From 9450918293b3c35f11883231a53da1aed2c78403 Mon Sep 17 00:00:00 2001 From: Nicholas Bellinger Date: Wed, 29 Jul 2015 22:27:13 -0700 Subject: [PATCH] target: Perform RCU callback barrier before backend/fabric unload This patch addresses a v4.2-rc1 regression where backend driver module unload happening immediately after TBO->free_device() does internal call_rcu(), will currently result in IRQ context rcu_process_callbacks() use-after-free paging OOPsen. It adds the missing rcu_barrier() in target_backend_unregister() to perform an explicit RCU barrier waiting for all RCU callbacks to complete before releasing target_backend_ops memory, and allowing TBO->module exit to proceed. Also, do the same for fabric drivers in target_unregister_template() to ensure se_deve_entry->rcu_head -> kfree_rcu() callbacks have completed, before allowing target_core_fabric_ops->owner module exit to proceed. Acked-by: Paul E. McKenney Cc: Christoph Hellwig Cc: Hannes Reinecke Cc: Sagi Grimberg Signed-off-by: Nicholas Bellinger --- drivers/target/target_core_configfs.c | 9 ++++++++- drivers/target/target_core_hba.c | 10 +++++++++- 2 files changed, 17 insertions(+), 2 deletions(-) diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c index c2e9fea90b4a..860e84046177 100644 --- a/drivers/target/target_core_configfs.c +++ b/drivers/target/target_core_configfs.c @@ -457,8 +457,15 @@ void target_unregister_template(const struct target_core_fabric_ops *fo) if (!strcmp(t->tf_ops->name, fo->name)) { BUG_ON(atomic_read(&t->tf_access_cnt)); list_del(&t->tf_list); + mutex_unlock(&g_tf_lock); + /* + * Wait for any outstanding fabric se_deve_entry->rcu_head + * callbacks to complete post kfree_rcu(), before allowing + * fabric driver unload of TFO->module to proceed. + */ + rcu_barrier(); kfree(t); - break; + return; } } mutex_unlock(&g_tf_lock); diff --git a/drivers/target/target_core_hba.c b/drivers/target/target_core_hba.c index 62ea4e8e70a8..be9cefc07407 100644 --- a/drivers/target/target_core_hba.c +++ b/drivers/target/target_core_hba.c @@ -84,8 +84,16 @@ void target_backend_unregister(const struct target_backend_ops *ops) list_for_each_entry(tb, &backend_list, list) { if (tb->ops == ops) { list_del(&tb->list); + mutex_unlock(&backend_mutex); + /* + * Wait for any outstanding backend driver ->rcu_head + * callbacks to complete post TBO->free_device() -> + * call_rcu(), before allowing backend driver module + * unload of target_backend_ops->owner to proceed. + */ + rcu_barrier(); kfree(tb); - break; + return; } } mutex_unlock(&backend_mutex); -- GitLab