From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
This patch addresses a v4.2-rc1 regression where backend driver
struct module unload immediately after ->free_device() has done
an internal call_rcu(), results in IRQ rcu_process_callbacks()
use-after-free paging OOPsen.
It adds a explicit synchronize_rcu() in target_backend_unregister()
to wait a full RCU grace period before releasing target_backend_ops
memory, and allowing TBO->module exit to proceed.
Also, go ahead and do the same for target_unregister_template()
to ensure se_deve_entry->rcu_head -> kfree_rcu() grace period has
passed, before allowing target_core_fabric_ops->owner module exit
to proceed.
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Hannes Reinecke <hare@xxxxxxx>
Cc: Sagi Grimberg <sagig@xxxxxxxxxxxx>
Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
---
drivers/target/target_core_configfs.c | 10 +++++++++-
drivers/target/target_core_hba.c | 10 +++++++++-
2 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/drivers/target/target_core_configfs.c b/drivers/target/target_core_configfs.c
index c2e9fea..b4c3ae0 100644
--- a/drivers/target/target_core_configfs.c
+++ b/drivers/target/target_core_configfs.c
@@ -457,8 +457,16 @@ 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);
+ /*
+ * Allow any outstanding fabric se_deve_entry->rcu_head
+ * grace periods to expire post kfree_rcu(), before allowing
+ * fabric driver unload of target_core_fabric_ops->module
+ * to proceed.
+ */
+ synchronize_rcu();
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 62ea4e8..0fb830b 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);
+ /*
+ * Allow any outstanding backend driver ->rcu_head grace
+ * period to expire post ->free_device() -> call_rcu(),
+ * before allowing backend driver module unload of
+ * target_backend_ops->owner to proceed.
+ */
+ synchronize_rcu();
kfree(tb);
- break;
+ return;
}
}
mutex_unlock(&backend_mutex);
--
1.9.1
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