nvme-pci: avoid dereference of symbol from unloaded module

Ming Lei · axboe · commit 03e0f3a65e4d · 2017-11-10T19:53:25.000-07:00
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-&gt;ops-&gt;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 &lt;sagi@grimberg.me&gt;
Signed-off-by: Ming Lei &lt;ming.lei@redhat.com&gt;
Reviewed-by: Keith Busch &lt;keith.busch@intel.com&gt;
Reviewed-by: Sagi Grimberg &lt;sagi@grimberg.me&gt;
Signed-off-by: Christoph Hellwig &lt;hch@lst.de&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
@@ -2280,7 +2280,7 @@ static void nvme_remove_dead_ctrl(struct nvme_dev *dev, int status)
 
 	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);
 }
 
@@ -2703,6 +2703,7 @@ static int __init nvme_init(void)
 static void __exit nvme_exit(void)
 {
 	pci_unregister_driver(&nvme_driver);
+	flush_workqueue(nvme_wq);
 	_nvme_check_size();
 }
 

Original file line number	Diff line number	Diff line change
`@@ -2280,7 +2280,7 @@ static void nvme_remove_dead_ctrl(struct nvme_dev *dev, int status)`
`2280`	`2280`
`2281`	`2281`	`nvme_get_ctrl(&dev->ctrl);`
`2282`	`2282`	`nvme_dev_disable(dev, false);`
`2283`		`- if (!schedule_work(&dev->remove_work))`
	`2283`	`+ if (!queue_work(nvme_wq, &dev->remove_work))`
`2284`	`2284`	`nvme_put_ctrl(&dev->ctrl);`
`2285`	`2285`	`}`
`2286`	`2286`
`@@ -2703,6 +2703,7 @@ static int __init nvme_init(void)`
`2703`	`2703`	`static void __exit nvme_exit(void)`
`2704`	`2704`	`{`
`2705`	`2705`	`pci_unregister_driver(&nvme_driver);`
	`2706`	`+ flush_workqueue(nvme_wq);`
`2706`	`2707`	`_nvme_check_size();`
`2707`	`2708`	`}`
`2708`	`2709`