[PATCH] drivers:uio: Fix system crashes during driver switchover

["zhanghongtao (A)" <zhanghongtao22@huawei.com>]

From: Hongtao Zhang <zhanghongtao22@huawei.com>

Switch the driver of the SPDK program that is being read and written from the uio_pci_generic driver to the NVMe driver
(Unbind the UIO driver from the device and bind the NVMe driver to the device.) ,the system crashes and restarts.
Bug reproduction: When the SPDK is reading or writing data, run the following command: /opt/spdk/setup.sh reset
The one with a higher probability of occurrence is as follows:
PANIC: "BUG: unable to handle kernel NULL pointer dereference at 0000000000000008"
    [exception RIP: _raw_spin_lock_irqsave+30]
    RIP: ffffffff836a1cae  RSP: ffff8bca9ecc3f20  RFLAGS: 00010046
    RAX: 0000000000000000  RBX: 0000000000000246  RCX: 0000000000000017
    RDX: 0000000000000001  RSI: 0000000000000000  RDI: 0000000000000008
    RBP: 0000000000000000   R8: 000000afb34e50f9   R9: 0000000000000000
    R10: 0000000000000000  R11: 0000000000000000  R12: ffff8bca9ecc3f50
    R13: 0000000000000004  R14: 0000000000000004  R15: 0000000000000000
    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
 #7 [ffff8bca9ecc3f28] complete at ffffffff82f09bb8
reason:After the driver switchover, the upper-layer program can still access the bar space of the NVMe disk controller and knock the doorbell.
To solve this problem, a reference counting is added to prevent unbind execution before the application is closed or exited.

Signed-off-by: Hongtao Zhang <zhanghongtao22@huawei.com>
Reviewed-by: Weifeng Su <suweifeng1@huawei.com>
---
 drivers/uio/uio.c          | 13 +++++++++++++
 include/linux/uio_driver.h |  1 +
 2 files changed, 14 insertions(+)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 43afbb7c5ab9..cb8ed29a8648 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -31,6 +31,7 @@ static int uio_major;
 static struct cdev *uio_cdev;
 static DEFINE_IDR(uio_idr);
 static const struct file_operations uio_fops;
+static DECLARE_WAIT_QUEUE_HEAD(refc_wait);

 /* Protect idr accesses */
 static DEFINE_MUTEX(minor_lock);
@@ -501,6 +502,7 @@ static int uio_open(struct inode *inode, struct file *filep)
 	mutex_unlock(&idev->info_lock);
 	if (ret)
 		goto err_infoopen;
+	refcount_inc(&idev->dev_refc);

 	return 0;

@@ -536,6 +538,9 @@ static int uio_release(struct inode *inode, struct file *filep)
 		ret = idev->info->release(idev->info, inode);
 	mutex_unlock(&idev->info_lock);

+	if (refcount_dec_and_test(&idev->dev_refc))
+			wake_up(&refc_wait);
+
 	module_put(idev->owner);
 	kfree(listener);
 	put_device(&idev->dev);
@@ -937,6 +942,7 @@ int __uio_register_device(struct module *owner,

 	idev->owner = owner;
 	idev->info = info;
+	refcount_set(&idev->dev_refc, 0);
 	mutex_init(&idev->info_lock);
 	init_waitqueue_head(&idev->wait);
 	atomic_set(&idev->event, 0);
@@ -1045,6 +1051,7 @@ void uio_unregister_device(struct uio_info *info)
 {
 	struct uio_device *idev;
 	unsigned long minor;
+	unsigned int dref_count;

 	if (!info || !info->uio_dev)
 		return;
@@ -1052,6 +1059,12 @@ void uio_unregister_device(struct uio_info *info)
 	idev = info->uio_dev;
 	minor = idev->minor;

+	dref_count = refcount_read(&idev->dev_refc);
+	if (dref_count > 0) {
+		dev_err(&idev->dev, "The device is in use, please close the file descriptor or kill the occupied process\n");
+		wait_event(refc_wait, !refcount_read(&idev->dev_refc));
+	}
+
 	mutex_lock(&idev->info_lock);
 	uio_dev_del_attributes(idev);

diff --git a/include/linux/uio_driver.h b/include/linux/uio_driver.h
index 47c5962b876b..28301dcc4d31 100644
--- a/include/linux/uio_driver.h
+++ b/include/linux/uio_driver.h
@@ -77,6 +77,7 @@ struct uio_device {
 	struct mutex		info_lock;
 	struct kobject          *map_dir;
 	struct kobject          *portio_dir;
+	refcount_t				dev_refc;
 };

 /**
-- 
2.27.0