_req_handler+0x10f5/0x1c00 [ib_cm] cm_work_handler+0x54c/0x311d [ib_cm] process_one_work+0x4aa/0xa30 worker_thread+0x62/0x5b0 kthread+0x1ca/0x1f0 ret_from_fork+0x24/0x30 -> #1 ((work_completion)(&(&work->work)->work)){+.+.}: process_one_work+0x45f/0xa30 worker_thread+0x62/0x5b0 kthread+0x1ca/0x1f0 ret_from_fork+0x24/0x30 -> #0 ((wq_completion)ib_cm){+.+.}: lock_acquire+0xc8/0x1d0 flush_workqueue+0x102/0x990 cm_remove_one+0x30e/0x3c0 [ib_cm] remove_client_context+0x94/0xd0 [ib_core] disable_device+0x10a/0x1f0 [ib_core] __ib_unregister_device+0x5a/0xe0 [ib_core] ib_unregister_device+0x21/0x30 [ib_core] mlx5_ib_stage_ib_reg_cleanup+0x9/0x10 [mlx5_ib] __mlx5_ib_remove+0x3d/0x70 [mlx5_ib] mlx5_ib_remove+0x12e/0x140 [mlx5_ib] mlx5_remove_device+0x144/0x150 [mlx5_core] mlx5_unregister_interface+0x3f/0xf0 [mlx5_core] mlx5_ib_cleanup+0x10/0x3a [mlx5_ib] __x64_sys_delete_module+0x227/0x350 do_syscall_64+0xc3/0x6a4 entry_SYSCALL_64_after_hwframe+0x49/0xbe Which is due to the read side of the client_data_rwsem being obtained recursively through a work queue flush during cm client removal. The lock is being held across the remove in remove_client_context() so that the function is a fence, once it returns the client is removed. This is required so that the two callers do not proceed with destruction until the client completes removal. Instead of using client_data_rwsem use the existing device unregistration refcount and add a similar client unregistration (client->uses) refcount. This will fence the two unregistration paths without holding any locks. Cc: Fixes: 921eab1143aa ("RDMA/devices: Re-organize device.c locking") Signed-off-by: Jason Gunthorpe Signed-off-by: Leon Romanovsky Link: https://lore.kernel.org/r/20190731081841.32345-2-leon@kernel.org Signed-off-by: Doug Ledford --- drivers/infiniband/core/device.c | 56 ++++++++++++++++++++++++-------- include/rdma/ib_verbs.h | 3 ++ 2 files changed, 45 insertions(+), 14 deletions(-) diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c index 9773145dee09..d86fbabe48d6 100644 --- a/drivers/infiniband/core/device.c +++ b/drivers/infiniband/core/device.c @@ -99,6 +99,12 @@ static LIST_HEAD(client_list); static DEFINE_XARRAY_FLAGS(clients, XA_FLAGS_ALLOC); static DECLARE_RWSEM(clients_rwsem); +static void ib_client_put(struct ib_client *client) +{ + if (refcount_dec_and_test(&client->uses)) + complete(&client->uses_zero); +} + /* * If client_data is registered then the corresponding client must also still * be registered. @@ -660,6 +666,14 @@ static int add_client_context(struct ib_device *device, return 0; down_write(&device->client_data_rwsem); + /* + * So long as the client is registered hold both the client and device + * unregistration locks. + */ + if (!refcount_inc_not_zero(&client->uses)) + goto out_unlock; + refcount_inc(&device->refcount); + /* * Another caller to add_client_context got here first and has already * completely initialized context. @@ -683,6 +697,9 @@ static int add_client_context(struct ib_device *device, return 0; out: + ib_device_put(device); + ib_client_put(client); +out_unlock: up_write(&device->client_data_rwsem); return ret; } @@ -702,7 +719,7 @@ static void remove_client_context(struct ib_device *device, client_data = xa_load(&device->client_data, client_id); xa_clear_mark(&device->client_data, client_id, CLIENT_DATA_REGISTERED); client = xa_load(&clients, client_id); - downgrade_write(&device->client_data_rwsem); + up_write(&device->client_data_rwsem); /* * Notice we cannot be holding any exclusive locks when calling the @@ -712,17 +729,13 @@ static void remove_client_context(struct ib_device *device, * * For this reason clients and drivers should not call the * unregistration functions will holdling any locks. - * - * It tempting to drop the client_data_rwsem too, but this is required - * to ensure that unregister_client does not return until all clients - * are completely unregistered, which is required to avoid module - * unloading races. */ if (client->remove) client->remove(device, client_data); xa_erase(&device->client_data, client_id); - up_read(&device->client_data_rwsem); + ib_device_put(device); + ib_client_put(client); } static int alloc_port_data(struct ib_device *device) @@ -1705,6 +1718,8 @@ int ib_register_client(struct ib_client *client) unsigned long index; int ret; + refcount_set(&client->uses, 1); + init_completion(&client->uses_zero); ret = assign_client_id(client); if (ret) return ret; @@ -1740,16 +1755,29 @@ void ib_unregister_client(struct ib_client *client) unsigned long index; down_write(&clients_rwsem); + ib_client_put(client); xa_clear_mark(&clients, client->client_id, CLIENT_REGISTERED); up_write(&clients_rwsem); - /* - * Every device still known must be serialized to make sure we are - * done with the client callbacks before we return. - */ - down_read(&devices_rwsem); - xa_for_each (&devices, index, device) + + /* We do not want to have locks while calling client->remove() */ + rcu_read_lock(); + xa_for_each (&devices, index, device) { + if (!ib_device_try_get(device)) + continue; + rcu_read_unlock(); + remove_client_context(device, client->client_id); - up_read(&devices_rwsem); + + ib_device_put(device); + rcu_read_lock(); + } + rcu_read_unlock(); + + /* + * remove_client_context() is not a fence, it can return even though a + * removal is ongoing. Wait until all removals are completed. + */ + wait_for_completion(&client->uses_zero); down_write(&clients_rwsem); list_del(&client->list); diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h index c5f8a9f17063..7b80ec822043 100644 --- a/include/rdma/ib_verbs.h +++ b/include/rdma/ib_verbs.h @@ -2647,6 +2647,9 @@ struct ib_client { const union ib_gid *gid, const struct sockaddr *addr, void *client_data); + + refcount_t uses; + struct completion uses_zero; struct list_head list; u32 client_id;