nvme: protect against simultaneous shutdown invocations

BugLink: http://bugs.launchpad.net/bugs/1531539Signed-off-by: Keith Busch <keith.busch@intel.com>
[hch: split from a larger patch]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

(cherry picked from commit 77bf25ea)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

drivers/nvme/host/pci.c

@@ -31,6 +31,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
+#include <linux/mutex.h>
 #include <linux/pci.h>
 #include <linux/poison.h>
 #include <linux/ptrace.h>
@@ -113,6 +114,7 @@ struct nvme_dev {
 	struct work_struct reset_work;
 	struct work_struct probe_work;
 	struct work_struct scan_work;
+	struct mutex shutdown_lock;
 	bool subsystem;
 	void __iomem *cmb;
 	dma_addr_t cmb_dma_addr;
@@ -2085,6 +2087,7 @@ static void nvme_dev_shutdown(struct nvme_dev *dev)
 
 	nvme_dev_list_remove(dev);
 
+	mutex_lock(&dev->shutdown_lock);
 	if (dev->bar) {
 		nvme_freeze_queues(dev);
 		csts = readl(dev->bar + NVME_REG_CSTS);
@@ -2103,6 +2106,7 @@ static void nvme_dev_shutdown(struct nvme_dev *dev)
 
 	for (i = dev->queue_count - 1; i >= 0; i--)
 		nvme_clear_queue(dev->queues[i]);
+	mutex_unlock(&dev->shutdown_lock);
 }
 
 static int nvme_setup_prp_pools(struct nvme_dev *dev)
@@ -2345,6 +2349,7 @@ static int nvme_probe(struct pci_dev *pdev, const struct pci_device_id *id)
 	INIT_WORK(&dev->scan_work, nvme_dev_scan);
 	INIT_WORK(&dev->probe_work, nvme_probe_work);
 	INIT_WORK(&dev->reset_work, nvme_reset_work);
+	mutex_init(&dev->shutdown_lock);
 
 	result = nvme_setup_prp_pools(dev);
 	if (result)