[PATCH] igb_uio: fix refcount if open returns error

[Stephen Hemminger <stephen@networkplumber.org>]

This fixes the problem of reference count leak if
igbuio_pci_enable_interrupts fails.

Also, replace mutex and integer with a kernel atomic counter.
This is standard pattern for kernel devices.

Fixes: 19685d5aa79c ("igb_uio: allow multi-process access")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
---
 kernel/linux/igb_uio/igb_uio.c | 33 +++++++++++----------------------
 1 file changed, 11 insertions(+), 22 deletions(-)

diff --git a/kernel/linux/igb_uio/igb_uio.c b/kernel/linux/igb_uio/igb_uio.c
index 3398eacd3fcc..fede66cf2735 100644
--- a/kernel/linux/igb_uio/igb_uio.c
+++ b/kernel/linux/igb_uio/igb_uio.c
@@ -26,8 +26,7 @@ struct rte_uio_pci_dev {
 	struct uio_info info;
 	struct pci_dev *pdev;
 	enum rte_intr_mode mode;
-	struct mutex lock;
-	int refcnt;
+	atomic_t refcnt;
 };
 
 static int wc_activate;
@@ -320,23 +319,19 @@ igbuio_pci_open(struct uio_info *info, struct inode *inode)
 	struct pci_dev *dev = udev->pdev;
 	int err;
 
-	mutex_lock(&udev->lock);
-	if (++udev->refcnt > 1) {
-		mutex_unlock(&udev->lock);
+	if (atomic_inc_return(&udev->refcnt) != 1)
 		return 0;
-	}
 
 	/* set bus master, which was cleared by the reset function */
 	pci_set_master(dev);
 
 	/* enable interrupts */
 	err = igbuio_pci_enable_interrupts(udev);
-	mutex_unlock(&udev->lock);
 	if (err) {
+		atomic_dec(&udev->refcnt);
 		dev_err(&dev->dev, "Enable interrupt fails\n");
-		return err;
 	}
-	return 0;
+	return err;
 }
 
 static int
@@ -345,19 +340,14 @@ igbuio_pci_release(struct uio_info *info, struct inode *inode)
 	struct rte_uio_pci_dev *udev = info->priv;
 	struct pci_dev *dev = udev->pdev;
 
-	mutex_lock(&udev->lock);
-	if (--udev->refcnt > 0) {
-		mutex_unlock(&udev->lock);
-		return 0;
-	}
-
-	/* disable interrupts */
-	igbuio_pci_disable_interrupts(udev);
+	if (atomic_dec_and_test(&udev->refcnt)) {
+		/* disable interrupts */
+		igbuio_pci_disable_interrupts(udev);
 
-	/* stop the device from further DMA */
-	pci_clear_master(dev);
+		/* stop the device from further DMA */
+		pci_clear_master(dev);
+	}
 
-	mutex_unlock(&udev->lock);
 	return 0;
 }
 
@@ -489,7 +479,6 @@ igbuio_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
 	if (!udev)
 		return -ENOMEM;
 
-	mutex_init(&udev->lock);
 	/*
 	 * enable device: ask low-level code to enable I/O and
 	 * memory
@@ -529,6 +518,7 @@ igbuio_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
 	udev->info.release = igbuio_pci_release;
 	udev->info.priv = udev;
 	udev->pdev = dev;
+	atomic_set(&udev->refcnt, 0);
 
 	err = sysfs_create_group(&dev->dev.kobj, &dev_attr_grp);
 	if (err != 0)
@@ -580,7 +570,6 @@ igbuio_pci_remove(struct pci_dev *dev)
 {
 	struct rte_uio_pci_dev *udev = pci_get_drvdata(dev);
 
-	mutex_destroy(&udev->lock);
 	sysfs_remove_group(&dev->dev.kobj, &dev_attr_grp);
 	uio_unregister_device(&udev->info);
 	igbuio_pci_release_iomem(&udev->info);
-- 
2.18.0