From ea819867b788728aca60717e4fdacb3df771f670 Mon Sep 17 00:00:00 2001 From: Zach Brown Date: Thu, 15 Jul 2010 12:34:33 -0700 Subject: RDS/IB: protect the list of IB devices The RDS IB device list wasn't protected by any locking. Traversal in both the get_mr and FMR flushing paths could race with additon and removal. List manipulation is done with RCU primatives and is protected by the write side of a rwsem. The list traversal in the get_mr fast path is protected by a rcu read critical section. The FMR list traversal is more problematic because it can block while traversing the list. We protect this with the read side of the rwsem. Signed-off-by: Zach Brown --- net/rds/ib.c | 27 ++++++++++++++++++++------- 1 file changed, 20 insertions(+), 7 deletions(-) (limited to 'net/rds/ib.c') diff --git a/net/rds/ib.c b/net/rds/ib.c index 3eb5617649c6..b12a3951167d 100644 --- a/net/rds/ib.c +++ b/net/rds/ib.c @@ -53,6 +53,12 @@ MODULE_PARM_DESC(fmr_message_size, " Max size of a RDMA transfer"); module_param(rds_ib_retry_count, int, 0444); MODULE_PARM_DESC(rds_ib_retry_count, " Number of hw retries before reporting an error"); +/* + * we have a clumsy combination of RCU and a rwsem protecting this list + * because it is used both in the get_mr fast path and while blocking in + * the FMR flushing path. + */ +DECLARE_RWSEM(rds_ib_devices_lock); struct list_head rds_ib_devices; /* NOTE: if also grabbing ibdev lock, grab this first */ @@ -171,7 +177,10 @@ void rds_ib_add_one(struct ib_device *device) INIT_LIST_HEAD(&rds_ibdev->ipaddr_list); INIT_LIST_HEAD(&rds_ibdev->conn_list); - list_add_tail(&rds_ibdev->list, &rds_ib_devices); + + down_write(&rds_ib_devices_lock); + list_add_tail_rcu(&rds_ibdev->list, &rds_ib_devices); + up_write(&rds_ib_devices_lock); atomic_inc(&rds_ibdev->refcount); ib_set_client_data(device, &rds_ib_client, rds_ibdev); @@ -230,16 +239,20 @@ void rds_ib_remove_one(struct ib_device *device) rds_ib_dev_shutdown(rds_ibdev); + /* stop connection attempts from getting a reference to this device. */ + ib_set_client_data(device, &rds_ib_client, NULL); + + down_write(&rds_ib_devices_lock); + list_del_rcu(&rds_ibdev->list); + up_write(&rds_ib_devices_lock); + /* - * prevent future connection attempts from getting a reference to this - * device and wait for currently racing connection attempts to finish - * getting their reference + * This synchronize rcu is waiting for readers of both the ib + * client data and the devices list to finish before we drop + * both of those references. */ - ib_set_client_data(device, &rds_ib_client, NULL); synchronize_rcu(); rds_ib_dev_put(rds_ibdev); - - list_del(&rds_ibdev->list); rds_ib_dev_put(rds_ibdev); } -- cgit v1.2.3