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

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Date:   Fri,  9 Oct 2020 09:56:05 -0600
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     arnd@...db.de, gregkh@...uxfoundation.org, keescook@...omium.org
Cc:     Shuah Khan <skhan@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 10/11] drivers/misc/vmw_vmci: convert num guest devices counter to counter_atomic32

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@...uxfoundation.org>
Signed-off-by: Shuah Khan <skhan@...uxfoundation.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