[PATCH 5.6 31/38] RDMA/cma: Teach lockdep about the order of rtnl and lock

Greg Kroah-Hartman
2020-04-11T12:21:45Z

From: Jason Gunthorpe <jgg@mellanox.com>

commit 32ac9e4399b12d3e54d312a0e0e30ed5cd19bd4e upstream.

This lock ordering only happens when bonding is enabled and a certain
bonding related event fires. However, since it can happen this is a global
restriction on lock ordering.

Teach lockdep about the order directly and unconditionally so bugs here
are found quickly.

See https://syzkaller.appspot.com/bug?extid=55de90ab5f44172b0c90

Link: https://lore.kernel.org/r/20200227203651.GA27185@ziepe.ca
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/infiniband/core/cma.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -4790,6 +4790,19 @@ static int __init cma_init(void)
{
int ret;

+ /*
+ * There is a rare lock ordering dependency in cma_netdev_callback()
+ * that only happens when bonding is enabled. Teach lockdep that rtnl
+ * must never be nested under lock so it can find these without having
+ * to test with bonding.
+ */
+ if (IS_ENABLED(CONFIG_LOCKDEP)) {
+ rtnl_lock();
+ mutex_lock(&lock);
+ mutex_unlock(&lock);
+ rtnl_unlock();
+ }
+
cma_wq = alloc_ordered_workqueue("rdma_cm", WQ_MEM_RECLAIM);
if (!cma_wq)
return -ENOMEM;