[RFC PATCH 00/11] Introduce Simple atomic and non-atomic counters

[RFC PATCH 00/11] Introduce Simple atomic and non-atomic counters

[Shuah Khan]

This patch series is a result of discussion at the refcount_t BOF
the Linux Plumbers Conference. In this discussion, we identifed
a need for looking closely and investigating atomic_t usages in
the kernel when it is used strictly as a counter wothout it
controlling object lifetimes and state changes.

There are a number of atomic_t usages in the kernel where atomic_t api
is used strictly for counting and not for managing object lifetime. In
some cases, atomic_t might not even be needed.
    
The purpose of these counters is twofold: 1. clearly differentiate
atomic_t counters from atomic_t usages that guard object lifetimes,
hence prone to overflow and underflow errors. It allows tools that scan
for underflow and overflow on atomic_t usages to detect overflow and
underflows to scan just the cases that are prone to errors. 2. provides
non-atomic counters for cases where atomic isn't necessary.
    
Simple atomic and non-atomic counters api provides interfaces for simple
atomic and non-atomic counters that just count, and don't guard resource
lifetimes. Counters will wrap around to 0 when it overflows and should
not be used to guard resource lifetimes, device usage and open counts
that control state changes, and pm states.
    
Using counter_atomic to guard lifetimes could lead to use-after free
when it overflows and undefined behavior when used to manage state
changes and device usage/open states.

This patch series introduces Simple atomic and non-atomic counters.
Counter atomic ops leverage atomic_t and provide a sub-set of atomic_t
ops.

In addition this patch series converts a few drivers to use the new api.
The following criteria is used for select variables for conversion:

1. Variable doesn't guard object lifetimes, manage state changes e.g:
   device usage counts, device open counts, and pm states.
2. Variable is used for stats and counters.
3. The conversion doesn't change the overflow behavior.

Please review and let me know if non-stat conversions e.g: probe_count,
deferred_trigger_count make sense.

Shuah Khan (11):
  counters: Introduce counter and counter_atomic counters
  selftests:lib:test_counters: add new test for counters
  drivers/base: convert deferred_trigger_count and probe_count to
    counter_atomic
  drivers/base/devcoredump: convert devcd_count to counter_atomic
  drivers/acpi: convert seqno counter_atomic
  drivers/acpi/apei: convert seqno counter_atomic
  drivers/android/binder: convert stats, transaction_log to
    counter_atomic
  drivers/base/test/test_async_driver_probe: convert to use
    counter_atomic
  drivers/char/ipmi: convert stats to use counter_atomic
  drivers/misc/vmw_vmci: convert num guest devices counter to
    counter_atomic
  drivers/edac: convert pci counters to counter_atomic

 Documentation/core-api/counters.rst          | 158 +++++++++
 MAINTAINERS                                  |   8 +
 drivers/acpi/acpi_extlog.c                   |   5 +-
 drivers/acpi/apei/ghes.c                     |   5 +-
 drivers/android/binder.c                     |  41 +--
 drivers/android/binder_internal.h            |   3 +-
 drivers/base/dd.c                            |  19 +-
 drivers/base/devcoredump.c                   |   5 +-
 drivers/base/test/test_async_driver_probe.c  |  23 +-
 drivers/char/ipmi/ipmi_msghandler.c          |   9 +-
 drivers/char/ipmi/ipmi_si_intf.c             |   9 +-
 drivers/edac/edac_pci.h                      |   5 +-
 drivers/edac/edac_pci_sysfs.c                |  28 +-
 drivers/misc/vmw_vmci/vmci_guest.c           |   9 +-
 include/linux/counters.h                     | 343 +++++++++++++++++++
 lib/Kconfig                                  |  10 +
 lib/Makefile                                 |   1 +
 lib/test_counters.c                          | 283 +++++++++++++++
 tools/testing/selftests/lib/Makefile         |   1 +
 tools/testing/selftests/lib/config           |   1 +
 tools/testing/selftests/lib/test_counters.sh |   5 +
 21 files changed, 897 insertions(+), 74 deletions(-)
 create mode 100644 Documentation/core-api/counters.rst
 create mode 100644 include/linux/counters.h
 create mode 100644 lib/test_counters.c
 create mode 100755 tools/testing/selftests/lib/test_counters.sh

-- 
2.25.1

[RFC PATCH 11/11] drivers/edac: convert pci counters to counter_atomic

[Shuah Khan]

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 will wrap around to 0 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 variables used for pci counters keep track of pci parity and
non-parity errors. Overflow will wrap around and reset the counts as
was the case prior to the conversion.

Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
---
 drivers/edac/edac_pci.h       |  5 +++--
 drivers/edac/edac_pci_sysfs.c | 28 ++++++++++++++--------------
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/drivers/edac/edac_pci.h b/drivers/edac/edac_pci.h
index 5175f5724cfa..2f8a21e56377 100644
--- a/drivers/edac/edac_pci.h
+++ b/drivers/edac/edac_pci.h
@@ -30,12 +30,13 @@
 #include <linux/pci.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>
+#include <linux/counters.h>
 
 #ifdef CONFIG_PCI
 
 struct edac_pci_counter {
-	atomic_t pe_count;
-	atomic_t npe_count;
+	struct counter_atomic pe_count;
+	struct counter_atomic npe_count;
 };
 
 /*
diff --git a/drivers/edac/edac_pci_sysfs.c b/drivers/edac/edac_pci_sysfs.c
index 53042af7262e..fccec2677907 100644
--- a/drivers/edac/edac_pci_sysfs.c
+++ b/drivers/edac/edac_pci_sysfs.c
@@ -23,8 +23,8 @@ static int edac_pci_log_pe = 1;		/* log PCI parity errors */
 static int edac_pci_log_npe = 1;	/* log PCI non-parity error errors */
 static int edac_pci_poll_msec = 1000;	/* one second workq period */
 
-static atomic_t pci_parity_count = ATOMIC_INIT(0);
-static atomic_t pci_nonparity_count = ATOMIC_INIT(0);
+static struct counter_atomic pci_parity_count = COUNTER_ATOMIC_INIT(0);
+static struct counter_atomic pci_nonparity_count = COUNTER_ATOMIC_INIT(0);
 
 static struct kobject *edac_pci_top_main_kobj;
 static atomic_t edac_pci_sysfs_refcount = ATOMIC_INIT(0);
@@ -58,13 +58,13 @@ int edac_pci_get_poll_msec(void)
 /**************************** EDAC PCI sysfs instance *******************/
 static ssize_t instance_pe_count_show(struct edac_pci_ctl_info *pci, char *data)
 {
-	return sprintf(data, "%u\n", atomic_read(&pci->counters.pe_count));
+	return sprintf(data, "%u\n", counter_atomic_read(&pci->counters.pe_count));
 }
 
 static ssize_t instance_npe_count_show(struct edac_pci_ctl_info *pci,
 				char *data)
 {
-	return sprintf(data, "%u\n", atomic_read(&pci->counters.npe_count));
+	return sprintf(data, "%u\n", counter_atomic_read(&pci->counters.npe_count));
 }
 
 #define to_instance(k) container_of(k, struct edac_pci_ctl_info, kobj)
@@ -553,7 +553,7 @@ static void edac_pci_dev_parity_test(struct pci_dev *dev)
 			edac_printk(KERN_CRIT, EDAC_PCI,
 				"Signaled System Error on %s\n",
 				pci_name(dev));
-			atomic_inc(&pci_nonparity_count);
+			counter_atomic_inc(&pci_nonparity_count);
 		}
 
 		if (status & (PCI_STATUS_PARITY)) {
@@ -561,7 +561,7 @@ static void edac_pci_dev_parity_test(struct pci_dev *dev)
 				"Master Data Parity Error on %s\n",
 				pci_name(dev));
 
-			atomic_inc(&pci_parity_count);
+			counter_atomic_inc(&pci_parity_count);
 		}
 
 		if (status & (PCI_STATUS_DETECTED_PARITY)) {
@@ -569,7 +569,7 @@ static void edac_pci_dev_parity_test(struct pci_dev *dev)
 				"Detected Parity Error on %s\n",
 				pci_name(dev));
 
-			atomic_inc(&pci_parity_count);
+			counter_atomic_inc(&pci_parity_count);
 		}
 	}
 
@@ -592,7 +592,7 @@ static void edac_pci_dev_parity_test(struct pci_dev *dev)
 				edac_printk(KERN_CRIT, EDAC_PCI, "Bridge "
 					"Signaled System Error on %s\n",
 					pci_name(dev));
-				atomic_inc(&pci_nonparity_count);
+				counter_atomic_inc(&pci_nonparity_count);
 			}
 
 			if (status & (PCI_STATUS_PARITY)) {
@@ -600,7 +600,7 @@ static void edac_pci_dev_parity_test(struct pci_dev *dev)
 					"Master Data Parity Error on "
 					"%s\n", pci_name(dev));
 
-				atomic_inc(&pci_parity_count);
+				counter_atomic_inc(&pci_parity_count);
 			}
 
 			if (status & (PCI_STATUS_DETECTED_PARITY)) {
@@ -608,7 +608,7 @@ static void edac_pci_dev_parity_test(struct pci_dev *dev)
 					"Detected Parity Error on %s\n",
 					pci_name(dev));
 
-				atomic_inc(&pci_parity_count);
+				counter_atomic_inc(&pci_parity_count);
 			}
 		}
 	}
@@ -646,7 +646,7 @@ void edac_pci_do_parity_check(void)
 	if (!check_pci_errors)
 		return;
 
-	before_count = atomic_read(&pci_parity_count);
+	before_count = counter_atomic_read(&pci_parity_count);
 
 	/* scan all PCI devices looking for a Parity Error on devices and
 	 * bridges.
@@ -658,7 +658,7 @@ void edac_pci_do_parity_check(void)
 	/* Only if operator has selected panic on PCI Error */
 	if (edac_pci_get_panic_on_pe()) {
 		/* If the count is different 'after' from 'before' */
-		if (before_count != atomic_read(&pci_parity_count))
+		if (before_count != counter_atomic_read(&pci_parity_count))
 			panic("EDAC: PCI Parity Error");
 	}
 }
@@ -686,7 +686,7 @@ void edac_pci_handle_pe(struct edac_pci_ctl_info *pci, const char *msg)
 {
 
 	/* global PE counter incremented by edac_pci_do_parity_check() */
-	atomic_inc(&pci->counters.pe_count);
+	counter_atomic_inc(&pci->counters.pe_count);
 
 	if (edac_pci_get_log_pe())
 		edac_pci_printk(pci, KERN_WARNING,
@@ -711,7 +711,7 @@ void edac_pci_handle_npe(struct edac_pci_ctl_info *pci, const char *msg)
 {
 
 	/* global NPE counter incremented by edac_pci_do_parity_check() */
-	atomic_inc(&pci->counters.npe_count);
+	counter_atomic_inc(&pci->counters.npe_count);
 
 	if (edac_pci_get_log_npe())
 		edac_pci_printk(pci, KERN_WARNING,
-- 
2.25.1