Currently the RDMA subsystem's device list and client list are protected by a single mutex. This prevents adding user-facing APIs that iterate these lists, since using them may cause a deadlock. The patch attempts to solve this problem by adding a read-write semaphore to protect the lists. Readers now don't need the mutex, and are safe just by read-locking the semaphore. The ib_register_device, ib_register_client, ib_unregister_device, and ib_unregister_client functions are modified to lock the semaphore for write during their respective list modification This patch attempts to solve a similar need [1] that was seen in the RoCE v2 patch series. [1] http://www.spinics.net/lists/linux-rdma/msg24733.html Cc: Matan Barak <matanb@xxxxxxxxxxxx> Cc: Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Haggai Eran <haggaie@xxxxxxxxxxxx> --- drivers/infiniband/core/device.c | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) diff --git a/drivers/infiniband/core/device.c b/drivers/infiniband/core/device.c index b360350a0b20..3a44723c6b9d 100644 --- a/drivers/infiniband/core/device.c +++ b/drivers/infiniband/core/device.c @@ -59,13 +59,17 @@ static LIST_HEAD(device_list); static LIST_HEAD(client_list); /* - * device_mutex protects access to both device_list and client_list. - * There's no real point to using multiple locks or something fancier - * like an rwsem: we always access both lists, and we're always - * modifying one list or the other list. In any case this is not a - * hot path so there's no point in trying to optimize. + * device_mutex and lists_rwsem protect access to both device_list and + * client_list. device_mutex protects writer access by device and client + * registration / de-registration. lists_rwsem protects reader access to + * these lists. Iterators of these lists must lock it for read, while updates + * to the lists must be done with a write lock. A special case is when the + * device_mutex is locked. In this case locking the lists for read access as + * the device_mutex implies it. */ static DEFINE_MUTEX(device_mutex); +static DECLARE_RWSEM(lists_rwsem); + static int ib_device_check_mandatory(struct ib_device *device) { @@ -311,7 +315,9 @@ int ib_register_device(struct ib_device *device, goto out; } + down_write(&lists_rwsem); list_add_tail(&device->core_list, &device_list); + up_write(&lists_rwsem); device->reg_state = IB_DEV_REGISTERED; @@ -347,7 +353,9 @@ void ib_unregister_device(struct ib_device *device) if (client->remove) client->remove(device); + down_write(&lists_rwsem); list_del(&device->core_list); + up_write(&lists_rwsem); kfree(device->gid_tbl_len); kfree(device->pkey_tbl_len); @@ -384,7 +392,10 @@ int ib_register_client(struct ib_client *client) mutex_lock(&device_mutex); + down_write(&lists_rwsem); list_add_tail(&client->list, &client_list); + up_write(&lists_rwsem); + list_for_each_entry(device, &device_list, core_list) if (client->add && !add_client_context(device, client)) client->add(device); @@ -423,7 +434,10 @@ void ib_unregister_client(struct ib_client *client) } spin_unlock_irqrestore(&device->client_data_lock, flags); } + + down_write(&lists_rwsem); list_del(&client->list); + up_write(&lists_rwsem); mutex_unlock(&device_mutex); } -- 1.7.11.2 -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
