[PATCH v3 10/11] drivers/misc/vmw_vmci: convert num guest devices counter to counter_atomic32

Shuah Khan
2020-10-09T15:56:50Z

counter_atomic* is introduced to be used when a variable is used as
a simple counter and doesn't guard object lifetimes. This clearly
differentiates atomic_t usages that guard object lifetimes.

counter_atomic* variables wrap around to INT_MIN when it overflows and
should not be used to guard resource lifetimes, device usage and open
counts that control state changes, and pm states.

atomic_t variable used to count number of vmci guest devices is used
as just as counter and it doesn't control object lifetimes or state
management. vmci_num_guest_devices is used as bool flag to determine
if a guest instance exists. There is a very little chance for this
counter to overflow.

Convert it to use counter_atomic32.

This conversion doesn't change the overflow wrap around behavior.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
drivers/misc/vmw_vmci/vmci_guest.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/vmw_vmci/vmci_guest.c b/drivers/misc/vmw_vmci/vmci_guest.c
index cc8eeb361fcd..8f6aca974b5f 100644
--- a/drivers/misc/vmw_vmci/vmci_guest.c
+++ b/drivers/misc/vmw_vmci/vmci_guest.c
@@ -20,6 +20,7 @@
#include <linux/smp.h>
#include <linux/io.h>
#include <linux/vmalloc.h>
+#include <linux/counters.h>

#include "vmci_datagram.h"
#include "vmci_doorbell.h"
@@ -68,11 +69,11 @@ struct pci_dev *vmci_pdev;
static struct vmci_guest_device *vmci_dev_g;
static DEFINE_SPINLOCK(vmci_dev_spinlock);

-static atomic_t vmci_num_guest_devices = ATOMIC_INIT(0);
+static struct counter_atomic32 vmci_num_guest_devices = COUNTER_ATOMIC_INIT(0);

bool vmci_guest_code_active(void)
{
- return atomic_read(&vmci_num_guest_devices) != 0;
+ return counter_atomic32_read(&vmci_num_guest_devices) > 0;
}

u32 vmci_get_vm_context_id(void)
@@ -624,7 +625,7 @@ static int vmci_guest_probe_device(struct pci_dev *pdev,

dev_dbg(&pdev->dev, "Registered device\n");

- atomic_inc(&vmci_num_guest_devices);
+ counter_atomic32_inc(&vmci_num_guest_devices);

/* Enable specific interrupt bits. */
cmd = VMCI_IMR_DATAGRAM;
@@ -684,7 +685,7 @@ static void vmci_guest_remove_device(struct pci_dev *pdev)

dev_dbg(&pdev->dev, "Removing device\n");

- atomic_dec(&vmci_num_guest_devices);
+ counter_atomic32_dec(&vmci_num_guest_devices);

vmci_qp_guest_endpoints_exit();

--
2.25.1