From: Ming Lei <ming.lei@redhat.com>
Date: Thu, 9 Nov 2017 19:32:07 +0800
Subject: nvme-pci: avoid dereference of symbol from unloaded module
Patch-mainline: v4.15-rc1
Git-commit: 03e0f3a65e4da497c3b7b213c68943cbc73a2e34
References: FATE#323952, FATE#322506

The 'remove_work' may be scheduled to run after nvme_remove()
returns since we can't simply cancel it in nvme_remove() for
avoiding deadlock. Once nvme_remove() returns, this module(nvme)
can be unloaded.

On the other hand, nvme_put_ctrl() calls ctr->ops->free_ctrl
which may point to nvme_pci_free_ctrl() in unloaded module.

This patch avoids this issue by queuing 'remove_work' via 'nvme_wq',
and flush this worqueue in nvme_exit() as suggested by Sagi.

Suggested-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 drivers/nvme/host/pci.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2280,7 +2280,7 @@ static void nvme_remove_dead_ctrl(struct
 
 	nvme_get_ctrl(&dev->ctrl);
 	nvme_dev_disable(dev, false);
-	if (!schedule_work(&dev->remove_work))
+	if (!queue_work(nvme_wq, &dev->remove_work))
 		nvme_put_ctrl(&dev->ctrl);
 }
 
@@ -2702,6 +2702,7 @@ static int __init nvme_init(void)
 static void __exit nvme_exit(void)
 {
 	pci_unregister_driver(&nvme_driver);
+	flush_workqueue(nvme_wq);
 	_nvme_check_size();
 }